node_modules updated, buefy add to lib folder

2019-06-04 14:29:48 +02:00
parent 0a3f6ff240
commit 5d28bc36e1
3957 changed files with 306575 additions and 21738 deletions
@@ -0,0 +1,21 @@
+language: node_js
+sudo: false
+node_js: [11, 10, 9, 8, 7, 6, 5, 4]
+install:
+  - travis_retry npm install
+before_script:
+  - wget http://fastdl.mongodb.org/linux/mongodb-linux-x86_64-3.6.6.tgz
+  - tar -zxvf mongodb-linux-x86_64-3.6.6.tgz
+  - mkdir -p ./data/db/27017
+  - mkdir -p ./data/db/27000
+  - printf "\n--timeout 8000" >> ./test/mocha.opts
+  - ./mongodb-linux-x86_64-3.6.6/bin/mongod --fork --dbpath ./data/db/27017 --syslog --port 27017
+  - sleep 2
+matrix:
+  include:
+    - name: "👕Linter"
+      node_js: 10
+      before_script: skip
+      script: npm run lint
+notifications:
+  email: false
@@ -1,3 +1,213 @@
+5.5.8 / 2019-05-13
+==================
+ * fix(document): run pre save hooks on nested child schemas #7792
+ * fix(model): set $session() before validation middleware for bulkWrite/insertMany #7785 #7769 [Fonger](https://github.com/Fonger)
+ * fix(query): make `getPopulatedPaths()` return deeply populated paths #7757
+ * fix(query): suppress findAndModify deprecation warning when using `Model.findOneAndUpdate()` #7794
+ * fix: upgrade mongodb -> 3.2.4 #7794
+ * fix(document): handle a couple edge cases with atomics that happen when schema defines an array property named 'undefined' #7756
+ * docs(discriminator): correct function parameters #7786 [gfpacheco](https://github.com/gfpacheco)
+
+5.5.7 / 2019-05-09
+==================
+ * fix(model): set $session() before pre save middleware runs when calling save() with options #7742
+ * fix(model): set $session before pre remove hooks run when calling remove() with options #7742
+ * fix(schema): support `remove()` on nested path #2398
+ * fix(map): handle setting populated map element to doc #7745
+ * fix(query): return rawResult when inserting with options `{new:false,upsert:true,rawResult:true}` #7774 #7770 [LiaanM](https://github.com/LiaanM)
+ * fix(schematype): remove internal `validators` option because it conflicts with Backbone #7720
+
+5.5.6 / 2019-05-06
+==================
+ * fix(document): stop converting arrays to objects when setting non-schema path to array with strict: false #7733
+ * fix(array): make two Mongoose arrays `assert.deepEqual()` each other if they have the same values #7700
+ * fix(populate): support populating a path in a document array embedded in an array #7647
+ * fix(populate): set populate virtual count to 0 if local field is empty #7731
+ * fix(update): avoid throwing cast error if casting array filter that isn't in schema with strictQuery = false #7728
+ * docs: fix typo in `distinct()` description #7767 [phil-r](https://github.com/phil-r)
+
+5.5.5 / 2019-04-30
+==================
+ * fix(document): ensure nested properties within single nested subdocs get set correctly when overwriting single nested subdoc #7748
+ * fix(document): skip non-object `validators` in schema types #7720
+ * fix: bump mongodb driver -> 3.2.3 #7752
+ * fix(map): disallow setting map key with special properties #7750 [Fonger](https://github.com/Fonger)
+
+5.5.4 / 2019-04-25
+==================
+ * fix(document): avoid calling custom getters when saving #7719
+ * fix(timestamps): handle child schema timestamps correctly when reusing child schemas #7712
+ * fix(query): pass correct callback for _legacyFindAndModify #7736 [Fonger](https://github.com/Fonger)
+ * fix(model+query): allow setting `replacement` parameter for `findOneAndReplace()` #7654
+ * fix(map): make `delete()` unset the key in the database #7746 [Fonger](https://github.com/Fonger)
+ * fix(array): use symbol for `_schema` property to avoid confusing deep equality checks #7700
+ * fix(document): prevent `depopulate()` from removing fields with empty array #7741 #7740 [Fonger](https://github.com/Fonger)
+ * fix: make `MongooseArray#includes` support ObjectIds #7732 #6354 [hansemannn](https://github.com/hansemannn)
+ * fix(document): report correct validation error index when pushing onto doc array #7744 [Fonger](https://github.com/Fonger)
+
+5.5.3 / 2019-04-22
+==================
+ * fix: add findAndModify deprecation warning that references the useFindAndModify option #7644
+ * fix(document): handle pushing a doc onto a discriminator that contains a doc array #7704
+ * fix(update): run setters on array elements when doing $set #7679
+ * fix: correct usage of arguments while buffering commands #7718 [rzymek](https://github.com/rzymek)
+ * fix(document): avoid error clearing modified subpaths if doc not defined #7715 [bitflower](https://github.com/bitflower)
+ * refactor(array): move `_parent` property behind a symbol #7726 #7700
+ * docs(model): list out all operations and options for `bulkWrite()` #7055
+ * docs(aggregate): use `eachAsync()` instead of nonexistent `each()` #7699
+ * docs(validation): add CastError validation example #7514
+ * docs(query+model): list out all options and callback details for Model.updateX() and Query#updateX() #7646
+
+5.5.2 / 2019-04-16
+==================
+ * fix(document): support setting nested path to non-POJO object #7639
+ * perf(connection): remove leaked event handler in `Model.init()` so `deleteModel()` frees all memory #7682
+ * fix(timestamps): handle custom statics that conflict with built-in functions (like mongoose-delete plugin) #7698
+ * fix(populate): make `Document#populated()` work for populated subdocs #7685
+ * fix(document): support `.set()` on document array underneath embedded discriminator path #7656
+
+5.5.1 / 2019-04-11
+==================
+ * fix(document): correctly overwrite all properties when setting a single nested subdoc #7660 #7681
+ * fix(array): allow customization of array required validator #7696 [freewil](https://github.com/freewil)
+ * fix(discriminator): handle embedded discriminators when casting array defaults #7687
+ * fix(collection): ensure collection functions return a promise even if disconnected #7676
+ * fix(schematype): avoid indexing properties with `{ unique: false, index: false }` #7620
+ * fix(aggregate): make `Aggregate#model()` with no arguments return the aggregation's model #7608
+
+5.5.0 / 2019-04-08
+==================
+ * feat(model): support applying hooks to custom static functions #5982
+ * feat(populate): support specifying a function as `match` #7397
+ * perf(buffer): avoid calling `defineProperties()` in Buffer constructor #7331
+ * feat(connection): add `plugin()` for connection-scoped plugins #7378
+ * feat(model): add Model#deleteOne() and corresponding hooks #7538
+ * feat(query): support hooks for `Query#distinct()` #5938
+ * feat(model): print warning when calling create() incorrectly with a session #7535
+ * feat(document): add Document#isEmpty() and corresponding helpers for nested paths #5369
+ * feat(document): add `getters` option to Document#get() #7233
+ * feat(query): add Query#projection() to get or overwrite the current projection #7384
+ * fix(document): set full validator path on validatorProperties if `propsParameter` set on validator #7447
+ * feat(document): add Document#directModifiedPaths() #7373
+ * feat(document): add $locals property #7691
+ * feat(document): add validateUpdatedOnly option that only validates modified paths in `save()` #7492 [captaincaius](https://github.com/captaincaius)
+ * chore: upgrade MongoDB driver to v3.2.0 #7641
+ * fix(schematype): deprecate `isAsync` option for custom validators #6700
+ * chore(mongoose): deprecate global.MONGOOSE_DRIVER_PATH so we can be webpack-warning-free in 6.0 #7501
+
+5.4.23 / 2019-04-08
+===================
+ * fix(document): report cast error when string path in schema is an array in MongoDB #7619
+ * fix(query): set deletedCount on result of remove() #7629
+ * docs(subdocs): add note about parent() and ownerDocument() to subdocument docs #7576
+
+5.4.22 / 2019-04-04
+===================
+ * fix(aggregate): allow modifying options in pre('aggregate') hook #7606
+ * fix(map): correctly init maps of maps when loading from MongoDB #7630
+ * docs(model+query): add `omitUndefined` option to docs for updateX() and findOneAndX() #3486
+ * docs: removed duplicate Query.prototype.merge() reference from doc #7684 [shihabmridha](https://github.com/shihabmridha)
+ * docs(schema): fix shardKey type to object instead of bool #7668 [kyletsang](https://github.com/kyletsang)
+ * docs(api): fix `Model.prototypedelete` link #7665 [pixcai](https://github.com/pixcai)
+
+5.4.21 / 2019-04-02
+===================
+ * fix(updateValidators): run update validators correctly on Decimal128 paths #7561
+ * fix(update): cast array filters in nested doc arrays correctly #7603
+ * fix(document): allow .get() + .set() with aliased paths #7592
+ * fix(document): ensure custom getters on single nested subdocs don't get persisted if toObject.getters = true #7601
+ * fix(document): support setting subdoc path to subdoc copied using object rest `{...doc}` #7645
+ * docs(schema): correct out-of-date list of reserved words #7593
+ * docs(model+query): add link to update results docs and examples of using results of updateOne(), etc. #7582
+ * docs: use atomic as opposed to $atomic consistently #7649 [720degreeLotus](https://github.com/720degreeLotus)
+
+5.4.20 / 2019-03-25
+===================
+ * docs(tutorials): add tutorial about `lean()` #7640
+ * fix(discriminator): fix wrong modelName being used as value to partialFilterExpression index #7635 #7634 [egorovli](https://github.com/egorovli)
+ * fix(document): allow setters to modify `this` when overwriting single nested subdoc #7585
+ * fix(populate): handle count option correctly with multiple docs #7573
+ * fix(date): support declaring min/max validators as functions #7600 [ChienDevIT](https://github.com/ChienDevIT)
+ * fix(discriminator): avoid projecting in embedded discriminator if only auto-selected path is discriminator key #7574
+ * fix(discriminator): use discriminator model when using `new BaseModel()` with discriminator key #7586
+ * fix(timestamps): avoid throwing if doc array has timestamps and array is undefined #7625 [serg33v](https://github.com/serg33v)
+ * docs(document): explain DocumentNotFoundError in save() docs #7580
+ * docs(query): fix .all() param type and add example #7612 [720degreeLotus](https://github.com/720degreeLotus)
+ * docs: add useNewUrlParser to mongoose.connect for some pages #7615 [YC](https://github.com/YC)
+
+5.4.19 / 2019-03-11
+===================
+ * fix(mongoose): ensure virtuals set on subdocs in global plugins get applied #7592
+ * docs(tutorials): add "Working With Dates" tutorial #7597
+ * docs(guide): clarify that versioning only affects array fields #7555
+ * docs(model): list out all bulkWrite() options #7550
+
+5.4.18 / 2019-03-08
+===================
+ * fix(document): handle nested virtuals in populated docs when parent path is projected out #7491
+ * fix(model): make subclassed models handle discriminators correctly #7547
+ * fix(model): remove $versionError from save options for better debug output #7570
+
+5.4.17 / 2019-03-03
+===================
+ * fix(update): handle all positional operator when casting array filters #7540
+ * fix(populate): handle populating nested path where top-level path is a primitive in the db #7545
+ * fix(update): run update validators on array filters #7536
+ * fix(document): clean modified subpaths when sorting an array #7556
+ * fix(model): cast $setOnInsert correctly with nested docs #7534
+ * docs: remove extra curly brace from example #7569 [kolya182](https://github.com/kolya182)
+
+5.4.16 / 2019-02-26
+===================
+ * fix(schema): handle nested objects with `_id: false` #7524
+ * fix(schema): don't throw error if declaring a virtual that starts with a map path name #7464
+ * fix(browser): add stubbed `model()` function so code that uses model doesn't throw #7541 [caub](https://github.com/caub)
+ * fix(schema): merge virtuals correctly #7563 [yoursdearboy](https://github.com/yoursdearboy)
+ * docs(connections): add reconnectFailed to connection docs #7477
+ * docs(index): fix typo #7553 [DenrizSusam](https://github.com/DenrizSusam)
+ * refactor(schema): iterate over paths instead of depending on childSchemas #7554
+
+5.4.15 / 2019-02-22
+===================
+ * fix(update): don't call schematype validators on array if using $pull with runValidators #6971
+ * fix(schema): clone all schema types when cloning an array #7537
+ * docs(connections): improve connectTimeoutMS docs and socketTimeoutMS docs to link to Node.js net.setTimeout() #5169
+ * docs: fix setters example in migration guide #7546 [freewil](https://github.com/freewil)
+
+5.4.14 / 2019-02-19
+===================
+ * fix(populate): make `getters` option handle nested paths #7521
+ * fix(documentarray): report validation errors that occur in an array subdoc created using `create()` and then `set()` #7504
+ * docs(schema): add examples for schema functions that didn't have any #7525
+ * docs: add MongooseError to API docs and add list of error names
+ * docs(CONTRIBUTING): fix link #7530 [sarpik](https://github.com/sarpik)
+
+5.4.13 / 2019-02-15
+===================
+ * fix(query): throw handy error when using updateOne() with overwrite: true and no dollar keys #7475
+ * fix(schema): support inheriting existing schema types using Node.js `util.inherits` like mongoose-float #7486
+ * docs(connections): add list of connection events #7477
+
+5.4.12 / 2019-02-13
+===================
+ * fix(connection): dont emit reconnected due to socketTimeoutMS #7452
+ * fix(schema): revert check for `false` schema paths #7516 #7512
+ * fix(model): don't delete unaliased keys in translateAliases #7510 [chrischen](https://github.com/chrischen)
+ * fix(document): run single nested schematype validator if nested path has a default and subpath is modified #7493
+ * fix(query): copy mongoose options when using `Query#merge()` #1790
+ * fix(timestamps): don't call createdAt getters when setting updatedAt on new doc #7496
+ * docs: improve description of ValidationError #7515 [JulioJu](https://github.com/JulioJu)
+ * docs: add an asterisk before comment, otherwise the comment line is not generated #7513 [JulioJu](https://github.com/JulioJu)
+
+5.4.11 / 2019-02-09
+===================
+ * fix(schema): handle `_id: false` in schema paths as a shortcut for setting the `_id` option to `false` #7480
+ * fix(update): handle $addToSet and $push with ObjectIds and castNonArrays=false #7479
+ * docs(model): document `session` option to `save()` #7484
+ * chore: fix gitignore syntax #7498 [JulioJu](https://github.com/JulioJu)
+ * docs: document that Document#validateSync returns ValidationError #7499
+ * refactor: use consolidated `isPOJO()` function instead of constructor checks #7500
+
 5.4.10 / 2019-02-05
 ===================
 * docs: add search bar and /search page #6706
@@ -66,7 +66,7 @@ Both `connect` and `createConnection` take a `mongodb://` URI, or the parameters
 ```js
 const mongoose = require('mongoose');

-mongoose.connect('mongodb://localhost/my_database');
+mongoose.connect('mongodb://localhost/my_database', {useNewUrlParser: true});
 ```

 Once connected, the `open` event is fired on the `Connection` instance. If you're using `mongoose.connect`, the `Connection` is `mongoose.connection`. Otherwise, `mongoose.createConnection` return value is a `Connection`.
@@ -0,0 +1,8 @@
+/**
+ * Export lib/mongoose
+ *
+ */
+
+'use strict';
+
+module.exports = require('./lib/browser');
@@ -0,0 +1,9 @@
+
+/**
+ * Export lib/mongoose
+ *
+ */
+
+'use strict';
+
+module.exports = require('./lib/');
@@ -0,0 +1,144 @@
+/* eslint-env browser */
+
+'use strict';
+
+require('./driver').set(require('./drivers/browser'));
+
+const DocumentProvider = require('./document_provider.js');
+const PromiseProvider = require('./promise_provider');
+
+DocumentProvider.setBrowser(true);
+
+/**
+ * The Mongoose [Promise](#promise_Promise) constructor.
+ *
+ * @method Promise
+ * @api public
+ */
+
+Object.defineProperty(exports, 'Promise', {
+  get: function() {
+    return PromiseProvider.get();
+  },
+  set: function(lib) {
+    PromiseProvider.set(lib);
+  }
+});
+
+/**
+ * Storage layer for mongoose promises
+ *
+ * @method PromiseProvider
+ * @api public
+ */
+
+exports.PromiseProvider = PromiseProvider;
+
+/**
+ * The [MongooseError](#error_MongooseError) constructor.
+ *
+ * @method Error
+ * @api public
+ */
+
+exports.Error = require('./error');
+
+/**
+ * The Mongoose [Schema](#schema_Schema) constructor
+ *
+ * ####Example:
+ *
+ *     var mongoose = require('mongoose');
+ *     var Schema = mongoose.Schema;
+ *     var CatSchema = new Schema(..);
+ *
+ * @method Schema
+ * @api public
+ */
+
+exports.Schema = require('./schema');
+
+/**
+ * The various Mongoose Types.
+ *
+ * ####Example:
+ *
+ *     var mongoose = require('mongoose');
+ *     var array = mongoose.Types.Array;
+ *
+ * ####Types:
+ *
+ * - [ObjectId](#types-objectid-js)
+ * - [Buffer](#types-buffer-js)
+ * - [SubDocument](#types-embedded-js)
+ * - [Array](#types-array-js)
+ * - [DocumentArray](#types-documentarray-js)
+ *
+ * Using this exposed access to the `ObjectId` type, we can construct ids on demand.
+ *
+ *     var ObjectId = mongoose.Types.ObjectId;
+ *     var id1 = new ObjectId;
+ *
+ * @property Types
+ * @api public
+ */
+exports.Types = require('./types');
+
+/**
+ * The Mongoose [VirtualType](#virtualtype_VirtualType) constructor
+ *
+ * @method VirtualType
+ * @api public
+ */
+exports.VirtualType = require('./virtualtype');
+
+/**
+ * The various Mongoose SchemaTypes.
+ *
+ * ####Note:
+ *
+ * _Alias of mongoose.Schema.Types for backwards compatibility._
+ *
+ * @property SchemaTypes
+ * @see Schema.SchemaTypes #schema_Schema.Types
+ * @api public
+ */
+
+exports.SchemaType = require('./schematype.js');
+
+/**
+ * Internal utils
+ *
+ * @property utils
+ * @api private
+ */
+
+exports.utils = require('./utils.js');
+
+/**
+ * The Mongoose browser [Document](#document-js) constructor.
+ *
+ * @method Document
+ * @api public
+ */
+exports.Document = DocumentProvider();
+
+/**
+ * function stub for model
+ *
+ * @method model
+ * @api public
+ * @return null
+ */
+exports.model = function() {
+  return null;
+};
+
+/*!
+ * Module exports.
+ */
+
+if (typeof window !== 'undefined') {
+  window.mongoose = module.exports;
+  window.Buffer = Buffer;
+}
@@ -0,0 +1,102 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const NodeJSDocument = require('./document');
+const EventEmitter = require('events').EventEmitter;
+const MongooseError = require('./error');
+const Schema = require('./schema');
+const ObjectId = require('./types/objectid');
+const ValidationError = MongooseError.ValidationError;
+const applyHooks = require('./helpers/model/applyHooks');
+const utils = require('./utils');
+
+/**
+ * Document constructor.
+ *
+ * @param {Object} obj the values to set
+ * @param {Object} [fields] optional object containing the fields which were selected in the query returning this document and any populated paths data
+ * @param {Boolean} [skipId] bool, should we auto create an ObjectId _id
+ * @inherits NodeJS EventEmitter http://nodejs.org/api/events.html#events_class_events_eventemitter
+ * @event `init`: Emitted on a document after it has was retrieved from the db and fully hydrated by Mongoose.
+ * @event `save`: Emitted when the document is successfully saved
+ * @api private
+ */
+
+function Document(obj, schema, fields, skipId, skipInit) {
+  if (!(this instanceof Document)) {
+    return new Document(obj, schema, fields, skipId, skipInit);
+  }
+
+  if (utils.isObject(schema) && !schema.instanceOfSchema) {
+    schema = new Schema(schema);
+  }
+
+  // When creating EmbeddedDocument, it already has the schema and he doesn't need the _id
+  schema = this.schema || schema;
+
+  // Generate ObjectId if it is missing, but it requires a scheme
+  if (!this.schema && schema.options._id) {
+    obj = obj || {};
+
+    if (obj._id === undefined) {
+      obj._id = new ObjectId();
+    }
+  }
+
+  if (!schema) {
+    throw new MongooseError.MissingSchemaError();
+  }
+
+  this.$__setSchema(schema);
+
+  NodeJSDocument.call(this, obj, fields, skipId, skipInit);
+
+  applyHooks(this, schema, { decorateDoc: true });
+
+  // apply methods
+  for (const m in schema.methods) {
+    this[m] = schema.methods[m];
+  }
+  // apply statics
+  for (const s in schema.statics) {
+    this[s] = schema.statics[s];
+  }
+}
+
+/*!
+ * Inherit from the NodeJS document
+ */
+
+Document.prototype = Object.create(NodeJSDocument.prototype);
+Document.prototype.constructor = Document;
+
+/*!
+ * ignore
+ */
+
+Document.events = new EventEmitter();
+
+/*!
+ * Browser doc exposes the event emitter API
+ */
+
+Document.$emitter = new EventEmitter();
+
+utils.each(
+  ['on', 'once', 'emit', 'listeners', 'removeListener', 'setMaxListeners',
+    'removeAllListeners', 'addListener'],
+  function(emitterFn) {
+    Document[emitterFn] = function() {
+      return Document.$emitter[emitterFn].apply(Document.$emitter, arguments);
+    };
+  });
+
+/*!
+ * Module exports.
+ */
+
+Document.ValidationError = ValidationError;
+module.exports = exports = Document;
@@ -0,0 +1,340 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const StrictModeError = require('./error/strict');
+const Types = require('./schema/index');
+const castTextSearch = require('./schema/operators/text');
+const get = require('./helpers/get');
+const util = require('util');
+const utils = require('./utils');
+
+const ALLOWED_GEOWITHIN_GEOJSON_TYPES = ['Polygon', 'MultiPolygon'];
+
+/**
+ * Handles internal casting for query filters.
+ *
+ * @param {Schema} schema
+ * @param {Object} obj Object to cast
+ * @param {Object} options the query options
+ * @param {Query} context passed to setters
+ * @api private
+ */
+module.exports = function cast(schema, obj, options, context) {
+  if (Array.isArray(obj)) {
+    throw new Error('Query filter must be an object, got an array ', util.inspect(obj));
+  }
+
+  const paths = Object.keys(obj);
+  let i = paths.length;
+  let _keys;
+  let any$conditionals;
+  let schematype;
+  let nested;
+  let path;
+  let type;
+  let val;
+
+  options = options || {};
+
+  while (i--) {
+    path = paths[i];
+    val = obj[path];
+
+    if (path === '$or' || path === '$nor' || path === '$and') {
+      let k = val.length;
+
+      while (k--) {
+        val[k] = cast(schema, val[k], options, context);
+      }
+    } else if (path === '$where') {
+      type = typeof val;
+
+      if (type !== 'string' && type !== 'function') {
+        throw new Error('Must have a string or function for $where');
+      }
+
+      if (type === 'function') {
+        obj[path] = val.toString();
+      }
+
+      continue;
+    } else if (path === '$elemMatch') {
+      val = cast(schema, val, options, context);
+    } else if (path === '$text') {
+      val = castTextSearch(val, path);
+    } else {
+      if (!schema) {
+        // no casting for Mixed types
+        continue;
+      }
+
+      schematype = schema.path(path);
+
+      // Check for embedded discriminator paths
+      if (!schematype) {
+        const split = path.split('.');
+        let j = split.length;
+        while (j--) {
+          const pathFirstHalf = split.slice(0, j).join('.');
+          const pathLastHalf = split.slice(j).join('.');
+          const _schematype = schema.path(pathFirstHalf);
+          const discriminatorKey = get(_schematype, 'schema.options.discriminatorKey');
+
+          // gh-6027: if we haven't found the schematype but this path is
+          // underneath an embedded discriminator and the embedded discriminator
+          // key is in the query, use the embedded discriminator schema
+          if (_schematype != null &&
+              get(_schematype, 'schema.discriminators') != null &&
+              discriminatorKey != null &&
+              pathLastHalf !== discriminatorKey) {
+            const discriminatorVal = get(obj, pathFirstHalf + '.' + discriminatorKey);
+            if (discriminatorVal != null) {
+              schematype = _schematype.schema.discriminators[discriminatorVal].
+                path(pathLastHalf);
+            }
+          }
+        }
+      }
+
+      if (!schematype) {
+        // Handle potential embedded array queries
+        const split = path.split('.');
+        let j = split.length;
+        let pathFirstHalf;
+        let pathLastHalf;
+        let remainingConds;
+
+        // Find the part of the var path that is a path of the Schema
+        while (j--) {
+          pathFirstHalf = split.slice(0, j).join('.');
+          schematype = schema.path(pathFirstHalf);
+          if (schematype) {
+            break;
+          }
+        }
+
+        // If a substring of the input path resolves to an actual real path...
+        if (schematype) {
+          // Apply the casting; similar code for $elemMatch in schema/array.js
+          if (schematype.caster && schematype.caster.schema) {
+            remainingConds = {};
+            pathLastHalf = split.slice(j).join('.');
+            remainingConds[pathLastHalf] = val;
+            obj[path] = cast(schematype.caster.schema, remainingConds, options, context)[pathLastHalf];
+          } else {
+            obj[path] = val;
+          }
+          continue;
+        }
+
+        if (utils.isObject(val)) {
+          // handle geo schemas that use object notation
+          // { loc: { long: Number, lat: Number }
+
+          let geo = '';
+          if (val.$near) {
+            geo = '$near';
+          } else if (val.$nearSphere) {
+            geo = '$nearSphere';
+          } else if (val.$within) {
+            geo = '$within';
+          } else if (val.$geoIntersects) {
+            geo = '$geoIntersects';
+          } else if (val.$geoWithin) {
+            geo = '$geoWithin';
+          }
+
+          if (geo) {
+            const numbertype = new Types.Number('__QueryCasting__');
+            let value = val[geo];
+
+            if (val.$maxDistance != null) {
+              val.$maxDistance = numbertype.castForQueryWrapper({
+                val: val.$maxDistance,
+                context: context
+              });
+            }
+            if (val.$minDistance != null) {
+              val.$minDistance = numbertype.castForQueryWrapper({
+                val: val.$minDistance,
+                context: context
+              });
+            }
+
+            if (geo === '$within') {
+              const withinType = value.$center
+                  || value.$centerSphere
+                  || value.$box
+                  || value.$polygon;
+
+              if (!withinType) {
+                throw new Error('Bad $within parameter: ' + JSON.stringify(val));
+              }
+
+              value = withinType;
+            } else if (geo === '$near' &&
+                typeof value.type === 'string' && Array.isArray(value.coordinates)) {
+              // geojson; cast the coordinates
+              value = value.coordinates;
+            } else if ((geo === '$near' || geo === '$nearSphere' || geo === '$geoIntersects') &&
+                value.$geometry && typeof value.$geometry.type === 'string' &&
+                Array.isArray(value.$geometry.coordinates)) {
+              if (value.$maxDistance != null) {
+                value.$maxDistance = numbertype.castForQueryWrapper({
+                  val: value.$maxDistance,
+                  context: context
+                });
+              }
+              if (value.$minDistance != null) {
+                value.$minDistance = numbertype.castForQueryWrapper({
+                  val: value.$minDistance,
+                  context: context
+                });
+              }
+              if (utils.isMongooseObject(value.$geometry)) {
+                value.$geometry = value.$geometry.toObject({
+                  transform: false,
+                  virtuals: false
+                });
+              }
+              value = value.$geometry.coordinates;
+            } else if (geo === '$geoWithin') {
+              if (value.$geometry) {
+                if (utils.isMongooseObject(value.$geometry)) {
+                  value.$geometry = value.$geometry.toObject({ virtuals: false });
+                }
+                const geoWithinType = value.$geometry.type;
+                if (ALLOWED_GEOWITHIN_GEOJSON_TYPES.indexOf(geoWithinType) === -1) {
+                  throw new Error('Invalid geoJSON type for $geoWithin "' +
+                    geoWithinType + '", must be "Polygon" or "MultiPolygon"');
+                }
+                value = value.$geometry.coordinates;
+              } else {
+                value = value.$box || value.$polygon || value.$center ||
+                  value.$centerSphere;
+                if (utils.isMongooseObject(value)) {
+                  value = value.toObject({ virtuals: false });
+                }
+              }
+            }
+
+            _cast(value, numbertype, context);
+            continue;
+          }
+        }
+
+        if (schema.nested[path]) {
+          continue;
+        }
+        if (options.upsert && options.strict) {
+          if (options.strict === 'throw') {
+            throw new StrictModeError(path);
+          }
+          throw new StrictModeError(path, 'Path "' + path + '" is not in ' +
+            'schema, strict mode is `true`, and upsert is `true`.');
+        } else if (options.strictQuery === 'throw') {
+          throw new StrictModeError(path, 'Path "' + path + '" is not in ' +
+            'schema and strictQuery is true.');
+        } else if (options.strictQuery) {
+          delete obj[path];
+        }
+      } else if (val == null) {
+        continue;
+      } else if (val.constructor.name === 'Object') {
+        any$conditionals = Object.keys(val).some(function(k) {
+          return k.charAt(0) === '$' && k !== '$id' && k !== '$ref';
+        });
+
+        if (!any$conditionals) {
+          obj[path] = schematype.castForQueryWrapper({
+            val: val,
+            context: context
+          });
+        } else {
+          const ks = Object.keys(val);
+          let $cond;
+
+          let k = ks.length;
+
+          while (k--) {
+            $cond = ks[k];
+            nested = val[$cond];
+
+            if ($cond === '$not') {
+              if (nested && schematype && !schematype.caster) {
+                _keys = Object.keys(nested);
+                if (_keys.length && _keys[0].charAt(0) === '$') {
+                  for (const key in nested) {
+                    nested[key] = schematype.castForQueryWrapper({
+                      $conditional: key,
+                      val: nested[key],
+                      context: context
+                    });
+                  }
+                } else {
+                  val[$cond] = schematype.castForQueryWrapper({
+                    $conditional: $cond,
+                    val: nested,
+                    context: context
+                  });
+                }
+                continue;
+              }
+              cast(schematype.caster ? schematype.caster.schema : schema, nested, options, context);
+            } else {
+              val[$cond] = schematype.castForQueryWrapper({
+                $conditional: $cond,
+                val: nested,
+                context: context
+              });
+            }
+          }
+        }
+      } else if (Array.isArray(val) && ['Buffer', 'Array'].indexOf(schematype.instance) === -1) {
+        const casted = [];
+        for (let valIndex = 0; valIndex < val.length; valIndex++) {
+          casted.push(schematype.castForQueryWrapper({
+            val: val[valIndex],
+            context: context
+          }));
+        }
+
+        obj[path] = { $in: casted };
+      } else {
+        obj[path] = schematype.castForQueryWrapper({
+          val: val,
+          context: context
+        });
+      }
+    }
+  }
+
+  return obj;
+};
+
+function _cast(val, numbertype, context) {
+  if (Array.isArray(val)) {
+    val.forEach(function(item, i) {
+      if (Array.isArray(item) || utils.isObject(item)) {
+        return _cast(item, numbertype, context);
+      }
+      val[i] = numbertype.castForQueryWrapper({ val: item, context: context });
+    });
+  } else {
+    const nearKeys = Object.keys(val);
+    let nearLen = nearKeys.length;
+    while (nearLen--) {
+      const nkey = nearKeys[nearLen];
+      const item = val[nkey];
+      if (Array.isArray(item) || utils.isObject(item)) {
+        _cast(item, numbertype, context);
+        val[nkey] = item;
+      } else {
+        val[nkey] = numbertype.castForQuery({ val: item, context: context });
+      }
+    }
+  }
+}
@@ -0,0 +1,31 @@
+'use strict';
+
+const CastError = require('../error/cast');
+
+/*!
+ * Given a value, cast it to a boolean, or throw a `CastError` if the value
+ * cannot be casted. `null` and `undefined` are considered valid.
+ *
+ * @param {Any} value
+ * @param {String} [path] optional the path to set on the CastError
+ * @return {Boolean|null|undefined}
+ * @throws {CastError} if `value` is not one of the allowed values
+ * @api private
+ */
+
+module.exports = function castBoolean(value, path) {
+  if (value == null) {
+    return value;
+  }
+
+  if (module.exports.convertToTrue.has(value)) {
+    return true;
+  }
+  if (module.exports.convertToFalse.has(value)) {
+    return false;
+  }
+  throw new CastError('boolean', value, path);
+};
+
+module.exports.convertToTrue = new Set([true, 'true', 1, '1', 'yes']);
+module.exports.convertToFalse = new Set([false, 'false', 0, '0', 'no']);
@@ -0,0 +1,41 @@
+'use strict';
+
+const assert = require('assert');
+
+module.exports = function castDate(value) {
+  // Support empty string because of empty form values. Originally introduced
+  // in https://github.com/Automattic/mongoose/commit/efc72a1898fc3c33a319d915b8c5463a22938dfe
+  if (value == null || value === '') {
+    return null;
+  }
+
+  if (value instanceof Date) {
+    assert.ok(!isNaN(value.valueOf()));
+
+    return value;
+  }
+
+  let date;
+
+  assert.ok(typeof value !== 'boolean');
+
+  if (value instanceof Number || typeof value === 'number') {
+    date = new Date(value);
+  } else if (typeof value === 'string' && !isNaN(Number(value)) && (Number(value) >= 275761 || Number(value) < -271820)) {
+    // string representation of milliseconds take this path
+    date = new Date(Number(value));
+  } else if (typeof value.valueOf === 'function') {
+    // support for moment.js. This is also the path strings will take because
+    // strings have a `valueOf()`
+    date = new Date(value.valueOf());
+  } else {
+    // fallback
+    date = new Date(value);
+  }
+
+  if (!isNaN(date.valueOf())) {
+    return date;
+  }
+
+  assert.ok(false);
+};
@@ -0,0 +1,36 @@
+'use strict';
+
+const Decimal128Type = require('../types/decimal128');
+const assert = require('assert');
+
+module.exports = function castDecimal128(value) {
+  if (value == null) {
+    return value;
+  }
+
+  if (typeof value === 'object' && typeof value.$numberDecimal === 'string') {
+    return Decimal128Type.fromString(value.$numberDecimal);
+  }
+
+  if (value instanceof Decimal128Type) {
+    return value;
+  }
+
+  if (typeof value === 'string') {
+    return Decimal128Type.fromString(value);
+  }
+
+  if (Buffer.isBuffer(value)) {
+    return new Decimal128Type(value);
+  }
+
+  if (typeof value === 'number') {
+    return Decimal128Type.fromString(String(value));
+  }
+
+  if (typeof value.valueOf === 'function' && typeof value.valueOf() === 'string') {
+    return Decimal128Type.fromString(value.valueOf());
+  }
+
+  assert.ok(false);
+};
@@ -0,0 +1,45 @@
+'use strict';
+
+const assert = require('assert');
+
+/*!
+ * Given a value, cast it to a number, or throw a `CastError` if the value
+ * cannot be casted. `null` and `undefined` are considered valid.
+ *
+ * @param {Any} value
+ * @param {String} [path] optional the path to set on the CastError
+ * @return {Boolean|null|undefined}
+ * @throws {Error} if `value` is not one of the allowed values
+ * @api private
+ */
+
+module.exports = function castNumber(val) {
+  assert.ok(!isNaN(val));
+
+  if (val == null) {
+    return val;
+  }
+  if (val === '') {
+    return null;
+  }
+
+  if (typeof val === 'string' || typeof val === 'boolean') {
+    val = Number(val);
+  }
+
+  assert.ok(!isNaN(val));
+  if (val instanceof Number) {
+    return val;
+  }
+  if (typeof val === 'number') {
+    return val;
+  }
+  if (!Array.isArray(val) && typeof val.valueOf === 'function') {
+    return Number(val.valueOf());
+  }
+  if (val.toString && !Array.isArray(val) && val.toString() == Number(val)) {
+    return new Number(val);
+  }
+
+  assert.ok(false);
+};
@@ -0,0 +1,29 @@
+'use strict';
+
+const ObjectId = require('../driver').get().ObjectId;
+const assert = require('assert');
+
+module.exports = function castObjectId(value) {
+  if (value == null) {
+    return value;
+  }
+
+  if (value instanceof ObjectId) {
+    return value;
+  }
+
+  if (value._id) {
+    if (value._id instanceof ObjectId) {
+      return value._id;
+    }
+    if (value._id.toString instanceof Function) {
+      return new ObjectId(value._id.toString());
+    }
+  }
+
+  if (value.toString instanceof Function) {
+    return new ObjectId(value.toString());
+  }
+
+  assert.ok(false);
+};
@@ -0,0 +1,37 @@
+'use strict';
+
+const CastError = require('../error/cast');
+
+/*!
+ * Given a value, cast it to a string, or throw a `CastError` if the value
+ * cannot be casted. `null` and `undefined` are considered valid.
+ *
+ * @param {Any} value
+ * @param {String} [path] optional the path to set on the CastError
+ * @return {string|null|undefined}
+ * @throws {CastError}
+ * @api private
+ */
+
+module.exports = function castString(value, path) {
+  // If null or undefined
+  if (value == null) {
+    return value;
+  }
+
+  // handle documents being passed
+  if (value._id && typeof value._id === 'string') {
+    return value._id;
+  }
+
+  // Re: gh-647 and gh-3030, we're ok with casting using `toString()`
+  // **unless** its the default Object.toString, because "[object Object]"
+  // doesn't really qualify as useful data
+  if (value.toString &&
+      value.toString !== Object.prototype.toString &&
+      !Array.isArray(value)) {
+    return value.toString();
+  }
+
+  throw new CastError('string', value, path);
+};
@@ -0,0 +1,269 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const EventEmitter = require('events').EventEmitter;
+const STATES = require('./connectionstate');
+const immediate = require('./helpers/immediate');
+
+/**
+ * Abstract Collection constructor
+ *
+ * This is the base class that drivers inherit from and implement.
+ *
+ * @param {String} name name of the collection
+ * @param {Connection} conn A MongooseConnection instance
+ * @param {Object} opts optional collection options
+ * @api public
+ */
+
+function Collection(name, conn, opts) {
+  if (opts === void 0) {
+    opts = {};
+  }
+  if (opts.capped === void 0) {
+    opts.capped = {};
+  }
+
+  opts.bufferCommands = undefined === opts.bufferCommands
+    ? true
+    : opts.bufferCommands;
+
+  if (typeof opts.capped === 'number') {
+    opts.capped = {size: opts.capped};
+  }
+
+  this.opts = opts;
+  this.name = name;
+  this.collectionName = name;
+  this.conn = conn;
+  this.queue = [];
+  this.buffer = this.opts.bufferCommands;
+  this.emitter = new EventEmitter();
+
+  if (STATES.connected === this.conn.readyState) {
+    this.onOpen();
+  }
+}
+
+/**
+ * The collection name
+ *
+ * @api public
+ * @property name
+ */
+
+Collection.prototype.name;
+
+/**
+ * The collection name
+ *
+ * @api public
+ * @property collectionName
+ */
+
+Collection.prototype.collectionName;
+
+/**
+ * The Connection instance
+ *
+ * @api public
+ * @property conn
+ */
+
+Collection.prototype.conn;
+
+/**
+ * Called when the database connects
+ *
+ * @api private
+ */
+
+Collection.prototype.onOpen = function() {
+  this.buffer = false;
+  immediate(() => this.doQueue());
+};
+
+/**
+ * Called when the database disconnects
+ *
+ * @api private
+ */
+
+Collection.prototype.onClose = function(force) {
+  if (this.opts.bufferCommands && !force) {
+    this.buffer = true;
+  }
+};
+
+/**
+ * Queues a method for later execution when its
+ * database connection opens.
+ *
+ * @param {String} name name of the method to queue
+ * @param {Array} args arguments to pass to the method when executed
+ * @api private
+ */
+
+Collection.prototype.addQueue = function(name, args) {
+  this.queue.push([name, args]);
+  return this;
+};
+
+/**
+ * Executes all queued methods and clears the queue.
+ *
+ * @api private
+ */
+
+Collection.prototype.doQueue = function() {
+  for (let i = 0, l = this.queue.length; i < l; i++) {
+    if (typeof this.queue[i][0] === 'function') {
+      this.queue[i][0].apply(this, this.queue[i][1]);
+    } else {
+      this[this.queue[i][0]].apply(this, this.queue[i][1]);
+    }
+  }
+  this.queue = [];
+  const _this = this;
+  process.nextTick(function() {
+    _this.emitter.emit('queue');
+  });
+  return this;
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.ensureIndex = function() {
+  throw new Error('Collection#ensureIndex unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.createIndex = function() {
+  throw new Error('Collection#ensureIndex unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.findAndModify = function() {
+  throw new Error('Collection#findAndModify unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.findOneAndUpdate = function() {
+  throw new Error('Collection#findOneAndUpdate unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.findOneAndDelete = function() {
+  throw new Error('Collection#findOneAndDelete unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.findOneAndReplace = function() {
+  throw new Error('Collection#findOneAndReplace unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.findOne = function() {
+  throw new Error('Collection#findOne unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.find = function() {
+  throw new Error('Collection#find unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.insert = function() {
+  throw new Error('Collection#insert unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.insertOne = function() {
+  throw new Error('Collection#insertOne unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.insertMany = function() {
+  throw new Error('Collection#insertMany unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.save = function() {
+  throw new Error('Collection#save unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.update = function() {
+  throw new Error('Collection#update unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.getIndexes = function() {
+  throw new Error('Collection#getIndexes unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.mapReduce = function() {
+  throw new Error('Collection#mapReduce unimplemented by driver');
+};
+
+/**
+ * Abstract method that drivers must implement.
+ */
+
+Collection.prototype.watch = function() {
+  throw new Error('Collection#watch unimplemented by driver');
+};
+
+/*!
+ * Module exports.
+ */
+
+module.exports = Collection;
@@ -0,0 +1,26 @@
+
+/*!
+ * Connection states
+ */
+
+'use strict';
+
+const STATES = module.exports = exports = Object.create(null);
+
+const disconnected = 'disconnected';
+const connected = 'connected';
+const connecting = 'connecting';
+const disconnecting = 'disconnecting';
+const uninitialized = 'uninitialized';
+
+STATES[0] = disconnected;
+STATES[1] = connected;
+STATES[2] = connecting;
+STATES[3] = disconnecting;
+STATES[99] = uninitialized;
+
+STATES[disconnected] = 0;
+STATES[connected] = 1;
+STATES[connecting] = 2;
+STATES[disconnecting] = 3;
+STATES[uninitialized] = 99;
@@ -0,0 +1,296 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const Readable = require('stream').Readable;
+const eachAsync = require('../helpers/cursor/eachAsync');
+const util = require('util');
+const utils = require('../utils');
+
+/**
+ * An AggregationCursor is a concurrency primitive for processing aggregation
+ * results one document at a time. It is analogous to QueryCursor.
+ *
+ * An AggregationCursor fulfills the Node.js streams3 API,
+ * in addition to several other mechanisms for loading documents from MongoDB
+ * one at a time.
+ *
+ * Creating an AggregationCursor executes the model's pre aggregate hooks,
+ * but **not** the model's post aggregate hooks.
+ *
+ * Unless you're an advanced user, do **not** instantiate this class directly.
+ * Use [`Aggregate#cursor()`](/docs/api.html#aggregate_Aggregate-cursor) instead.
+ *
+ * @param {Aggregate} agg
+ * @param {Object} options
+ * @inherits Readable
+ * @event `cursor`: Emitted when the cursor is created
+ * @event `error`: Emitted when an error occurred
+ * @event `data`: Emitted when the stream is flowing and the next doc is ready
+ * @event `end`: Emitted when the stream is exhausted
+ * @api public
+ */
+
+function AggregationCursor(agg) {
+  Readable.call(this, { objectMode: true });
+
+  this.cursor = null;
+  this.agg = agg;
+  this._transforms = [];
+  const model = agg._model;
+  delete agg.options.cursor.useMongooseAggCursor;
+  this._mongooseOptions = {};
+
+  _init(model, this, agg);
+}
+
+util.inherits(AggregationCursor, Readable);
+
+/*!
+ * ignore
+ */
+
+function _init(model, c, agg) {
+  if (!model.collection.buffer) {
+    model.hooks.execPre('aggregate', agg, function() {
+      c.cursor = model.collection.aggregate(agg._pipeline, agg.options || {});
+      c.emit('cursor', c.cursor);
+    });
+  } else {
+    model.collection.emitter.once('queue', function() {
+      model.hooks.execPre('aggregate', agg, function() {
+        c.cursor = model.collection.aggregate(agg._pipeline, agg.options || {});
+        c.emit('cursor', c.cursor);
+      });
+    });
+  }
+}
+
+/*!
+ * Necessary to satisfy the Readable API
+ */
+
+AggregationCursor.prototype._read = function() {
+  const _this = this;
+  _next(this, function(error, doc) {
+    if (error) {
+      return _this.emit('error', error);
+    }
+    if (!doc) {
+      _this.push(null);
+      _this.cursor.close(function(error) {
+        if (error) {
+          return _this.emit('error', error);
+        }
+        setTimeout(function() {
+          _this.emit('close');
+        }, 0);
+      });
+      return;
+    }
+    _this.push(doc);
+  });
+};
+
+/**
+ * Registers a transform function which subsequently maps documents retrieved
+ * via the streams interface or `.next()`
+ *
+ * ####Example
+ *
+ *     // Map documents returned by `data` events
+ *     Thing.
+ *       find({ name: /^hello/ }).
+ *       cursor().
+ *       map(function (doc) {
+ *        doc.foo = "bar";
+ *        return doc;
+ *       })
+ *       on('data', function(doc) { console.log(doc.foo); });
+ *
+ *     // Or map documents returned by `.next()`
+ *     var cursor = Thing.find({ name: /^hello/ }).
+ *       cursor().
+ *       map(function (doc) {
+ *         doc.foo = "bar";
+ *         return doc;
+ *       });
+ *     cursor.next(function(error, doc) {
+ *       console.log(doc.foo);
+ *     });
+ *
+ * @param {Function} fn
+ * @return {AggregationCursor}
+ * @api public
+ * @method map
+ */
+
+AggregationCursor.prototype.map = function(fn) {
+  this._transforms.push(fn);
+  return this;
+};
+
+/*!
+ * Marks this cursor as errored
+ */
+
+AggregationCursor.prototype._markError = function(error) {
+  this._error = error;
+  return this;
+};
+
+/**
+ * Marks this cursor as closed. Will stop streaming and subsequent calls to
+ * `next()` will error.
+ *
+ * @param {Function} callback
+ * @return {Promise}
+ * @api public
+ * @method close
+ * @emits close
+ * @see MongoDB driver cursor#close http://mongodb.github.io/node-mongodb-native/2.1/api/Cursor.html#close
+ */
+
+AggregationCursor.prototype.close = function(callback) {
+  return utils.promiseOrCallback(callback, cb => {
+    this.cursor.close(error => {
+      if (error) {
+        cb(error);
+        return this.listeners('error').length > 0 && this.emit('error', error);
+      }
+      this.emit('close');
+      cb(null);
+    });
+  });
+};
+
+/**
+ * Get the next document from this cursor. Will return `null` when there are
+ * no documents left.
+ *
+ * @param {Function} callback
+ * @return {Promise}
+ * @api public
+ * @method next
+ */
+
+AggregationCursor.prototype.next = function(callback) {
+  return utils.promiseOrCallback(callback, cb => {
+    _next(this, cb);
+  });
+};
+
+/**
+ * Execute `fn` for every document in the cursor. If `fn` returns a promise,
+ * will wait for the promise to resolve before iterating on to the next one.
+ * Returns a promise that resolves when done.
+ *
+ * @param {Function} fn
+ * @param {Object} [options]
+ * @param {Number} [options.parallel] the number of promises to execute in parallel. Defaults to 1.
+ * @param {Function} [callback] executed when all docs have been processed
+ * @return {Promise}
+ * @api public
+ * @method eachAsync
+ */
+
+AggregationCursor.prototype.eachAsync = function(fn, opts, callback) {
+  const _this = this;
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  opts = opts || {};
+
+  return eachAsync(function(cb) { return _next(_this, cb); }, fn, opts, callback);
+};
+
+/*!
+ * ignore
+ */
+
+AggregationCursor.prototype.transformNull = function(val) {
+  if (arguments.length === 0) {
+    val = true;
+  }
+  this._mongooseOptions.transformNull = val;
+  return this;
+};
+
+/**
+ * Adds a [cursor flag](http://mongodb.github.io/node-mongodb-native/2.2/api/Cursor.html#addCursorFlag).
+ * Useful for setting the `noCursorTimeout` and `tailable` flags.
+ *
+ * @param {String} flag
+ * @param {Boolean} value
+ * @return {AggregationCursor} this
+ * @api public
+ * @method addCursorFlag
+ */
+
+AggregationCursor.prototype.addCursorFlag = function(flag, value) {
+  const _this = this;
+  _waitForCursor(this, function() {
+    _this.cursor.addCursorFlag(flag, value);
+  });
+  return this;
+};
+
+/*!
+ * ignore
+ */
+
+function _waitForCursor(ctx, cb) {
+  if (ctx.cursor) {
+    return cb();
+  }
+  ctx.once('cursor', function() {
+    cb();
+  });
+}
+
+/*!
+ * Get the next doc from the underlying cursor and mongooseify it
+ * (populate, etc.)
+ */
+
+function _next(ctx, cb) {
+  let callback = cb;
+  if (ctx._transforms.length) {
+    callback = function(err, doc) {
+      if (err || (doc === null && !ctx._mongooseOptions.transformNull)) {
+        return cb(err, doc);
+      }
+      cb(err, ctx._transforms.reduce(function(doc, fn) {
+        return fn(doc);
+      }, doc));
+    };
+  }
+
+  if (ctx._error) {
+    return process.nextTick(function() {
+      callback(ctx._error);
+    });
+  }
+
+  if (ctx.cursor) {
+    return ctx.cursor.next(function(error, doc) {
+      if (error) {
+        return callback(error);
+      }
+      if (!doc) {
+        return callback(null, null);
+      }
+
+      callback(null, doc);
+    });
+  } else {
+    ctx.once('cursor', function() {
+      _next(ctx, cb);
+    });
+  }
+}
+
+module.exports = AggregationCursor;
@@ -0,0 +1,58 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const EventEmitter = require('events').EventEmitter;
+
+/*!
+ * ignore
+ */
+
+class ChangeStream extends EventEmitter {
+  constructor(model, pipeline, options) {
+    super();
+
+    this.driverChangeStream = null;
+    this.closed = false;
+    // This wrapper is necessary because of buffering.
+    if (model.collection.buffer) {
+      model.collection.addQueue(() => {
+        if (this.closed) {
+          return;
+        }
+        this.driverChangeStream = model.collection.watch(pipeline, options);
+        this._bindEvents();
+        this.emit('ready');
+      });
+    } else {
+      this.driverChangeStream = model.collection.watch(pipeline, options);
+      this._bindEvents();
+      this.emit('ready');
+    }
+  }
+
+  _bindEvents() {
+    ['close', 'change', 'end', 'error'].forEach(ev => {
+      this.driverChangeStream.on(ev, data => this.emit(ev, data));
+    });
+  }
+
+  _queue(cb) {
+    this.once('ready', () => cb());
+  }
+
+  close() {
+    this.closed = true;
+    if (this.driverChangeStream) {
+      this.driverChangeStream.close();
+    }
+  }
+}
+
+/*!
+ * ignore
+ */
+
+module.exports = ChangeStream;
@@ -0,0 +1,331 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const Readable = require('stream').Readable;
+const eachAsync = require('../helpers/cursor/eachAsync');
+const helpers = require('../queryhelpers');
+const util = require('util');
+const utils = require('../utils');
+
+/**
+ * A QueryCursor is a concurrency primitive for processing query results
+ * one document at a time. A QueryCursor fulfills the Node.js streams3 API,
+ * in addition to several other mechanisms for loading documents from MongoDB
+ * one at a time.
+ *
+ * QueryCursors execute the model's pre find hooks, but **not** the model's
+ * post find hooks.
+ *
+ * Unless you're an advanced user, do **not** instantiate this class directly.
+ * Use [`Query#cursor()`](/docs/api.html#query_Query-cursor) instead.
+ *
+ * @param {Query} query
+ * @param {Object} options query options passed to `.find()`
+ * @inherits Readable
+ * @event `cursor`: Emitted when the cursor is created
+ * @event `error`: Emitted when an error occurred
+ * @event `data`: Emitted when the stream is flowing and the next doc is ready
+ * @event `end`: Emitted when the stream is exhausted
+ * @api public
+ */
+
+function QueryCursor(query, options) {
+  Readable.call(this, { objectMode: true });
+
+  this.cursor = null;
+  this.query = query;
+  const _this = this;
+  const model = query.model;
+  this._mongooseOptions = {};
+  this._transforms = [];
+  this.model = model;
+  model.hooks.execPre('find', query, () => {
+    this._transforms = this._transforms.concat(query._transforms.slice());
+    if (options.transform) {
+      this._transforms.push(options.transform);
+    }
+    model.collection.find(query._conditions, options, function(err, cursor) {
+      if (_this._error) {
+        cursor.close(function() {});
+        _this.listeners('error').length > 0 && _this.emit('error', _this._error);
+      }
+      if (err) {
+        return _this.emit('error', err);
+      }
+      _this.cursor = cursor;
+      _this.emit('cursor', cursor);
+    });
+  });
+}
+
+util.inherits(QueryCursor, Readable);
+
+/*!
+ * Necessary to satisfy the Readable API
+ */
+
+QueryCursor.prototype._read = function() {
+  const _this = this;
+  _next(this, function(error, doc) {
+    if (error) {
+      return _this.emit('error', error);
+    }
+    if (!doc) {
+      _this.push(null);
+      _this.cursor.close(function(error) {
+        if (error) {
+          return _this.emit('error', error);
+        }
+        setTimeout(function() {
+          _this.emit('close');
+        }, 0);
+      });
+      return;
+    }
+    _this.push(doc);
+  });
+};
+
+/**
+ * Registers a transform function which subsequently maps documents retrieved
+ * via the streams interface or `.next()`
+ *
+ * ####Example
+ *
+ *     // Map documents returned by `data` events
+ *     Thing.
+ *       find({ name: /^hello/ }).
+ *       cursor().
+ *       map(function (doc) {
+ *        doc.foo = "bar";
+ *        return doc;
+ *       })
+ *       on('data', function(doc) { console.log(doc.foo); });
+ *
+ *     // Or map documents returned by `.next()`
+ *     var cursor = Thing.find({ name: /^hello/ }).
+ *       cursor().
+ *       map(function (doc) {
+ *         doc.foo = "bar";
+ *         return doc;
+ *       });
+ *     cursor.next(function(error, doc) {
+ *       console.log(doc.foo);
+ *     });
+ *
+ * @param {Function} fn
+ * @return {QueryCursor}
+ * @api public
+ * @method map
+ */
+
+QueryCursor.prototype.map = function(fn) {
+  this._transforms.push(fn);
+  return this;
+};
+
+/*!
+ * Marks this cursor as errored
+ */
+
+QueryCursor.prototype._markError = function(error) {
+  this._error = error;
+  return this;
+};
+
+/**
+ * Marks this cursor as closed. Will stop streaming and subsequent calls to
+ * `next()` will error.
+ *
+ * @param {Function} callback
+ * @return {Promise}
+ * @api public
+ * @method close
+ * @emits close
+ * @see MongoDB driver cursor#close http://mongodb.github.io/node-mongodb-native/2.1/api/Cursor.html#close
+ */
+
+QueryCursor.prototype.close = function(callback) {
+  return utils.promiseOrCallback(callback, cb => {
+    this.cursor.close(error => {
+      if (error) {
+        cb(error);
+        return this.listeners('error').length > 0 && this.emit('error', error);
+      }
+      this.emit('close');
+      cb(null);
+    });
+  }, this.model.events);
+};
+
+/**
+ * Get the next document from this cursor. Will return `null` when there are
+ * no documents left.
+ *
+ * @param {Function} callback
+ * @return {Promise}
+ * @api public
+ * @method next
+ */
+
+QueryCursor.prototype.next = function(callback) {
+  return utils.promiseOrCallback(callback, cb => {
+    _next(this, function(error, doc) {
+      if (error) {
+        return cb(error);
+      }
+      cb(null, doc);
+    });
+  }, this.model.events);
+};
+
+/**
+ * Execute `fn` for every document in the cursor. If `fn` returns a promise,
+ * will wait for the promise to resolve before iterating on to the next one.
+ * Returns a promise that resolves when done.
+ *
+ * @param {Function} fn
+ * @param {Object} [options]
+ * @param {Number} [options.parallel] the number of promises to execute in parallel. Defaults to 1.
+ * @param {Function} [callback] executed when all docs have been processed
+ * @return {Promise}
+ * @api public
+ * @method eachAsync
+ */
+
+QueryCursor.prototype.eachAsync = function(fn, opts, callback) {
+  const _this = this;
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  opts = opts || {};
+
+  return eachAsync(function(cb) { return _next(_this, cb); }, fn, opts, callback);
+};
+
+/**
+ * Adds a [cursor flag](http://mongodb.github.io/node-mongodb-native/2.2/api/Cursor.html#addCursorFlag).
+ * Useful for setting the `noCursorTimeout` and `tailable` flags.
+ *
+ * @param {String} flag
+ * @param {Boolean} value
+ * @return {AggregationCursor} this
+ * @api public
+ * @method addCursorFlag
+ */
+
+QueryCursor.prototype.addCursorFlag = function(flag, value) {
+  const _this = this;
+  _waitForCursor(this, function() {
+    _this.cursor.addCursorFlag(flag, value);
+  });
+  return this;
+};
+
+/*!
+ * ignore
+ */
+
+QueryCursor.prototype.transformNull = function(val) {
+  if (arguments.length === 0) {
+    val = true;
+  }
+  this._mongooseOptions.transformNull = val;
+  return this;
+};
+
+/*!
+ * Get the next doc from the underlying cursor and mongooseify it
+ * (populate, etc.)
+ */
+
+function _next(ctx, cb) {
+  let callback = cb;
+  if (ctx._transforms.length) {
+    callback = function(err, doc) {
+      if (err || (doc === null && !ctx._mongooseOptions.transformNull)) {
+        return cb(err, doc);
+      }
+      cb(err, ctx._transforms.reduce(function(doc, fn) {
+        return fn.call(ctx, doc);
+      }, doc));
+    };
+  }
+
+  if (ctx._error) {
+    return process.nextTick(function() {
+      callback(ctx._error);
+    });
+  }
+
+  if (ctx.cursor) {
+    return ctx.cursor.next(function(error, doc) {
+      if (error) {
+        return callback(error);
+      }
+      if (!doc) {
+        return callback(null, null);
+      }
+
+      const opts = ctx.query._mongooseOptions;
+      if (!opts.populate) {
+        return opts.lean ?
+          callback(null, doc) :
+          _create(ctx, doc, null, callback);
+      }
+
+      const pop = helpers.preparePopulationOptionsMQ(ctx.query,
+        ctx.query._mongooseOptions);
+      pop.__noPromise = true;
+      ctx.query.model.populate(doc, pop, function(err, doc) {
+        if (err) {
+          return callback(err);
+        }
+        return opts.lean ?
+          callback(null, doc) :
+          _create(ctx, doc, pop, callback);
+      });
+    });
+  } else {
+    ctx.once('cursor', function() {
+      _next(ctx, cb);
+    });
+  }
+}
+
+/*!
+ * ignore
+ */
+
+function _waitForCursor(ctx, cb) {
+  if (ctx.cursor) {
+    return cb();
+  }
+  ctx.once('cursor', function() {
+    cb();
+  });
+}
+
+/*!
+ * Convert a raw doc into a full mongoose doc.
+ */
+
+function _create(ctx, doc, populatedIds, cb) {
+  const instance = helpers.createModel(ctx.query.model, doc, ctx.query._fields);
+  const opts = populatedIds ?
+    { populated: populatedIds } :
+    undefined;
+
+  instance.init(doc, opts, function(err) {
+    if (err) {
+      return cb(err);
+    }
+    cb(null, instance);
+  });
+}
+
+module.exports = QueryCursor;
@@ -32,6 +32,7 @@ const clone = utils.clone;
 const deepEqual = utils.deepEqual;
 const isMongooseObject = utils.isMongooseObject;

+const arrayAtomicsSymbol = require('./helpers/symbols').arrayAtomicsSymbol;
 const documentArrayParent = require('./helpers/symbols').documentArrayParent;
 const getSymbol = require('./helpers/symbols').getSymbol;

@@ -92,7 +93,7 @@ function Document(obj, fields, skipId, options) {

  // determine if this doc is a result of a query with
  // excluded fields
-  if (fields && utils.getFunctionName(fields.constructor) === 'Object') {
+  if (utils.isPOJO(fields)) {
    exclude = isExclusive(fields);
  }

@@ -100,13 +101,15 @@ function Document(obj, fields, skipId, options) {
    $__hasIncludedChildren(fields) :
    {};

-  this.$__buildDoc(obj, fields, skipId, exclude, hasIncludedChildren, false);
+  if (this._doc == null) {
+    this.$__buildDoc(obj, fields, skipId, exclude, hasIncludedChildren, false);

-  // By default, defaults get applied **before** setting initial values
-  // Re: gh-6155
-  $__applyDefaults(this, fields, skipId, exclude, hasIncludedChildren, true, {
-    isNew: this.isNew
-  });
+    // By default, defaults get applied **before** setting initial values
+    // Re: gh-6155
+    $__applyDefaults(this, fields, skipId, exclude, hasIncludedChildren, true, {
+      isNew: this.isNew
+    });
+  }

  if (obj) {
    if (obj instanceof Document) {
@@ -136,6 +139,7 @@ function Document(obj, fields, skipId, options) {
  }

  this.$__._id = this._id;
+  this.$locals = {};

  if (!schema.options.strict && obj) {
    const _this = this;
@@ -177,6 +181,35 @@ Document.prototype.constructor = Document;

 Document.prototype.schema;

+/**
+ * Empty object that you can use for storing properties on the document. This
+ * is handy for passing data to middleware without conflicting with Mongoose
+ * internals.
+ *
+ * ####Example:
+ *
+ *     schema.pre('save', function() {
+ *       // Mongoose will set `isNew` to `false` if `save()` succeeds
+ *       this.$locals.wasNew = this.isNew;
+ *     });
+ *
+ *     schema.post('save', function() {
+ *       // Prints true if `isNew` was set before `save()`
+ *       console.log(this.$locals.wasNew);
+ *     });
+ *
+ * @api public
+ * @property $locals
+ * @memberOf Document
+ * @instance
+ */
+
+Object.defineProperty(Document.prototype, '$locals', {
+  configurable: false,
+  enumerable: false,
+  writable: true
+});
+
 /**
 * Boolean flag specifying if the document is new.
 *
@@ -508,8 +541,7 @@ function init(self, obj, doc, prefix) {
      return;
    }

-    if (!schema && utils.isObject(obj[i]) &&
-        (!obj[i].constructor || utils.getFunctionName(obj[i].constructor) === 'Object')) {
+    if (!schema && utils.isPOJO(obj[i])) {
      // assume nested object
      if (!doc[i]) {
        doc[i] = {};
@@ -701,7 +733,7 @@ Document.prototype.$session = function $session(session) {
 */

 Document.prototype.$set = function $set(path, val, type, options) {
-  if (type && utils.getFunctionName(type.constructor) === 'Object') {
+  if (utils.isPOJO(type)) {
    options = type;
    type = undefined;
  }
@@ -759,6 +791,8 @@ Document.prototype.$set = function $set(path, val, type, options) {

      return this;
    }
+  } else {
+    this.$__.$setCalled.add(path);
  }

  function _handleIndex(i) {
@@ -777,17 +811,16 @@ Document.prototype.$set = function $set(path, val, type, options) {
      delete this._doc[key];
    }

-    if (path[key] !== null &&
-        path[key] !== void 0 &&
-        // need to know if plain object - no Buffer, ObjectId, ref, etc
-        utils.isObject(path[key]) &&
-        (!path[key].constructor || utils.getFunctionName(path[key].constructor) === 'Object') &&
+    if (typeof path[key] === 'object' &&
+        !Array.isArray(path[key]) &&
+        path[key] != null &&
        pathtype !== 'virtual' &&
        pathtype !== 'real' &&
        !(this.$__path(pathName) instanceof MixedSchema) &&
        !(this.schema.paths[pathName] &&
        this.schema.paths[pathName].options &&
        this.schema.paths[pathName].options.ref)) {
+      this.$__.$setCalled.add(prefix + key);
      this.$set(path[key], prefix + key, constructing);
    } else if (strict) {
      // Don't overwrite defaults with undefined keys (gh-3981)
@@ -824,10 +857,19 @@ Document.prototype.$set = function $set(path, val, type, options) {
    }
  }

-  const pathType = this.schema.pathType(path);
+  let pathType = this.schema.pathType(path);
+  if (pathType === 'adhocOrUndefined') {
+    pathType = getEmbeddedDiscriminatorPath(this, path, { typeOnly: true });
+  }
+
+  // Assume this is a Mongoose document that was copied into a POJO using
+  // `Object.assign()` or `{...doc}`
+  if (utils.isPOJO(val) && val.$__ != null && val._doc != null) {
+    val = val._doc;
+  }
+
  if (pathType === 'nested' && val) {
-    if (utils.isObject(val) &&
-        (!val.constructor || utils.getFunctionName(val.constructor) === 'Object')) {
+    if (typeof val === 'object' && val != null) {
      if (!merge) {
        this.setValue(path, null);
        cleanModifiedSubpaths(this, path);
@@ -851,6 +893,11 @@ Document.prototype.$set = function $set(path, val, type, options) {
  let schema;
  const parts = path.split('.');

+  // Might need to change path for top-level alias
+  if (typeof this.schema.aliases[parts[0]] == 'string') {
+    parts[0] = this.schema.aliases[parts[0]];
+  }
+
  if (pathType === 'adhocOrUndefined' && strict) {
    // check for roots that are Mixed types
    let mixed;
@@ -1020,10 +1067,7 @@ Document.prototype.$set = function $set(path, val, type, options) {
    // a single nested doc. That's to make sure we get the correct context.
    // Otherwise we would double-call the setter, see gh-7196.
    if (this.schema.singleNestedPaths[path] == null) {
-      const setterContext = constructing && this.$__.$options.priorDoc ?
-        this.$__.$options.priorDoc :
-        this;
-      val = schema.applySetters(val, setterContext, false, priorVal);
+      val = schema.applySetters(val, this, false, priorVal);
    }

    if (!didPopulate && this.$__.populated) {
@@ -1203,7 +1247,7 @@ Document.prototype.$__set = function(pathToMark, path, constructing, parts, sche
        obj[parts[i]] = val;
      }
    } else {
-      if (obj[parts[i]] && utils.getFunctionName(obj[parts[i]].constructor) === 'Object') {
+      if (utils.isPOJO(obj[parts[i]])) {
        obj = obj[parts[i]];
      } else if (obj[parts[i]] && obj[parts[i]] instanceof Embedded) {
        obj = obj[parts[i]];
@@ -1256,6 +1300,9 @@ Document.prototype.setValue = function(path, val) {
 *
 * @param {String} path
 * @param {Schema|String|Number|Buffer|*} [type] optionally specify a type for on-the-fly attributes
+ * @param {Object} [options]
+ * @param {Boolean} [options.virtuals=false] Apply virtuals before getting this path
+ * @param {Boolean} [options.getters=true] If false, skip applying getters and just get the raw value
 * @api public
 */

@@ -1277,6 +1324,11 @@ Document.prototype.get = function(path, type, options) {
    return schema.applyGetters(null, this);
  }

+  // Might need to change path for top-level alias
+  if (typeof this.schema.aliases[pieces[0]] == 'string') {
+    pieces[0] = this.schema.aliases[pieces[0]];
+  }
+
  for (let i = 0, l = pieces.length; i < l; i++) {
    if (obj && obj._doc) {
      obj = obj._doc;
@@ -1297,11 +1349,11 @@ Document.prototype.get = function(path, type, options) {
    obj = adhoc.cast(obj);
  }

-  if (schema != null) {
+  if (schema != null && options.getters !== false) {
    obj = schema.applyGetters(obj, this);
  } else if (this.schema.nested[path] && options.virtuals) {
    // Might need to apply virtuals if this is a nested path
-    return applyGetters(this, utils.clone(obj), 'virtuals', { path: path });
+    return applyGetters(this, utils.clone(obj) || {}, 'virtuals', { path: path });
  }

  return obj;
@@ -1394,6 +1446,95 @@ Document.prototype.$ignore = function(path) {
  this.$__.activePaths.ignore(path);
 };

+/**
+ * Returns the list of paths that have been directly modified. A direct
+ * modified path is a path that you explicitly set, whether via `doc.foo = 'bar'`,
+ * `Object.assign(doc, { foo: 'bar' })`, or `doc.set('foo', 'bar')`.
+ *
+ * A path `a` may be in `modifiedPaths()` but not in `directModifiedPaths()`
+ * because a child of `a` was directly modified.
+ *
+ * ####Example
+ *     const schema = new Schema({ foo: String, nested: { bar: String } });
+ *     const Model = mongoose.model('Test', schema);
+ *     await Model.create({ foo: 'original', nested: { bar: 'original' } });
+ *
+ *     const doc = await Model.findOne();
+ *     doc.nested.bar = 'modified';
+ *     doc.directModifiedPaths(); // ['nested.bar']
+ *     doc.modifiedPaths(); // ['nested', 'nested.bar']
+ *
+ * @return {Array}
+ * @api public
+ */
+
+Document.prototype.directModifiedPaths = function() {
+  return Object.keys(this.$__.activePaths.states.modify);
+};
+
+/**
+ * Returns true if the given path is nullish or only contains empty objects.
+ * Useful for determining whether this subdoc will get stripped out by the
+ * [minimize option](/docs/guide.html#minimize).
+ *
+ * ####Example:
+ *     const schema = new Schema({ nested: { foo: String } });
+ *     const Model = mongoose.model('Test', schema);
+ *     const doc = new Model({});
+ *     doc.$isEmpty('nested'); // true
+ *     doc.nested.$isEmpty(); // true
+ *
+ *     doc.nested.foo = 'bar';
+ *     doc.$isEmpty('nested'); // false
+ *     doc.nested.$isEmpty(); // false
+ *
+ * @memberOf Document
+ * @instance
+ * @api public
+ * @method $isEmpty
+ * @return {Boolean}
+ */
+
+Document.prototype.$isEmpty = function(path) {
+  const isEmptyOptions = {
+    minimize: true,
+    virtuals: false,
+    getters: false,
+    transform: false
+  };
+
+  if (arguments.length > 0) {
+    const v = this.get(path);
+    if (v == null) {
+      return true;
+    }
+    if (typeof v !== 'object') {
+      return false;
+    }
+    if (utils.isPOJO(v)) {
+      return _isEmpty(v);
+    }
+    return Object.keys(v.toObject(isEmptyOptions)).length === 0;
+  }
+
+  return Object.keys(this.toObject(isEmptyOptions)).length === 0;
+};
+
+function _isEmpty(v) {
+  if (v == null) {
+    return true;
+  }
+  if (typeof v !== 'object' || Array.isArray(v)) {
+    return false;
+  }
+  for (const key of Object.keys(v)) {
+    if (!_isEmpty(v[key])) {
+      return false;
+    }
+  }
+  return true;
+}
+
 /**
 * Returns the list of paths that have been modified.
 *
@@ -1731,7 +1872,7 @@ Document.prototype.validate = function(options, callback) {
    options = null;
  }

-  return utils.promiseOrCallback(callback, cb => this.$__validate(function(error) {
+  return utils.promiseOrCallback(callback, cb => this.$__validate(options, function(error) {
    cb(error);
  }), this.constructor.events);
 };
@@ -1784,7 +1925,8 @@ function _getPathsToValidate(doc) {
    for (i = 0; i < len; ++i) {
      subdoc = subdocs[i];
      if (doc.isModified(subdoc.$basePath, modifiedPaths) &&
-          !doc.isDirectModified(subdoc.$basePath)) {
+          !doc.isDirectModified(subdoc.$basePath) &&
+          !doc.$isDefault(subdoc.$basePath)) {
        // Remove child paths for now, because we'll be validating the whole
        // subdoc
        paths = paths.filter(function(p) {
@@ -1862,7 +2004,23 @@ function _getPathsToValidate(doc) {
 * ignore
 */

-Document.prototype.$__validate = function(callback) {
+Document.prototype.$__validate = function(options, callback) {
+  if (typeof options === 'function') {
+    callback = options;
+    options = null;
+  }
+
+  const hasValidateModifiedOnlyOption = options &&
+      (typeof options === 'object') &&
+      ('validateModifiedOnly' in options);
+
+  let shouldValidateModifiedOnly;
+  if (hasValidateModifiedOnlyOption) {
+    shouldValidateModifiedOnly = !!options.validateModifiedOnly;
+  } else {
+    shouldValidateModifiedOnly = this.schema.options.validateModifiedOnly;
+  }
+
  const _this = this;
  const _complete = () => {
    const err = this.$__.validationError;
@@ -1884,7 +2042,9 @@ Document.prototype.$__validate = function(callback) {

  // only validate required fields when necessary
  const pathDetails = _getPathsToValidate(this);
-  const paths = pathDetails[0];
+  const paths = shouldValidateModifiedOnly ?
+    pathDetails[0].filter((path) => this.isModified(path)) :
+    pathDetails[0];
  const skipSchemaValidators = pathDetails[1];

  if (paths.length === 0) {
@@ -1948,7 +2108,7 @@ Document.prototype.$__validate = function(callback) {
          _this.invalidate(path, err, undefined, true);
        }
        --total || complete();
-      }, scope, { skipSchemaValidators: skipSchemaValidators[path] });
+      }, scope, { skipSchemaValidators: skipSchemaValidators[path], path: path });
    });
  };

@@ -1975,20 +2135,33 @@ Document.prototype.$__validate = function(callback) {
 *     }
 *
 * @param {Array|string} pathsToValidate only validate the given paths
- * @return {MongooseError|undefined} MongooseError if there are errors during validation, or undefined if there is no error.
+ * @return {ValidationError|undefined} ValidationError if there are errors during validation, or undefined if there is no error.
 * @api public
 */

-Document.prototype.validateSync = function(pathsToValidate) {
+Document.prototype.validateSync = function(pathsToValidate, options) {
  const _this = this;

+  const hasValidateModifiedOnlyOption = options &&
+      (typeof options === 'object') &&
+      ('validateModifiedOnly' in options);
+
+  let shouldValidateModifiedOnly;
+  if (hasValidateModifiedOnlyOption) {
+    shouldValidateModifiedOnly = !!options.validateModifiedOnly;
+  } else {
+    shouldValidateModifiedOnly = this.schema.options.validateModifiedOnly;
+  }
+
  if (typeof pathsToValidate === 'string') {
    pathsToValidate = pathsToValidate.split(' ');
  }

  // only validate required fields when necessary
  const pathDetails = _getPathsToValidate(this);
-  let paths = pathDetails[0];
+  let paths = shouldValidateModifiedOnly ?
+    pathDetails[0].filter((path) => this.isModified(path)) :
+    pathDetails[0];
  const skipSchemaValidators = pathDetails[1];

  if (pathsToValidate && pathsToValidate.length) {
@@ -2020,7 +2193,8 @@ Document.prototype.validateSync = function(pathsToValidate) {

    const val = _this.getValue(path);
    const err = p.doValidateSync(val, _this, {
-      skipSchemaValidators: skipSchemaValidators[path]
+      skipSchemaValidators: skipSchemaValidators[path],
+      path: path
    });
    if (err && (!p.$isMongooseDocumentArray || err.$isArrayValidatorError)) {
      if (p.$isSingleNested &&
@@ -2205,9 +2379,9 @@ Document.prototype.$__reset = function reset() {
        doc.$__reset();
      }

-      _this.$__.activePaths.init(array._path);
+      _this.$__.activePaths.init(array.$path());

-      array._atomics = {};
+      array[arrayAtomicsSymbol] = {};
    });

  this.$__.activePaths.
@@ -2226,8 +2400,8 @@ Document.prototype.$__reset = function reset() {
  this.$__dirty().forEach(function(dirt) {
    const type = dirt.value;

-    if (type && type._atomics) {
-      type._atomics = {};
+    if (type && type[arrayAtomicsSymbol]) {
+      type[arrayAtomicsSymbol] = {};
    }
  });

@@ -2291,19 +2465,20 @@ Document.prototype.$__dirty = function() {
    if (!item) {
      return;
    }
-    if (item.path.indexOf(lastPath) !== 0) {
+    if (lastPath == null || item.path.indexOf(lastPath) !== 0) {
      lastPath = item.path + '.';
      minimal.push(item);
      top = item;
-    } else {
+    } else if (top != null &&
+        top.value != null &&
+        top.value[arrayAtomicsSymbol] != null &&
+        top.value.hasAtomics()) {
      // special case for top level MongooseArrays
-      if (top.value && top.value._atomics && top.value.hasAtomics()) {
-        // the `top` array itself and a sub path of `top` are being modified.
-        // the only way to honor all of both modifications is through a $set
-        // of entire array.
-        top.value._atomics = {};
-        top.value._atomics.$set = top.value;
-      }
+      // the `top` array itself and a sub path of `top` are being modified.
+      // the only way to honor all of both modifications is through a $set
+      // of entire array.
+      top.value[arrayAtomicsSymbol] = {};
+      top.value[arrayAtomicsSymbol].$set = top.value;
    }
  });

@@ -2376,22 +2551,26 @@ Document.prototype.$__getAllSubdocs = function() {
  Embedded = Embedded || require('./types/embedded');

  function docReducer(doc, seed, path) {
-    const val = path ? doc[path] : doc;
+    let val = doc;
+    if (path) {
+      if (doc instanceof Document && doc.schema.paths[path]) {
+        val = doc._doc[path];
+      } else {
+        val = doc[path];
+      }
+    }
    if (val instanceof Embedded) {
      seed.push(val);
-    }
-    else if (val instanceof Map) {
+    } else if (val instanceof Map) {
      seed = Array.from(val.keys()).reduce(function(seed, path) {
        return docReducer(val.get(path), seed, null);
      }, seed);
-    }
-    else if (val && val.$isSingleNested) {
+    } else if (val && val.$isSingleNested) {
      seed = Object.keys(val._doc).reduce(function(seed, path) {
        return docReducer(val._doc, seed, path);
      }, seed);
      seed.push(val);
-    }
-    else if (val && val.isMongooseDocumentArray) {
+    } else if (val && val.isMongooseDocumentArray) {
      val.forEach(function _docReduce(doc) {
        if (!doc || !doc._doc) {
          return;
@@ -2404,11 +2583,9 @@ Document.prototype.$__getAllSubdocs = function() {
        }, seed);
      });
    } else if (val instanceof Document && val.$__isNested) {
-      if (val) {
-        seed = Object.keys(val).reduce(function(seed, path) {
-          return docReducer(val, seed, path);
-        }, seed);
-      }
+      seed = Object.keys(val).reduce(function(seed, path) {
+        return docReducer(val, seed, path);
+      }, seed);
    }
    return seed;
  }
@@ -2479,9 +2656,7 @@ Document.prototype.$toObject = function(options, json) {
  defaultOptions = utils.options(defaultOptions, clone(schemaOptions[path] || {}));

  // If options do not exist or is not an object, set it to empty object
-  options = options && utils.getFunctionName(options.constructor) === 'Object' ?
-    clone(options) :
-    {};
+  options = utils.isPOJO(options) ? clone(options) : {};

  if (!('flattenMaps' in options)) {
    options.flattenMaps = defaultOptions.flattenMaps;
@@ -2858,8 +3033,7 @@ Document.prototype.toJSON = function(options) {
 */

 Document.prototype.inspect = function(options) {
-  const isPOJO = options &&
-    utils.getFunctionName(options.constructor) === 'Object';
+  const isPOJO = utils.isPOJO(options);
  let opts;
  if (isPOJO) {
    opts = options;
@@ -3086,7 +3260,6 @@ Document.prototype.populated = function(path, val, options) {
  }

  // internal
-
  if (val === true) {
    if (!this.$__.populated) {
      return undefined;
@@ -3096,6 +3269,22 @@ Document.prototype.populated = function(path, val, options) {

  this.$__.populated || (this.$__.populated = {});
  this.$__.populated[path] = {value: val, options: options};
+
+  // If this was a nested populate, make sure each populated doc knows
+  // about its populated children (gh-7685)
+  const pieces = path.split('.');
+  for (let i = 0; i < pieces.length - 1; ++i) {
+    const subpath = pieces.slice(0, i + 1).join('.');
+    const subdoc = this.get(subpath);
+    if (subdoc != null && subdoc.$__ != null && this.populated(subpath)) {
+      const rest = pieces.slice(i + 1).join('.');
+      subdoc.populated(rest, val, options);
+      // No need to continue because the above recursion should take care of
+      // marking the rest of the docs as populated
+      break;
+    }
+  }
+
  return val;
 };

@@ -3156,7 +3345,7 @@ Document.prototype.depopulate = function(path) {
    if (virtualKeys.indexOf(path[i]) !== -1) {
      delete this.$$populatedVirtuals[path[i]];
      delete this._doc[path[i]];
-    } else {
+    } else if (populatedIds) {
      this.$set(path[i], populatedIds);
    }
  }
@@ -0,0 +1,30 @@
+'use strict';
+
+/* eslint-env browser */
+
+/*!
+ * Module dependencies.
+ */
+const Document = require('./document.js');
+const BrowserDocument = require('./browserDocument.js');
+
+let isBrowser = false;
+
+/**
+ * Returns the Document constructor for the current context
+ *
+ * @api private
+ */
+module.exports = function() {
+  if (isBrowser) {
+    return BrowserDocument;
+  }
+  return Document;
+};
+
+/*!
+ * ignore
+ */
+module.exports.setBrowser = function(flag) {
+  isBrowser = flag;
+};
@@ -0,0 +1,15 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+let driver = null;
+
+module.exports.get = function() {
+  return driver;
+};
+
+module.exports.set = function(v) {
+  driver = v;
+};
@@ -0,0 +1,4 @@
+
+# Driver Spec
+
+TODO
@@ -0,0 +1,7 @@
+/*!
+ * ignore
+ */
+
+'use strict';
+
+module.exports = function() {};
@@ -0,0 +1,14 @@
+
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const Binary = require('bson').Binary;
+
+/*!
+ * Module exports.
+ */
+
+module.exports = exports = Binary;
@@ -0,0 +1,7 @@
+/*!
+ * ignore
+ */
+
+'use strict';
+
+module.exports = require('bson').Decimal128;
@@ -0,0 +1,13 @@
+/*!
+ * Module exports.
+ */
+
+'use strict';
+
+exports.Binary = require('./binary');
+exports.Collection = function() {
+  throw new Error('Cannot create a collection from browser library');
+};
+exports.Decimal128 = require('./decimal128');
+exports.ObjectId = require('./objectid');
+exports.ReadPreference = require('./ReadPreference');
@@ -0,0 +1,28 @@
+
+/*!
+ * [node-mongodb-native](https://github.com/mongodb/node-mongodb-native) ObjectId
+ * @constructor NodeMongoDbObjectId
+ * @see ObjectId
+ */
+
+'use strict';
+
+const ObjectId = require('bson').ObjectID;
+
+/*!
+ * Getter for convenience with populate, see gh-6115
+ */
+
+Object.defineProperty(ObjectId.prototype, '_id', {
+  enumerable: false,
+  configurable: true,
+  get: function() {
+    return this;
+  }
+});
+
+/*!
+ * ignore
+ */
+
+module.exports = exports = ObjectId;
@@ -0,0 +1,47 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const mongodb = require('mongodb');
+const ReadPref = mongodb.ReadPreference;
+
+/*!
+ * Converts arguments to ReadPrefs the driver
+ * can understand.
+ *
+ * @param {String|Array} pref
+ * @param {Array} [tags]
+ */
+
+module.exports = function readPref(pref, tags) {
+  if (Array.isArray(pref)) {
+    tags = pref[1];
+    pref = pref[0];
+  }
+
+  if (pref instanceof ReadPref) {
+    return pref;
+  }
+
+  switch (pref) {
+    case 'p':
+      pref = 'primary';
+      break;
+    case 'pp':
+      pref = 'primaryPreferred';
+      break;
+    case 's':
+      pref = 'secondary';
+      break;
+    case 'sp':
+      pref = 'secondaryPreferred';
+      break;
+    case 'n':
+      pref = 'nearest';
+      break;
+  }
+
+  return new ReadPref(pref, tags);
+};
@@ -0,0 +1,10 @@
+
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const Binary = require('mongodb').Binary;
+
+module.exports = exports = Binary;
@@ -20,8 +20,9 @@ const util = require('util');
 * @api private
 */

-function NativeCollection() {
+function NativeCollection(name, options) {
  this.collection = null;
+  this.Promise = options.Promise || Promise;
  MongooseCollection.apply(this, arguments);
 }

@@ -115,9 +116,10 @@ const syncCollectionMethods = { watch: true };
 function iter(i) {
  NativeCollection.prototype[i] = function() {
    const collection = this.collection;
-    const args = arguments;
+    const args = Array.from(arguments);
    const _this = this;
    const debug = get(_this, 'conn.base.options.debug');
+    const lastArg = arguments[arguments.length - 1];

    // If user force closed, queueing will hang forever. See #5664
    if (this.opts.$wasForceClosed) {
@@ -127,8 +129,18 @@ function iter(i) {
      if (syncCollectionMethods[i]) {
        throw new Error('Collection method ' + i + ' is synchronous');
      }
-      this.addQueue(i, arguments);
-      return;
+      if (typeof lastArg === 'function') {
+        this.addQueue(i, args);
+        return;
+      }
+      return new this.Promise((resolve, reject) => {
+        this.addQueue(i, [].concat(args).concat([(err, res) => {
+          if (err != null) {
+            return reject(err);
+          }
+          resolve(res);
+        }]));
+      });
    }

    if (debug) {
@@ -0,0 +1,181 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseConnection = require('../../connection');
+const STATES = require('../../connectionstate');
+
+/**
+ * A [node-mongodb-native](https://github.com/mongodb/node-mongodb-native) connection implementation.
+ *
+ * @inherits Connection
+ * @api private
+ */
+
+function NativeConnection() {
+  MongooseConnection.apply(this, arguments);
+  this._listening = false;
+}
+
+/**
+ * Expose the possible connection states.
+ * @api public
+ */
+
+NativeConnection.STATES = STATES;
+
+/*!
+ * Inherits from Connection.
+ */
+
+NativeConnection.prototype.__proto__ = MongooseConnection.prototype;
+
+/**
+ * Switches to a different database using the same connection pool.
+ *
+ * Returns a new connection object, with the new db.
+ *
+ * @param {String} name The database name
+ * @return {Connection} New Connection Object
+ * @api public
+ */
+
+NativeConnection.prototype.useDb = function(name, options) {
+  // Return immediately if cached
+  if (options && options.useCache && this.relatedDbs[name]) {
+    return this.relatedDbs[name];
+  }
+
+  // we have to manually copy all of the attributes...
+  const newConn = new this.constructor();
+  newConn.name = name;
+  newConn.base = this.base;
+  newConn.collections = {};
+  newConn.models = {};
+  newConn.replica = this.replica;
+  newConn.name = this.name;
+  newConn.options = this.options;
+  newConn._readyState = this._readyState;
+  newConn._closeCalled = this._closeCalled;
+  newConn._hasOpened = this._hasOpened;
+  newConn._listening = false;
+
+  newConn.host = this.host;
+  newConn.port = this.port;
+  newConn.user = this.user;
+  newConn.pass = this.pass;
+
+  // First, when we create another db object, we are not guaranteed to have a
+  // db object to work with. So, in the case where we have a db object and it
+  // is connected, we can just proceed with setting everything up. However, if
+  // we do not have a db or the state is not connected, then we need to wait on
+  // the 'open' event of the connection before doing the rest of the setup
+  // the 'connected' event is the first time we'll have access to the db object
+
+  const _this = this;
+
+  newConn.client = _this.client;
+
+  if (this.db && this._readyState === STATES.connected) {
+    wireup();
+  } else {
+    this.once('connected', wireup);
+  }
+
+  function wireup() {
+    newConn.client = _this.client;
+    newConn.db = _this.client.db(name);
+    newConn.onOpen();
+    // setup the events appropriately
+    listen(newConn);
+  }
+
+  newConn.name = name;
+
+  // push onto the otherDbs stack, this is used when state changes
+  this.otherDbs.push(newConn);
+  newConn.otherDbs.push(this);
+
+  // push onto the relatedDbs cache, this is used when state changes
+  if (options && options.useCache) {
+    this.relatedDbs[newConn.name] = newConn;
+    newConn.relatedDbs = this.relatedDbs;
+  }
+
+  return newConn;
+};
+
+/*!
+ * Register listeners for important events and bubble appropriately.
+ */
+
+function listen(conn) {
+  if (conn.db._listening) {
+    return;
+  }
+  conn.db._listening = true;
+
+  conn.db.on('close', function(force) {
+    if (conn._closeCalled) return;
+
+    // the driver never emits an `open` event. auto_reconnect still
+    // emits a `close` event but since we never get another
+    // `open` we can't emit close
+    if (conn.db.serverConfig.autoReconnect) {
+      conn.readyState = STATES.disconnected;
+      conn.emit('close');
+      return;
+    }
+    conn.onClose(force);
+  });
+  conn.db.on('error', function(err) {
+    conn.emit('error', err);
+  });
+  conn.db.on('reconnect', function() {
+    conn.readyState = STATES.connected;
+    conn.emit('reconnect');
+    conn.emit('reconnected');
+    conn.onOpen();
+  });
+  conn.db.on('timeout', function(err) {
+    conn.emit('timeout', err);
+  });
+  conn.db.on('open', function(err, db) {
+    if (STATES.disconnected === conn.readyState && db && db.databaseName) {
+      conn.readyState = STATES.connected;
+      conn.emit('reconnect');
+      conn.emit('reconnected');
+    }
+  });
+  conn.db.on('parseError', function(err) {
+    conn.emit('parseError', err);
+  });
+}
+
+/**
+ * Closes the connection
+ *
+ * @param {Boolean} [force]
+ * @param {Function} [fn]
+ * @return {Connection} this
+ * @api private
+ */
+
+NativeConnection.prototype.doClose = function(force, fn) {
+  this.client.close(force, (err, res) => {
+    // Defer because the driver will wait at least 1ms before finishing closing
+    // the pool, see https://github.com/mongodb-js/mongodb-core/blob/a8f8e4ce41936babc3b9112bf42d609779f03b39/lib/connection/pool.js#L1026-L1030.
+    // If there's queued operations, you may still get some background work
+    // after the callback is called.
+    setTimeout(() => fn(err, res), 1);
+  });
+  return this;
+};
+
+/*!
+ * Module exports.
+ */
+
+module.exports = NativeConnection;
@@ -0,0 +1,7 @@
+/*!
+ * ignore
+ */
+
+'use strict';
+
+module.exports = require('mongodb').Decimal128;
@@ -0,0 +1,11 @@
+/*!
+ * Module exports.
+ */
+
+'use strict';
+
+exports.Binary = require('./binary');
+exports.Collection = require('./collection');
+exports.Decimal128 = require('./decimal128');
+exports.ObjectId = require('./objectid');
+exports.ReadPreference = require('./ReadPreference');
@@ -0,0 +1,16 @@
+
+/*!
+ * [node-mongodb-native](https://github.com/mongodb/node-mongodb-native) ObjectId
+ * @constructor NodeMongoDbObjectId
+ * @see ObjectId
+ */
+
+'use strict';
+
+const ObjectId = require('mongodb').ObjectId;
+
+/*!
+ * ignore
+ */
+
+module.exports = exports = ObjectId;
@@ -0,0 +1,38 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/*!
+ * MissingSchema Error constructor.
+ *
+ * @inherits MongooseError
+ */
+
+function MissingSchemaError() {
+  const msg = 'Schema hasn\'t been registered for document.\n'
+          + 'Use mongoose.Document(name, schema)';
+  MongooseError.call(this, msg);
+  this.name = 'MissingSchemaError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+MissingSchemaError.prototype = Object.create(MongooseError.prototype);
+MissingSchemaError.prototype.constructor = MongooseError;
+
+/*!
+ * exports
+ */
+
+module.exports = MissingSchemaError;
@@ -0,0 +1,62 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const MongooseError = require('./mongooseError');
+const util = require('util');
+
+/**
+ * Casting Error constructor.
+ *
+ * @param {String} type
+ * @param {String} value
+ * @inherits MongooseError
+ * @api private
+ */
+
+function CastError(type, value, path, reason) {
+  let stringValue = util.inspect(value);
+  stringValue = stringValue.replace(/^'/, '"').replace(/'$/, '"');
+  if (stringValue.charAt(0) !== '"') {
+    stringValue = '"' + stringValue + '"';
+  }
+  MongooseError.call(this, 'Cast to ' + type + ' failed for value ' +
+    stringValue + ' at path "' + path + '"');
+  this.name = 'CastError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+  this.stringValue = stringValue;
+  this.kind = type;
+  this.value = value;
+  this.path = path;
+  this.reason = reason;
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+CastError.prototype = Object.create(MongooseError.prototype);
+CastError.prototype.constructor = MongooseError;
+
+/*!
+ * ignore
+ */
+
+CastError.prototype.setModel = function(model) {
+  this.model = model;
+  this.message = 'Cast to ' + this.kind + ' failed for value ' +
+    this.stringValue + ' at path "' + this.path + '"' + ' for model "' +
+    model.modelName + '"';
+};
+
+/*!
+ * exports
+ */
+
+module.exports = CastError;
@@ -0,0 +1,43 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/**
+ * The connection failed to reconnect and will never successfully reconnect to
+ * MongoDB without manual intervention.
+ *
+ * @param {String} type
+ * @param {String} value
+ * @inherits MongooseError
+ * @api private
+ */
+
+function DisconnectedError(connectionString) {
+  MongooseError.call(this, 'Ran out of retries trying to reconnect to "' +
+    connectionString + '". Try setting `server.reconnectTries` and ' +
+    '`server.reconnectInterval` to something higher.');
+  this.name = 'DisconnectedError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+DisconnectedError.prototype = Object.create(MongooseError.prototype);
+DisconnectedError.prototype.constructor = MongooseError;
+
+
+/*!
+ * exports
+ */
+
+module.exports = DisconnectedError;
@@ -0,0 +1,48 @@
+
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/*!
+ * DivergentArrayError constructor.
+ *
+ * @inherits MongooseError
+ */
+
+function DivergentArrayError(paths) {
+  const msg = 'For your own good, using `document.save()` to update an array '
+          + 'which was selected using an $elemMatch projection OR '
+          + 'populated using skip, limit, query conditions, or exclusion of '
+          + 'the _id field when the operation results in a $pop or $set of '
+          + 'the entire array is not supported. The following '
+          + 'path(s) would have been modified unsafely:\n'
+          + '  ' + paths.join('\n  ') + '\n'
+          + 'Use Model.update() to update these arrays instead.';
+  // TODO write up a docs page (FAQ) and link to it
+
+  MongooseError.call(this, msg);
+  this.name = 'DivergentArrayError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+DivergentArrayError.prototype = Object.create(MongooseError.prototype);
+DivergentArrayError.prototype.constructor = MongooseError;
+
+
+/*!
+ * exports
+ */
+
+module.exports = DivergentArrayError;
@@ -0,0 +1,106 @@
+'use strict';
+
+const MongooseError = require('./mongooseError');
+
+/*!
+ * Module exports.
+ */
+
+module.exports = exports = MongooseError;
+
+/**
+ * The default built-in validator error messages.
+ *
+ * @see Error.messages #error_messages_MongooseError-messages
+ * @api public
+ */
+
+MongooseError.messages = require('./messages');
+
+// backward compat
+MongooseError.Messages = MongooseError.messages;
+
+/**
+ * An instance of this error class will be returned when `save()` fails
+ * because the underlying
+ * document was not found. The constructor takes one parameter, the
+ * conditions that mongoose passed to `update()` when trying to update
+ * the document.
+ *
+ * @api public
+ */
+
+MongooseError.DocumentNotFoundError = require('./notFound');
+
+/**
+ * An instance of this error class will be returned when mongoose failed to
+ * cast a value.
+ *
+ * @api public
+ */
+
+MongooseError.CastError = require('./cast');
+
+/**
+ * An instance of this error class will be returned when [validation](/docs/validation.html) failed.
+ * The `errors` property contains an object whose keys are the paths that failed and whose values are
+ * instances of CastError or ValidationError.
+ *
+ * @api public
+ */
+
+MongooseError.ValidationError = require('./validation');
+
+/**
+ * A `ValidationError` has a hash of `errors` that contain individual `ValidatorError` instances
+ *
+ * @api public
+ */
+
+MongooseError.ValidatorError = require('./validator');
+
+/**
+ * An instance of this error class will be returned when you call `save()` after
+ * the document in the database was changed in a potentially unsafe way. See
+ * the [`versionKey` option](/docs/guide.html#versionKey) for more information.
+ *
+ * @api public
+ */
+
+MongooseError.VersionError = require('./version');
+
+/**
+ * An instance of this error class will be returned when you call `save()` multiple
+ * times on the same document in parallel. See the [FAQ](/docs/faq.html) for more
+ * information.
+ *
+ * @api public
+ */
+
+MongooseError.ParallelSaveError = require('./parallelSave');
+
+/**
+ * Thrown when a model with the given name was already registered on the connection.
+ * See [the FAQ about `OverwriteModelError`](/docs/faq.html#overwrite-model-error).
+ *
+ * @api public
+ */
+
+MongooseError.OverwriteModelError = require('./overwriteModel');
+
+/**
+ * Thrown when you try to access a model that has not been registered yet
+ *
+ * @api public
+ */
+
+MongooseError.MissingSchemaError = require('./missingSchema');
+
+/**
+ * An instance of this error will be returned if you used an array projection
+ * and then modified the array in an unsafe way.
+ *
+ * @api public
+ */
+
+MongooseError.DivergentArrayError = require('./divergentArray');
@@ -0,0 +1,46 @@
+
+/**
+ * The default built-in validator error messages. These may be customized.
+ *
+ *     // customize within each schema or globally like so
+ *     var mongoose = require('mongoose');
+ *     mongoose.Error.messages.String.enum  = "Your custom message for {PATH}.";
+ *
+ * As you might have noticed, error messages support basic templating
+ *
+ * - `{PATH}` is replaced with the invalid document path
+ * - `{VALUE}` is replaced with the invalid value
+ * - `{TYPE}` is replaced with the validator type such as "regexp", "min", or "user defined"
+ * - `{MIN}` is replaced with the declared min value for the Number.min validator
+ * - `{MAX}` is replaced with the declared max value for the Number.max validator
+ *
+ * Click the "show code" link below to see all defaults.
+ *
+ * @static messages
+ * @receiver MongooseError
+ * @api public
+ */
+
+'use strict';
+
+const msg = module.exports = exports = {};
+
+msg.DocumentNotFoundError = null;
+
+msg.general = {};
+msg.general.default = 'Validator failed for path `{PATH}` with value `{VALUE}`';
+msg.general.required = 'Path `{PATH}` is required.';
+
+msg.Number = {};
+msg.Number.min = 'Path `{PATH}` ({VALUE}) is less than minimum allowed value ({MIN}).';
+msg.Number.max = 'Path `{PATH}` ({VALUE}) is more than maximum allowed value ({MAX}).';
+
+msg.Date = {};
+msg.Date.min = 'Path `{PATH}` ({VALUE}) is before minimum allowed value ({MIN}).';
+msg.Date.max = 'Path `{PATH}` ({VALUE}) is after maximum allowed value ({MAX}).';
+
+msg.String = {};
+msg.String.enum = '`{VALUE}` is not a valid enum value for path `{PATH}`.';
+msg.String.match = 'Path `{PATH}` is invalid ({VALUE}).';
+msg.String.minlength = 'Path `{PATH}` (`{VALUE}`) is shorter than the minimum allowed length ({MINLENGTH}).';
+msg.String.maxlength = 'Path `{PATH}` (`{VALUE}`) is longer than the maximum allowed length ({MAXLENGTH}).';
@@ -0,0 +1,39 @@
+
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/*!
+ * MissingSchema Error constructor.
+ *
+ * @inherits MongooseError
+ */
+
+function MissingSchemaError(name) {
+  const msg = 'Schema hasn\'t been registered for model "' + name + '".\n'
+          + 'Use mongoose.model(name, schema)';
+  MongooseError.call(this, msg);
+  this.name = 'MissingSchemaError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+MissingSchemaError.prototype = Object.create(MongooseError.prototype);
+MissingSchemaError.prototype.constructor = MongooseError;
+
+/*!
+ * exports
+ */
+
+module.exports = MissingSchemaError;
@@ -0,0 +1,55 @@
+'use strict';
+
+/**
+ * MongooseError constructor. MongooseError is the base class for all
+ * Mongoose-specific errors.
+ *
+ * @param {String} msg Error message
+ * @inherits Error https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Error
+ */
+
+function MongooseError(msg) {
+  Error.call(this);
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+  this.message = msg;
+  this.name = 'MongooseError';
+}
+
+/*!
+ * Inherits from Error.
+ */
+
+MongooseError.prototype = Object.create(Error.prototype);
+MongooseError.prototype.constructor = Error;
+
+/**
+ * The name of the error. The name uniquely identifies this Mongoose error. The
+ * possible values are:
+ *
+ * - `MongooseError`: general Mongoose error
+ * - `CastError`: Mongoose could not convert a value to the type defined in the schema path. May be in a `ValidationError` class' `errors` property.
+ * - `DisconnectedError`: This [connection](connections.html) timed out in trying to reconnect to MongoDB and will not successfully reconnect to MongoDB unless you explicitly reconnect.
+ * - `DivergentArrayError`: You attempted to `save()` an array that was modified after you loaded it with a `$elemMatch` or similar projection
+ * - `MissingSchemaError`: You tried to access a model with [`mongoose.model()`](api.html#mongoose_Mongoose-model) that was not defined
+ * - `DocumentNotFoundError`: The document you tried to [`save()`](api.html#document_Document-save) was not found
+ * - `ValidatorError`: error from an individual schema path's validator
+ * - `ValidationError`: error returned from [`validate()`](api.html#document_Document-validate) or [`validateSync()`](api.html#document_Document-validateSync). Contains zero or more `ValidatorError` instances in `.errors` property.
+ * - `MissingSchemaError`: You called `mongoose.Document()` without a schema
+ * - `ObjectExpectedError`: Thrown when you set a nested path to a non-object value with [strict mode set](guide.html#strict).
+ * - `ObjectParameterError`: Thrown when you pass a non-object value to a function which expects an object as a paramter
+ * - `OverwriteModelError`: Thrown when you call [`mongoose.model()`](api.html#mongoose_Mongoose-model) to re-define a model that was already defined.
+ * - `ParallelSaveError`: Thrown when you call [`save()`](api.html#model_Model-save) on a document when the same document instance is already saving.
+ * - `StrictModeError`: Thrown when you set a path that isn't the schema and [strict mode](guide.html#strict) is set to `throw`.
+ * - `VersionError`: Thrown when the [document is out of sync](guide.html#versionKey)
+ *
+ * @api public
+ * @property {String} name
+ * @memberOf MongooseError
+ * @instance
+ */
+
+module.exports = MongooseError;
@@ -0,0 +1,38 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/**
+ * Strict mode error constructor
+ *
+ * @param {String} type
+ * @param {String} value
+ * @inherits MongooseError
+ * @api private
+ */
+
+function ObjectExpectedError(path, val) {
+  const typeDescription = Array.isArray(val) ? 'array' : 'primitive value';
+  MongooseError.call(this, 'Tried to set nested object field `' + path +
+    `\` to ${typeDescription} \`` + val + '` and strict mode is set to throw.');
+  this.name = 'ObjectExpectedError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+  this.path = path;
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+ObjectExpectedError.prototype = Object.create(MongooseError.prototype);
+ObjectExpectedError.prototype.constructor = MongooseError;
+
+module.exports = ObjectExpectedError;
@@ -0,0 +1,38 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/**
+ * Constructor for errors that happen when a parameter that's expected to be
+ * an object isn't an object
+ *
+ * @param {Any} value
+ * @param {String} paramName
+ * @param {String} fnName
+ * @inherits MongooseError
+ * @api private
+ */
+
+function ObjectParameterError(value, paramName, fnName) {
+  MongooseError.call(this, 'Parameter "' + paramName + '" to ' + fnName +
+    '() must be an object, got ' + value.toString());
+  this.name = 'ObjectParameterError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+ObjectParameterError.prototype = Object.create(MongooseError.prototype);
+ObjectParameterError.prototype.constructor = MongooseError;
+
+module.exports = ObjectParameterError;
@@ -0,0 +1,37 @@
+
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/*!
+ * OverwriteModel Error constructor.
+ *
+ * @inherits MongooseError
+ */
+
+function OverwriteModelError(name) {
+  MongooseError.call(this, 'Cannot overwrite `' + name + '` model once compiled.');
+  this.name = 'OverwriteModelError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+OverwriteModelError.prototype = Object.create(MongooseError.prototype);
+OverwriteModelError.prototype.constructor = MongooseError;
+
+/*!
+ * exports
+ */
+
+module.exports = OverwriteModelError;
@@ -0,0 +1,33 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const MongooseError = require('./');
+
+/**
+ * ParallelSave Error constructor.
+ *
+ * @inherits MongooseError
+ * @api private
+ */
+
+function ParallelSaveError(doc) {
+  const msg = 'Can\'t save() the same doc multiple times in parallel. Document: ';
+  MongooseError.call(this, msg + doc.id);
+  this.name = 'ParallelSaveError';
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+ParallelSaveError.prototype = Object.create(MongooseError.prototype);
+ParallelSaveError.prototype.constructor = MongooseError;
+
+/*!
+ * exports
+ */
+
+module.exports = ParallelSaveError;
@@ -0,0 +1,38 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/**
+ * Strict mode error constructor
+ *
+ * @param {String} type
+ * @param {String} value
+ * @inherits MongooseError
+ * @api private
+ */
+
+function StrictModeError(path, msg) {
+  msg = msg || 'Field `' + path + '` is not in schema and strict ' +
+    'mode is set to throw.';
+  MongooseError.call(this, msg);
+  this.name = 'StrictModeError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+  this.path = path;
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+StrictModeError.prototype = Object.create(MongooseError.prototype);
+StrictModeError.prototype.constructor = MongooseError;
+
+module.exports = StrictModeError;
@@ -0,0 +1,112 @@
+/*!
+ * Module requirements
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+const util = require('util');
+
+/**
+ * Document Validation Error
+ *
+ * @api private
+ * @param {Document} instance
+ * @inherits MongooseError
+ */
+
+function ValidationError(instance) {
+  this.errors = {};
+  this._message = '';
+  if (instance && instance.constructor.name === 'model') {
+    this._message = instance.constructor.modelName + ' validation failed';
+    MongooseError.call(this, this._message);
+  } else {
+    this._message = 'Validation failed';
+    MongooseError.call(this, this._message);
+  }
+  this.name = 'ValidationError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+  if (instance) {
+    instance.errors = this.errors;
+  }
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+ValidationError.prototype = Object.create(MongooseError.prototype);
+ValidationError.prototype.constructor = MongooseError;
+
+/**
+ * Console.log helper
+ */
+
+ValidationError.prototype.toString = function() {
+  return this.name + ': ' + _generateMessage(this);
+};
+
+/*!
+ * inspect helper
+ */
+
+ValidationError.prototype.inspect = function() {
+  return Object.assign(new Error(this.message), this);
+};
+
+if (util.inspect.custom) {
+  /*!
+  * Avoid Node deprecation warning DEP0079
+  */
+
+  ValidationError.prototype[util.inspect.custom] = ValidationError.prototype.inspect;
+}
+
+/*!
+ * Helper for JSON.stringify
+ */
+
+ValidationError.prototype.toJSON = function() {
+  return Object.assign({}, this, { message: this.message });
+};
+
+/*!
+ * add message
+ */
+
+ValidationError.prototype.addError = function(path, error) {
+  this.errors[path] = error;
+  this.message = this._message + ': ' + _generateMessage(this);
+};
+
+/*!
+ * ignore
+ */
+
+function _generateMessage(err) {
+  const keys = Object.keys(err.errors || {});
+  const len = keys.length;
+  const msgs = [];
+  let key;
+
+  for (let i = 0; i < len; ++i) {
+    key = keys[i];
+    if (err === err.errors[key]) {
+      continue;
+    }
+    msgs.push(key + ': ' + err.errors[key].message);
+  }
+
+  return msgs.join(', ');
+}
+
+/*!
+ * Module exports
+ */
+
+module.exports = exports = ValidationError;
@@ -0,0 +1,89 @@
+/*!
+ * Module dependencies.
+ */
+
+'use strict';
+
+const MongooseError = require('./');
+
+/**
+ * Schema validator error
+ *
+ * @param {Object} properties
+ * @inherits MongooseError
+ * @api private
+ */
+
+function ValidatorError(properties) {
+  let msg = properties.message;
+  if (!msg) {
+    msg = MongooseError.messages.general.default;
+  }
+
+  const message = this.formatMessage(msg, properties);
+  MongooseError.call(this, message);
+
+  properties = Object.assign({}, properties, { message: message });
+  this.name = 'ValidatorError';
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this);
+  } else {
+    this.stack = new Error().stack;
+  }
+  this.properties = properties;
+  this.kind = properties.type;
+  this.path = properties.path;
+  this.value = properties.value;
+  this.reason = properties.reason;
+}
+
+/*!
+ * Inherits from MongooseError
+ */
+
+ValidatorError.prototype = Object.create(MongooseError.prototype);
+ValidatorError.prototype.constructor = MongooseError;
+
+/*!
+ * The object used to define this validator. Not enumerable to hide
+ * it from `require('util').inspect()` output re: gh-3925
+ */
+
+Object.defineProperty(ValidatorError.prototype, 'properties', {
+  enumerable: false,
+  writable: true,
+  value: null
+});
+
+/*!
+ * Formats error messages
+ */
+
+ValidatorError.prototype.formatMessage = function(msg, properties) {
+  if (typeof msg === 'function') {
+    return msg(properties);
+  }
+  const propertyNames = Object.keys(properties);
+  for (let i = 0; i < propertyNames.length; ++i) {
+    const propertyName = propertyNames[i];
+    if (propertyName === 'message') {
+      continue;
+    }
+    msg = msg.replace('{' + propertyName.toUpperCase() + '}', properties[propertyName]);
+  }
+  return msg;
+};
+
+/*!
+ * toString helper
+ */
+
+ValidatorError.prototype.toString = function() {
+  return this.message;
+};
+
+/*!
+ * exports
+ */
+
+module.exports = ValidatorError;
@@ -0,0 +1,36 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const MongooseError = require('./');
+
+/**
+ * Version Error constructor.
+ *
+ * @inherits MongooseError
+ * @api private
+ */
+
+function VersionError(doc, currentVersion, modifiedPaths) {
+  const modifiedPathsStr = modifiedPaths.join(', ');
+  MongooseError.call(this, 'No matching document found for id "' + doc._id +
+    '" version ' + currentVersion + ' modifiedPaths "' + modifiedPathsStr + '"');
+  this.name = 'VersionError';
+  this.version = currentVersion;
+  this.modifiedPaths = modifiedPaths;
+}
+
+/*!
+ * Inherits from MongooseError.
+ */
+
+VersionError.prototype = Object.create(MongooseError.prototype);
+VersionError.prototype.constructor = MongooseError;
+
+/*!
+ * exports
+ */
+
+module.exports = VersionError;
@@ -0,0 +1,89 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const Decimal128 = require('../types/decimal128');
+const ObjectId = require('../types/objectid');
+const utils = require('../utils');
+
+exports.flatten = flatten;
+exports.modifiedPaths = modifiedPaths;
+
+/*!
+ * ignore
+ */
+
+function flatten(update, path, options) {
+  let keys;
+  if (update && utils.isMongooseObject(update) && !Buffer.isBuffer(update)) {
+    keys = Object.keys(update.toObject({ transform: false, virtuals: false }));
+  } else {
+    keys = Object.keys(update || {});
+  }
+
+  const numKeys = keys.length;
+  const result = {};
+  path = path ? path + '.' : '';
+
+  for (let i = 0; i < numKeys; ++i) {
+    const key = keys[i];
+    const val = update[key];
+    result[path + key] = val;
+    if (shouldFlatten(val)) {
+      if (options && options.skipArrays && Array.isArray(val)) {
+        continue;
+      }
+      const flat = flatten(val, path + key, options);
+      for (const k in flat) {
+        result[k] = flat[k];
+      }
+      if (Array.isArray(val)) {
+        result[path + key] = val;
+      }
+    }
+  }
+
+  return result;
+}
+
+/*!
+ * ignore
+ */
+
+function modifiedPaths(update, path, result) {
+  const keys = Object.keys(update || {});
+  const numKeys = keys.length;
+  result = result || {};
+  path = path ? path + '.' : '';
+
+  for (let i = 0; i < numKeys; ++i) {
+    const key = keys[i];
+    let val = update[key];
+
+    result[path + key] = true;
+    if (utils.isMongooseObject(val) && !Buffer.isBuffer(val)) {
+      val = val.toObject({ transform: false, virtuals: false });
+    }
+    if (shouldFlatten(val)) {
+      modifiedPaths(val, path + key, result);
+    }
+  }
+
+  return result;
+}
+
+/*!
+ * ignore
+ */
+
+function shouldFlatten(val) {
+  return val &&
+    typeof val === 'object' &&
+    !(val instanceof Date) &&
+    !(val instanceof ObjectId) &&
+    (!Array.isArray(val) || val.length > 0) &&
+    !(val instanceof Buffer) &&
+    !(val instanceof Decimal128);
+}
@@ -0,0 +1,71 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const async = require('async');
+const utils = require('../../utils');
+
+/**
+ * Execute `fn` for every document in the cursor. If `fn` returns a promise,
+ * will wait for the promise to resolve before iterating on to the next one.
+ * Returns a promise that resolves when done.
+ *
+ * @param {Function} next the thunk to call to get the next document
+ * @param {Function} fn
+ * @param {Object} options
+ * @param {Function} [callback] executed when all docs have been processed
+ * @return {Promise}
+ * @api public
+ * @method eachAsync
+ */
+
+module.exports = function eachAsync(next, fn, options, callback) {
+  const parallel = options.parallel || 1;
+
+  const handleNextResult = function(doc, callback) {
+    const promise = fn(doc);
+    if (promise && typeof promise.then === 'function') {
+      promise.then(
+        function() { callback(null); },
+        function(error) { callback(error || new Error('`eachAsync()` promise rejected without error')); });
+    } else {
+      callback(null);
+    }
+  };
+
+  const iterate = function(callback) {
+    let drained = false;
+    const nextQueue = async.queue(function(task, cb) {
+      if (drained) return cb();
+      next(function(err, doc) {
+        if (err) return cb(err);
+        if (!doc) drained = true;
+        cb(null, doc);
+      });
+    }, 1);
+
+    const getAndRun = function(cb) {
+      nextQueue.push({}, function(err, doc) {
+        if (err) return cb(err);
+        if (!doc) return cb();
+        handleNextResult(doc, function(err) {
+          if (err) return cb(err);
+          // Make sure to clear the stack re: gh-4697
+          setTimeout(function() {
+            getAndRun(cb);
+          }, 0);
+        });
+      });
+    };
+
+    async.times(parallel, function(n, cb) {
+      getAndRun(cb);
+    }, callback);
+  };
+
+  return utils.promiseOrCallback(callback, cb => {
+    iterate(cb);
+  });
+};
@@ -0,0 +1,12 @@
+'use strict';
+
+module.exports = function checkEmbeddedDiscriminatorKeyProjection(userProjection, path, schema, selected, addedPaths) {
+  const userProjectedInPath = Object.keys(userProjection).
+    reduce((cur, key) => cur || key.startsWith(path + '.'), false);
+  const _discriminatorKey = path + '.' + schema.options.discriminatorKey;
+  if (!userProjectedInPath &&
+      addedPaths.length === 1 &&
+      addedPaths[0] === _discriminatorKey) {
+    selected.splice(selected.indexOf(_discriminatorKey), 1);
+  }
+};
@@ -0,0 +1,28 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = function cleanModifiedSubpaths(doc, path, options) {
+  options = options || {};
+  const skipDocArrays = options.skipDocArrays;
+
+  let deleted = 0;
+  if (!doc) {
+    return deleted;
+  }
+  for (const modifiedPath of Object.keys(doc.$__.activePaths.states.modify)) {
+    if (skipDocArrays) {
+      const schemaType = doc.schema.path(modifiedPath);
+      if (schemaType && schemaType.$isMongooseDocumentArray) {
+        continue;
+      }
+    }
+    if (modifiedPath.indexOf(path + '.') === 0) {
+      delete doc.$__.activePaths.states.modify[modifiedPath];
+      ++deleted;
+    }
+  }
+  return deleted;
+};
@@ -0,0 +1,162 @@
+'use strict';
+
+const get = require('../../helpers/get');
+const getSymbol = require('../../helpers/symbols').getSymbol;
+const utils = require('../../utils');
+
+let Document;
+
+/*!
+ * exports
+ */
+
+exports.compile = compile;
+exports.defineKey = defineKey;
+
+/*!
+ * Compiles schemas.
+ */
+
+function compile(tree, proto, prefix, options) {
+  Document = Document || require('../../document');
+  const keys = Object.keys(tree);
+  const len = keys.length;
+  let limb;
+  let key;
+
+  for (let i = 0; i < len; ++i) {
+    key = keys[i];
+    limb = tree[key];
+
+    const hasSubprops = utils.isPOJO(limb) && Object.keys(limb).length &&
+      (!limb[options.typeKey] || (options.typeKey === 'type' && limb.type.type));
+    const subprops = hasSubprops ? limb : null;
+
+    defineKey(key, subprops, proto, prefix, keys, options);
+  }
+}
+
+/*!
+ * Defines the accessor named prop on the incoming prototype.
+ */
+
+function defineKey(prop, subprops, prototype, prefix, keys, options) {
+  Document = Document || require('../../document');
+  const path = (prefix ? prefix + '.' : '') + prop;
+  prefix = prefix || '';
+
+  if (subprops) {
+    Object.defineProperty(prototype, prop, {
+      enumerable: true,
+      configurable: true,
+      get: function() {
+        const _this = this;
+        if (!this.$__.getters) {
+          this.$__.getters = {};
+        }
+
+        if (!this.$__.getters[path]) {
+          const nested = Object.create(Document.prototype, getOwnPropertyDescriptors(this));
+
+          // save scope for nested getters/setters
+          if (!prefix) {
+            nested.$__.scope = this;
+          }
+          nested.$__.nestedPath = path;
+
+          Object.defineProperty(nested, 'schema', {
+            enumerable: false,
+            configurable: true,
+            writable: false,
+            value: prototype.schema
+          });
+
+          Object.defineProperty(nested, 'toObject', {
+            enumerable: false,
+            configurable: true,
+            writable: false,
+            value: function() {
+              return utils.clone(_this.get(path, null, {
+                virtuals: get(this, 'schema.options.toObject.virtuals', null)
+              }));
+            }
+          });
+
+          Object.defineProperty(nested, 'toJSON', {
+            enumerable: false,
+            configurable: true,
+            writable: false,
+            value: function() {
+              return _this.get(path, null, {
+                virtuals: get(_this, 'schema.options.toJSON.virtuals', null)
+              });
+            }
+          });
+
+          Object.defineProperty(nested, '$__isNested', {
+            enumerable: false,
+            configurable: true,
+            writable: false,
+            value: true
+          });
+
+          const _isEmptyOptions = Object.freeze({
+            minimize: true,
+            virtuals: false,
+            getters: false,
+            transform: false
+          });
+          Object.defineProperty(nested, '$isEmpty', {
+            enumerable: false,
+            configurable: true,
+            writable: false,
+            value: function() {
+              return Object.keys(this.get(path, null, _isEmptyOptions) || {}).length === 0;
+            }
+          });
+
+          compile(subprops, nested, path, options);
+          this.$__.getters[path] = nested;
+        }
+
+        return this.$__.getters[path];
+      },
+      set: function(v) {
+        if (v instanceof Document) {
+          v = v.toObject({ transform: false });
+        }
+        const doc = this.$__.scope || this;
+        return doc.$set(path, v);
+      }
+    });
+  } else {
+    Object.defineProperty(prototype, prop, {
+      enumerable: true,
+      configurable: true,
+      get: function() {
+        return this[getSymbol].call(this.$__.scope || this, path);
+      },
+      set: function(v) {
+        return this.$set.call(this.$__.scope || this, path, v);
+      }
+    });
+  }
+}
+
+// gets descriptors for all properties of `object`
+// makes all properties non-enumerable to match previous behavior to #2211
+function getOwnPropertyDescriptors(object) {
+  const result = {};
+
+  Object.getOwnPropertyNames(object).forEach(function(key) {
+    result[key] = Object.getOwnPropertyDescriptor(object, key);
+    // Assume these are schema paths, ignore them re: #5470
+    if (result[key].get) {
+      delete result[key];
+      return;
+    }
+    result[key].enumerable = ['isNew', '$__', 'errors', '_doc', '$locals'].indexOf(key) === -1;
+  });
+
+  return result;
+}
@@ -0,0 +1,43 @@
+'use strict';
+
+const get = require('../get');
+
+/*!
+ * Like `schema.path()`, except with a document, because impossible to
+ * determine path type without knowing the embedded discriminator key.
+ */
+
+module.exports = function getEmbeddedDiscriminatorPath(doc, path, options) {
+  options = options || {};
+  const typeOnly = options.typeOnly;
+  const parts = path.split('.');
+  let schema = null;
+  let type = 'adhocOrUndefined';
+
+  for (let i = 0; i < parts.length; ++i) {
+    const subpath = parts.slice(0, i + 1).join('.');
+    schema = doc.schema.path(subpath);
+    if (schema == null) {
+      type = 'adhocOrUndefined';
+      continue;
+    }
+    if (schema.instance === 'Mixed') {
+      return typeOnly ? 'real' : schema;
+    }
+    type = doc.schema.pathType(subpath);
+    if ((schema.$isSingleNested || schema.$isMongooseDocumentArrayElement) &&
+        schema.schema.discriminators != null) {
+      const discriminators = schema.schema.discriminators;
+      const discriminatorKey = doc.get(subpath + '.' +
+        get(schema, 'schema.options.discriminatorKey'));
+      if (discriminatorKey == null || discriminators[discriminatorKey] == null) {
+        continue;
+      }
+      const rest = parts.slice(i + 1).join('.');
+      return getEmbeddedDiscriminatorPath(doc.get(subpath), rest, options);
+    }
+  }
+
+  // Are we getting the whole schema or just the type, 'real', 'nested', etc.
+  return typeOnly ? type : schema;
+};
@@ -0,0 +1,39 @@
+'use strict';
+
+/*!
+ * Simplified lodash.get to work around the annoying null quirk. See:
+ * https://github.com/lodash/lodash/issues/3659
+ */
+
+module.exports = function get(obj, path, def) {
+  const parts = path.split('.');
+  let rest = path;
+  let cur = obj;
+  for (const part of parts) {
+    if (cur == null) {
+      return def;
+    }
+
+    // `lib/cast.js` depends on being able to get dotted paths in updates,
+    // like `{ $set: { 'a.b': 42 } }`
+    if (cur[rest] != null) {
+      return cur[rest];
+    }
+
+    cur = getProperty(cur, part);
+
+    rest = rest.substr(part.length + 1);
+  }
+
+  return cur == null ? def : cur;
+};
+
+function getProperty(obj, prop) {
+  if (obj == null) {
+    return obj;
+  }
+  if (obj instanceof Map) {
+    return obj.get(prop);
+  }
+  return obj[prop];
+}
@@ -0,0 +1,12 @@
+/*!
+ * Centralize this so we can more easily work around issues with people
+ * stubbing out `process.nextTick()` in tests using sinon:
+ * https://github.com/sinonjs/lolex#automatically-incrementing-mocked-time
+ * See gh-6074
+ */
+
+'use strict';
+
+module.exports = function immediate(cb) {
+  return process.nextTick(cb);
+};
@@ -14,6 +14,7 @@ module.exports = applyHooks;
 */

 applyHooks.middlewareFunctions = [
+  'deleteOne',
  'save',
  'validate',
  'remove',
@@ -40,12 +41,22 @@ function applyHooks(model, schema, options) {
  const objToDecorate = options.decorateDoc ? model : model.prototype;

  model.$appliedHooks = true;
-  for (let i = 0; i < schema.childSchemas.length; ++i) {
-    const childModel = schema.childSchemas[i].model;
+  for (const key of Object.keys(schema.paths)) {
+    const type = schema.paths[key];
+    let childModel = null;
+    if (type.$isSingleNested) {
+      childModel = type.caster;
+    } else if (type.$isMongooseDocumentArray) {
+      childModel = type.Constructor;
+    } else {
+      continue;
+    }
+
    if (childModel.$appliedHooks) {
      continue;
    }
-    applyHooks(childModel, schema.childSchemas[i].schema, options);
+
+    applyHooks(childModel, type.schema, options);
    if (childModel.discriminators != null) {
      const keys = Object.keys(childModel.discriminators);
      for (let j = 0; j < keys.length; ++j) {
@@ -61,7 +72,7 @@ function applyHooks(model, schema, options) {

  const middleware = schema.s.hooks.
    filter(hook => {
-      if (hook.name === 'updateOne') {
+      if (hook.name === 'updateOne' || hook.name === 'deleteOne') {
        return !!hook['document'];
      }
      if (hook.name === 'remove') {
@@ -86,6 +97,8 @@ function applyHooks(model, schema, options) {
    createWrapper('validate', objToDecorate.$__validate, null, kareemOptions);
  objToDecorate.$__remove = middleware.
    createWrapper('remove', objToDecorate.$__remove, null, kareemOptions);
+  objToDecorate.$__deleteOne = middleware.
+    createWrapper('deleteOne', objToDecorate.$__deleteOne, null, kareemOptions);
  objToDecorate.$__init = middleware.
    createWrapperSync('init', objToDecorate.$__init, null, kareemOptions);

@@ -0,0 +1,56 @@
+'use strict';
+
+const get = require('../get');
+
+/*!
+ * Register methods for this model
+ *
+ * @param {Model} model
+ * @param {Schema} schema
+ */
+
+module.exports = function applyMethods(model, schema) {
+  function apply(method, schema) {
+    Object.defineProperty(model.prototype, method, {
+      get: function() {
+        const h = {};
+        for (const k in schema.methods[method]) {
+          h[k] = schema.methods[method][k].bind(this);
+        }
+        return h;
+      },
+      configurable: true
+    });
+  }
+  for (const method of Object.keys(schema.methods)) {
+    const fn = schema.methods[method];
+    if (schema.tree.hasOwnProperty(method)) {
+      throw new Error('You have a method and a property in your schema both ' +
+        'named "' + method + '"');
+    }
+    if (schema.reserved[method] &&
+        !get(schema, `methodOptions.${method}.suppressWarning`, false)) {
+      console.warn(`mongoose: the method name "${method}" is used by mongoose ` +
+        'internally, overwriting it may cause bugs. If you\'re sure you know ' +
+        'what you\'re doing, you can suppress this error by using ' +
+        `\`schema.method('${method}', fn, { suppressWarning: true })\`.`);
+    }
+    if (typeof fn === 'function') {
+      model.prototype[method] = fn;
+    } else {
+      apply(method, schema);
+    }
+  }
+
+  // Recursively call `applyMethods()` on child schemas
+  model.$appliedMethods = true;
+  for (const key of Object.keys(schema.paths)) {
+    const type = schema.paths[key];
+    if (type.$isSingleNested && !type.caster.$appliedMethods) {
+      applyMethods(type.caster, type.schema);
+    }
+    if (type.$isMongooseDocumentArray && !type.Constructor.$appliedMethods) {
+      applyMethods(type.Constructor, type.schema);
+    }
+  }
+};
@@ -0,0 +1,61 @@
+'use strict';
+
+const utils = require('../../utils');
+
+module.exports = function applyStaticHooks(model, hooks, statics) {
+  const kareemOptions = {
+    useErrorHandlers: true,
+    numCallbackParams: 1
+  };
+
+  hooks = hooks.filter(hook => hook.model !== false);
+
+  model.$__insertMany = hooks.createWrapper('insertMany',
+    model.$__insertMany, model, kareemOptions);
+
+  for (const key of Object.keys(statics)) {
+    if (hooks.hasHooks(key)) {
+      const original = model[key];
+
+      model[key] = function() {
+        const numArgs = arguments.length;
+        const lastArg = numArgs > 0 ? arguments[numArgs - 1] : null;
+        const cb = typeof lastArg === 'function' ? lastArg : null;
+        const args = Array.prototype.slice.
+          call(arguments, 0, cb == null ? numArgs : numArgs - 1);
+        // Special case: can't use `Kareem#wrap()` because it doesn't currently
+        // support wrapped functions that return a promise.
+        return utils.promiseOrCallback(cb, callback => {
+          hooks.execPre(key, model, args, function(err) {
+            if (err != null) {
+              return callback(err);
+            }
+
+            let postCalled = 0;
+            const ret = original.apply(model, args.concat(post));
+            if (ret != null && typeof ret.then === 'function') {
+              ret.then(res => post(null, res), err => post(err));
+            }
+
+            function post(error, res) {
+              if (postCalled++ > 0) {
+                return;
+              }
+
+              if (error != null) {
+                return callback(error);
+              }
+
+              hooks.execPost(key, model, [res], function(error) {
+                if (error != null) {
+                  return callback(error);
+                }
+                callback(null, res);
+              });
+            }
+          });
+        }, model.events);
+      };
+    }
+  }
+};
@@ -0,0 +1,12 @@
+'use strict';
+
+/*!
+ * Register statics for this model
+ * @param {Model} model
+ * @param {Schema} schema
+ */
+module.exports = function applyStatics(model, schema) {
+  for (const i in schema.statics) {
+    model[i] = schema.statics[i];
+  }
+};
@@ -0,0 +1,140 @@
+'use strict';
+
+const applyTimestampsToChildren = require('../update/applyTimestampsToChildren');
+const applyTimestampsToUpdate = require('../update/applyTimestampsToUpdate');
+const cast = require('../../cast');
+const castUpdate = require('../query/castUpdate');
+const setDefaultsOnInsert = require('../setDefaultsOnInsert');
+
+/*!
+ * Given a model and a bulkWrite op, return a thunk that handles casting and
+ * validating the individual op.
+ */
+
+module.exports = function castBulkWrite(model, op, options) {
+  const now = model.base.now();
+  if (op['insertOne']) {
+    return (callback) => {
+      const doc = new model(op['insertOne']['document']);
+      if (model.schema.options.timestamps != null) {
+        doc.initializeTimestamps();
+      }
+      if (options.session != null) {
+        doc.$session(options.session);
+      }
+      op['insertOne']['document'] = doc;
+      op['insertOne']['document'].validate({ __noPromise: true }, function(error) {
+        if (error) {
+          return callback(error, null);
+        }
+        callback(null);
+      });
+    };
+  } else if (op['updateOne']) {
+    op = op['updateOne'];
+    return (callback) => {
+      try {
+        op['filter'] = cast(model.schema, op['filter']);
+        op['update'] = castUpdate(model.schema, op['update'], {
+          strict: model.schema.options.strict,
+          overwrite: false
+        });
+        if (op.setDefaultsOnInsert) {
+          setDefaultsOnInsert(op['filter'], model.schema, op['update'], {
+            setDefaultsOnInsert: true,
+            upsert: op.upsert
+          });
+        }
+        if (model.schema.$timestamps != null) {
+          const createdAt = model.schema.$timestamps.createdAt;
+          const updatedAt = model.schema.$timestamps.updatedAt;
+          applyTimestampsToUpdate(now, createdAt, updatedAt, op['update'], {});
+        }
+        applyTimestampsToChildren(now, op['update'], model.schema);
+      } catch (error) {
+        return callback(error, null);
+      }
+
+      callback(null);
+    };
+  } else if (op['updateMany']) {
+    op = op['updateMany'];
+    return (callback) => {
+      try {
+        op['filter'] = cast(model.schema, op['filter']);
+        op['update'] = castUpdate(model.schema, op['update'], {
+          strict: model.schema.options.strict,
+          overwrite: false
+        });
+        if (op.setDefaultsOnInsert) {
+          setDefaultsOnInsert(op['filter'], model.schema, op['update'], {
+            setDefaultsOnInsert: true,
+            upsert: op.upsert
+          });
+        }
+        if (model.schema.$timestamps != null) {
+          const createdAt = model.schema.$timestamps.createdAt;
+          const updatedAt = model.schema.$timestamps.updatedAt;
+          applyTimestampsToUpdate(now, createdAt, updatedAt, op['update'], {});
+        }
+        applyTimestampsToChildren(now, op['update'], model.schema);
+      } catch (error) {
+        return callback(error, null);
+      }
+
+      callback(null);
+    };
+  } else if (op['replaceOne']) {
+    return (callback) => {
+      try {
+        op['replaceOne']['filter'] = cast(model.schema,
+          op['replaceOne']['filter']);
+      } catch (error) {
+        return callback(error, null);
+      }
+
+      // set `skipId`, otherwise we get "_id field cannot be changed"
+      const doc = new model(op['replaceOne']['replacement'], null, true);
+      if (model.schema.options.timestamps != null) {
+        doc.initializeTimestamps();
+      }
+      if (options.session != null) {
+        doc.$session(options.session);
+      }
+      op['replaceOne']['replacement'] = doc;
+
+      op['replaceOne']['replacement'].validate({ __noPromise: true }, function(error) {
+        if (error) {
+          return callback(error, null);
+        }
+        callback(null);
+      });
+    };
+  } else if (op['deleteOne']) {
+    return (callback) => {
+      try {
+        op['deleteOne']['filter'] = cast(model.schema,
+          op['deleteOne']['filter']);
+      } catch (error) {
+        return callback(error, null);
+      }
+
+      callback(null);
+    };
+  } else if (op['deleteMany']) {
+    return (callback) => {
+      try {
+        op['deleteMany']['filter'] = cast(model.schema,
+          op['deleteMany']['filter']);
+      } catch (error) {
+        return callback(error, null);
+      }
+
+      callback(null);
+    };
+  } else {
+    return (callback) => {
+      callback(new Error('Invalid op passed to `bulkWrite()`'), null);
+    };
+  }
+};
@@ -82,7 +82,7 @@ module.exports = function discriminator(model, name, schema, tiedValue, applyPlu
    }

    utils.merge(schema, baseSchema, {
-      omit: { discriminators: true, $parentSchema: true },
+      omit: { discriminators: true },
      omitNested: conflictingPaths.reduce((cur, path) => {
        cur['tree.' + path] = true;
        return cur;
@@ -0,0 +1,12 @@
+'use strict';
+
+module.exports = function once(fn) {
+  let called = false;
+  return function() {
+    if (called) {
+      return;
+    }
+    called = true;
+    return fn.apply(null, arguments);
+  };
+};
@@ -0,0 +1,85 @@
+'use strict';
+
+module.exports = assignRawDocsToIdStructure;
+
+/*!
+ * Assign `vals` returned by mongo query to the `rawIds`
+ * structure returned from utils.getVals() honoring
+ * query sort order if specified by user.
+ *
+ * This can be optimized.
+ *
+ * Rules:
+ *
+ *   if the value of the path is not an array, use findOne rules, else find.
+ *   for findOne the results are assigned directly to doc path (including null results).
+ *   for find, if user specified sort order, results are assigned directly
+ *   else documents are put back in original order of array if found in results
+ *
+ * @param {Array} rawIds
+ * @param {Array} vals
+ * @param {Boolean} sort
+ * @api private
+ */
+
+function assignRawDocsToIdStructure(rawIds, resultDocs, resultOrder, options, recursed) {
+  // honor user specified sort order
+  const newOrder = [];
+  const sorting = options.sort && rawIds.length > 1;
+  let doc;
+  let sid;
+  let id;
+
+  for (let i = 0; i < rawIds.length; ++i) {
+    id = rawIds[i];
+
+    if (Array.isArray(id)) {
+      // handle [ [id0, id2], [id3] ]
+      assignRawDocsToIdStructure(id, resultDocs, resultOrder, options, true);
+      newOrder.push(id);
+      continue;
+    }
+
+    if (id === null && !sorting) {
+      // keep nulls for findOne unless sorting, which always
+      // removes them (backward compat)
+      newOrder.push(id);
+      continue;
+    }
+
+    sid = String(id);
+
+    doc = resultDocs[sid];
+    // If user wants separate copies of same doc, use this option
+    if (options.clone) {
+      doc = doc.constructor.hydrate(doc._doc);
+    }
+
+    if (recursed) {
+      if (doc) {
+        if (sorting) {
+          newOrder[resultOrder[sid]] = doc;
+        } else {
+          newOrder.push(doc);
+        }
+      } else {
+        newOrder.push(id);
+      }
+    } else {
+      // apply findOne behavior - if document in results, assign, else assign null
+      newOrder[i] = doc || null;
+    }
+  }
+
+  rawIds.length = 0;
+  if (newOrder.length) {
+    // reassign the documents based on corrected order
+
+    // forEach skips over sparse entries in arrays so we
+    // can safely use this to our advantage dealing with sorted
+    // result sets too.
+    newOrder.forEach(function(doc, i) {
+      rawIds[i] = doc;
+    });
+  }
+}
@@ -0,0 +1,215 @@
+'use strict';
+
+const assignRawDocsToIdStructure = require('./assignRawDocsToIdStructure');
+const get = require('../get');
+const getVirtual = require('./getVirtual');
+const leanPopulateMap = require('./leanPopulateMap');
+const mpath = require('mpath');
+const sift = require('sift').default;
+const utils = require('../../utils');
+
+module.exports = function assignVals(o) {
+  // Options that aren't explicitly listed in `populateOptions`
+  const userOptions = get(o, 'allOptions.options.options');
+  // `o.options` contains options explicitly listed in `populateOptions`, like
+  // `match` and `limit`.
+  const populateOptions = Object.assign({}, o.options, userOptions, {
+    justOne: o.justOne
+  });
+
+  const originalIds = [].concat(o.rawIds);
+
+  // replace the original ids in our intermediate _ids structure
+  // with the documents found by query
+  assignRawDocsToIdStructure(o.rawIds, o.rawDocs, o.rawOrder, populateOptions);
+
+  // now update the original documents being populated using the
+  // result structure that contains real documents.
+  const docs = o.docs;
+  const rawIds = o.rawIds;
+  const options = o.options;
+  const count = o.count && o.isVirtual;
+
+  function setValue(val) {
+    if (count) {
+      return val;
+    }
+    if (o.justOne === true && Array.isArray(val)) {
+      return valueFilter(val[0], options, populateOptions);
+    } else if (o.justOne === false && !Array.isArray(val)) {
+      return valueFilter([val], options, populateOptions);
+    }
+    return valueFilter(val, options, populateOptions);
+  }
+
+  for (let i = 0; i < docs.length; ++i) {
+    const existingVal = utils.getValue(o.path, docs[i]);
+    if (existingVal == null && !getVirtual(o.originalModel.schema, o.path)) {
+      continue;
+    }
+
+    let valueToSet;
+    if (count) {
+      valueToSet = numDocs(rawIds[i]);
+    } else if (Array.isArray(o.match)) {
+      valueToSet = Array.isArray(rawIds[i]) ?
+        sift(o.match[i], rawIds[i]) :
+        sift(o.match[i], [rawIds[i]])[0];
+    } else {
+      valueToSet = rawIds[i];
+    }
+
+    // If we're populating a map, the existing value will be an object, so
+    // we need to transform again
+    const originalSchema = o.originalModel.schema;
+    const isDoc = get(docs[i], '$__', null) != null;
+    let isMap = isDoc ?
+      existingVal instanceof Map :
+      utils.isPOJO(existingVal);
+    // If we pass the first check, also make sure the local field's schematype
+    // is map (re: gh-6460)
+    isMap = isMap && get(originalSchema._getSchema(o.path), '$isSchemaMap');
+    if (!o.isVirtual && isMap) {
+      const _keys = existingVal instanceof Map ?
+        Array.from(existingVal.keys()) :
+        Object.keys(existingVal);
+      valueToSet = valueToSet.reduce((cur, v, i) => {
+        cur.set(_keys[i], v);
+        return cur;
+      }, new Map());
+    }
+
+    if (o.isVirtual && isDoc) {
+      docs[i].populated(o.path, o.justOne ? originalIds[0] : originalIds, o.allOptions);
+      // If virtual populate and doc is already init-ed, need to walk through
+      // the actual doc to set rather than setting `_doc` directly
+      mpath.set(o.path, valueToSet, docs[i], setValue);
+      continue;
+    }
+
+    const parts = o.path.split('.');
+    let cur = docs[i];
+    for (let j = 0; j < parts.length - 1; ++j) {
+      if (cur[parts[j]] == null) {
+        cur[parts[j]] = {};
+      }
+      cur = cur[parts[j]];
+      // If the property in MongoDB is a primitive, we won't be able to populate
+      // the nested path, so skip it. See gh-7545
+      if (typeof cur !== 'object') {
+        return;
+      }
+    }
+    if (docs[i].$__) {
+      docs[i].populated(o.path, o.allIds[i], o.allOptions);
+    }
+
+    // If lean, need to check that each individual virtual respects
+    // `justOne`, because you may have a populated virtual with `justOne`
+    // underneath an array. See gh-6867
+    utils.setValue(o.path, valueToSet, docs[i], setValue, false);
+  }
+};
+
+function numDocs(v) {
+  if (Array.isArray(v)) {
+    return v.length;
+  }
+  return v == null ? 0 : 1;
+}
+
+/*!
+ * 1) Apply backwards compatible find/findOne behavior to sub documents
+ *
+ *    find logic:
+ *      a) filter out non-documents
+ *      b) remove _id from sub docs when user specified
+ *
+ *    findOne
+ *      a) if no doc found, set to null
+ *      b) remove _id from sub docs when user specified
+ *
+ * 2) Remove _ids when specified by users query.
+ *
+ * background:
+ * _ids are left in the query even when user excludes them so
+ * that population mapping can occur.
+ */
+
+function valueFilter(val, assignmentOpts, populateOptions) {
+  if (Array.isArray(val)) {
+    // find logic
+    const ret = [];
+    const numValues = val.length;
+    for (let i = 0; i < numValues; ++i) {
+      const subdoc = val[i];
+      if (!isPopulatedObject(subdoc) && (!populateOptions.retainNullValues || subdoc != null)) {
+        continue;
+      }
+      maybeRemoveId(subdoc, assignmentOpts);
+      ret.push(subdoc);
+      if (assignmentOpts.originalLimit &&
+          ret.length >= assignmentOpts.originalLimit) {
+        break;
+      }
+    }
+
+    // Since we don't want to have to create a new mongoosearray, make sure to
+    // modify the array in place
+    while (val.length > ret.length) {
+      Array.prototype.pop.apply(val, []);
+    }
+    for (let i = 0; i < ret.length; ++i) {
+      val[i] = ret[i];
+    }
+    return val;
+  }
+
+  // findOne
+  if (isPopulatedObject(val)) {
+    maybeRemoveId(val, assignmentOpts);
+    return val;
+  }
+
+  if (val instanceof Map) {
+    return val;
+  }
+
+  if (populateOptions.justOne === true) {
+    return (val == null ? val : null);
+  }
+  if (populateOptions.justOne === false) {
+    return [];
+  }
+  return val;
+}
+
+/*!
+ * Remove _id from `subdoc` if user specified "lean" query option
+ */
+
+function maybeRemoveId(subdoc, assignmentOpts) {
+  if (assignmentOpts.excludeId) {
+    if (typeof subdoc.setValue === 'function') {
+      delete subdoc._doc._id;
+    } else {
+      delete subdoc._id;
+    }
+  }
+}
+
+/*!
+ * Determine if `obj` is something we can set a populated path to. Can be a
+ * document, a lean document, or an array/map that contains docs.
+ */
+
+function isPopulatedObject(obj) {
+  if (obj == null) {
+    return false;
+  }
+
+  return Array.isArray(obj) ||
+    obj.$isMongooseMap ||
+    obj.$__ != null ||
+    leanPopulateMap.has(obj);
+}
@@ -0,0 +1,196 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+const Mixed = require('../../schema/mixed');
+const get = require('../get');
+const leanPopulateMap = require('./leanPopulateMap');
+const mpath = require('mpath');
+
+/*!
+ * @param {Schema} schema
+ * @param {Object} doc POJO
+ * @param {string} path
+ */
+
+module.exports = function getSchemaTypes(schema, doc, path) {
+  const pathschema = schema.path(path);
+  const topLevelDoc = doc;
+
+  if (pathschema) {
+    return pathschema;
+  }
+
+  function search(parts, schema, subdoc, nestedPath) {
+    let p = parts.length + 1;
+    let foundschema;
+    let trypath;
+
+    while (p--) {
+      trypath = parts.slice(0, p).join('.');
+      foundschema = schema.path(trypath);
+
+      if (foundschema == null) {
+        continue;
+      }
+
+      if (foundschema.caster) {
+        // array of Mixed?
+        if (foundschema.caster instanceof Mixed) {
+          return foundschema.caster;
+        }
+
+        let schemas = null;
+        if (doc != null && foundschema.schema != null && foundschema.schema.discriminators != null) {
+          const discriminators = foundschema.schema.discriminators;
+          const discriminatorKeyPath = trypath + '.' +
+            foundschema.schema.options.discriminatorKey;
+          const keys = subdoc ? mpath.get(discriminatorKeyPath, subdoc) || [] : [];
+          schemas = Object.keys(discriminators).
+            reduce(function(cur, discriminator) {
+              if (keys.indexOf(discriminator) !== -1) {
+                cur.push(discriminators[discriminator]);
+              }
+              return cur;
+            }, []);
+        }
+
+        // Now that we found the array, we need to check if there
+        // are remaining document paths to look up for casting.
+        // Also we need to handle array.$.path since schema.path
+        // doesn't work for that.
+        // If there is no foundschema.schema we are dealing with
+        // a path like array.$
+        if (p !== parts.length && foundschema.schema) {
+          let ret;
+          if (parts[p] === '$') {
+            if (p + 1 === parts.length) {
+              // comments.$
+              return foundschema;
+            }
+            // comments.$.comments.$.title
+            ret = search(
+              parts.slice(p + 1),
+              schema,
+              subdoc ? mpath.get(trypath, subdoc) : null,
+              nestedPath.concat(parts.slice(0, p))
+            );
+            if (ret) {
+              ret.$isUnderneathDocArray = ret.$isUnderneathDocArray ||
+                !foundschema.schema.$isSingleNested;
+            }
+            return ret;
+          }
+
+          if (schemas != null && schemas.length > 0) {
+            ret = [];
+            for (let i = 0; i < schemas.length; ++i) {
+              const _ret = search(
+                parts.slice(p),
+                schemas[i],
+                subdoc ? mpath.get(trypath, subdoc) : null,
+                nestedPath.concat(parts.slice(0, p))
+              );
+              if (_ret != null) {
+                _ret.$isUnderneathDocArray = _ret.$isUnderneathDocArray ||
+                  !foundschema.schema.$isSingleNested;
+                if (_ret.$isUnderneathDocArray) {
+                  ret.$isUnderneathDocArray = true;
+                }
+                ret.push(_ret);
+              }
+            }
+            return ret;
+          } else {
+            ret = search(
+              parts.slice(p),
+              foundschema.schema,
+              subdoc ? mpath.get(trypath, subdoc) : null,
+              nestedPath.concat(parts.slice(0, p))
+            );
+
+            if (ret) {
+              ret.$isUnderneathDocArray = ret.$isUnderneathDocArray ||
+                !foundschema.schema.$isSingleNested;
+            }
+
+            return ret;
+          }
+        } else if (p !== parts.length &&
+            foundschema.$isMongooseArray &&
+            foundschema.casterConstructor.$isMongooseArray) {
+          // Nested arrays. Drill down to the bottom of the nested array.
+          // Ignore discriminators.
+          let type = foundschema;
+          while (type.$isMongooseArray && !type.$isMongooseDocumentArray) {
+            type = type.casterConstructor;
+          }
+          return search(
+            parts.slice(p),
+            type.schema,
+            null,
+            nestedPath.concat(parts.slice(0, p))
+          );
+        }
+      }
+
+      const fullPath = nestedPath.concat([trypath]).join('.');
+      if (topLevelDoc.$__ && topLevelDoc.populated(fullPath) && p < parts.length) {
+        const schema = get(doc.$__.populated[fullPath], 'options.model.schema');
+        if (schema != null) {
+          const ret = search(
+            parts.slice(p),
+            schema,
+            subdoc ? mpath.get(trypath, subdoc) : null,
+            nestedPath.concat(parts.slice(0, p))
+          );
+
+          if (ret) {
+            ret.$isUnderneathDocArray = ret.$isUnderneathDocArray ||
+              !schema.$isSingleNested;
+          }
+
+          return ret;
+        }
+      }
+
+      const _val = get(topLevelDoc, trypath);
+      if (_val != null) {
+        const model = Array.isArray(_val) && _val.length > 0 ?
+          leanPopulateMap.get(_val[0]) :
+          leanPopulateMap.get(_val);
+        // Populated using lean, `leanPopulateMap` value is the foreign model
+        const schema = model != null ? model.schema : null;
+        if (schema != null) {
+          const ret = search(
+            parts.slice(p),
+            schema,
+            subdoc ? mpath.get(trypath, subdoc) : null,
+            nestedPath.concat(parts.slice(0, p))
+          );
+
+          if (ret) {
+            ret.$isUnderneathDocArray = ret.$isUnderneathDocArray ||
+              !schema.$isSingleNested;
+          }
+
+          return ret;
+        }
+      }
+
+      return foundschema;
+    }
+  }
+
+  // look for arrays
+  const parts = path.split('.');
+  for (let i = 0; i < parts.length; ++i) {
+    if (parts[i] === '$') {
+      // Re: gh-5628, because `schema.path()` doesn't take $ into account.
+      parts[i] = '0';
+    }
+  }
+  return search(parts, schema, doc, []);
+};
@@ -0,0 +1,61 @@
+'use strict';
+
+module.exports = getVirtual;
+
+/*!
+ * ignore
+ */
+
+function getVirtual(schema, name) {
+  if (schema.virtuals[name]) {
+    return schema.virtuals[name];
+  }
+  const parts = name.split('.');
+  let cur = '';
+  let nestedSchemaPath = '';
+  for (let i = 0; i < parts.length; ++i) {
+    cur += (cur.length > 0 ? '.' : '') + parts[i];
+    if (schema.virtuals[cur]) {
+      if (i === parts.length - 1) {
+        schema.virtuals[cur].$nestedSchemaPath = nestedSchemaPath;
+        return schema.virtuals[cur];
+      }
+      continue;
+    }
+
+    if (schema.nested[cur]) {
+      continue;
+    }
+
+    if (schema.paths[cur] && schema.paths[cur].schema) {
+      schema = schema.paths[cur].schema;
+      const rest = parts.slice(i + 1).join('.');
+
+      if (schema.virtuals[rest]) {
+        if (i === parts.length - 2) {
+          schema.virtuals[rest].$nestedSchemaPath =
+            [nestedSchemaPath, cur].filter(v => !!v).join('.');
+          return schema.virtuals[rest];
+        }
+        continue;
+      }
+
+      if (i + 1 < parts.length && schema.discriminators) {
+        for (const key of Object.keys(schema.discriminators)) {
+          const _virtual = getVirtual(schema.discriminators[key], rest);
+          if (_virtual != null) {
+            _virtual.$nestedSchemaPath = [nestedSchemaPath, cur].
+              filter(v => !!v).join('.');
+            return _virtual;
+          }
+        }
+      }
+
+      nestedSchemaPath += (nestedSchemaPath.length > 0 ? '.' : '') + cur;
+      cur = '';
+      continue;
+    }
+
+    return null;
+  }
+}
@@ -0,0 +1,7 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = new WeakMap();
@@ -0,0 +1,45 @@
+'use strict';
+
+module.exports = function normalizeRefPath(refPath, doc, populatedPath) {
+  if (refPath == null) {
+    return refPath;
+  }
+
+  if (typeof refPath === 'function') {
+    refPath = refPath.call(doc, doc, populatedPath);
+  }
+
+  // If populated path has numerics, the end `refPath` should too. For example,
+  // if populating `a.0.b` instead of `a.b` and `b` has `refPath = a.c`, we
+  // should return `a.0.c` for the refPath.
+  const hasNumericProp = /(\.\d+$|\.\d+\.)/g;
+
+  if (hasNumericProp.test(populatedPath)) {
+    const chunks = populatedPath.split(hasNumericProp);
+
+    if (chunks[chunks.length - 1] === '') {
+      throw new Error('Can\'t populate individual element in an array');
+    }
+
+    let _refPath = '';
+    let _remaining = refPath;
+    // 2nd, 4th, etc. will be numeric props. For example: `[ 'a', '.0.', 'b' ]`
+    for (let i = 0; i < chunks.length; i += 2) {
+      const chunk = chunks[i];
+      if (_remaining.startsWith(chunk + '.')) {
+        _refPath += _remaining.substr(0, chunk.length) + chunks[i + 1];
+        _remaining = _remaining.substr(chunk.length + 1);
+      } else if (i === chunks.length - 1) {
+        _refPath += _remaining;
+        _remaining = '';
+        break;
+      } else {
+        throw new Error('Could not normalize ref path, chunk ' + chunk + ' not in populated path');
+      }
+    }
+
+    return _refPath;
+  }
+
+  return refPath;
+};
@@ -0,0 +1,19 @@
+'use strict';
+
+const MongooseError = require('../../error/mongooseError');
+const util = require('util');
+
+module.exports = validateRef;
+
+function validateRef(ref, path) {
+  if (typeof ref === 'string') {
+    return;
+  }
+
+  if (typeof ref === 'function') {
+    return;
+  }
+
+  throw new MongooseError('Invalid ref at path "' + path + '". Got ' +
+    util.inspect(ref, { depth: 0 }));
+}
@@ -0,0 +1,8 @@
+'use strict';
+
+if (typeof jest !== 'undefined' && typeof window !== 'undefined') {
+  console.warn('Mongoose: looks like you\'re trying to test a Mongoose app ' +
+    'with Jest\'s default jsdom test environment. Please make sure you read ' +
+    'Mongoose\'s docs on configuring Jest to test Node.js apps: ' +
+    'http://mongoosejs.com/docs/jest.html');
+}
@@ -0,0 +1,18 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = function isDefiningProjection(val) {
+  if (val == null) {
+    // `undefined` or `null` become exclusive projections
+    return true;
+  }
+  if (typeof val === 'object') {
+    // Only cases where a value does **not** define whether the whole projection
+    // is inclusive or exclusive are `$meta` and `$slice`.
+    return !('$meta' in val) && !('$slice' in val);
+  }
+  return true;
+};
@@ -0,0 +1,28 @@
+'use strict';
+
+const isDefiningProjection = require('./isDefiningProjection');
+
+/*!
+ * ignore
+ */
+
+module.exports = function isExclusive(projection) {
+  const keys = Object.keys(projection);
+  let ki = keys.length;
+  let exclude = null;
+
+  if (ki === 1 && keys[0] === '_id') {
+    exclude = !!projection[keys[ki]];
+  } else {
+    while (ki--) {
+      // Does this projection explicitly define inclusion/exclusion?
+      // Explicitly avoid `$meta` and `$slice`
+      if (keys[ki] !== '_id' && isDefiningProjection(projection[keys[ki]])) {
+        exclude = !projection[keys[ki]];
+        break;
+      }
+    }
+  }
+
+  return exclude;
+};
@@ -0,0 +1,34 @@
+'use strict';
+
+const isDefiningProjection = require('./isDefiningProjection');
+
+/*!
+ * ignore
+ */
+
+module.exports = function isInclusive(projection) {
+  if (projection == null) {
+    return false;
+  }
+
+  const props = Object.keys(projection);
+  const numProps = props.length;
+  if (numProps === 0) {
+    return false;
+  }
+
+  for (let i = 0; i < numProps; ++i) {
+    const prop = props[i];
+    // Plus paths can't define the projection (see gh-7050)
+    if (prop.charAt(0) === '+') {
+      continue;
+    }
+    // If field is truthy (1, true, etc.) and not an object, then this
+    // projection must be inclusive. If object, assume its $meta, $slice, etc.
+    if (isDefiningProjection(projection[prop]) && !!projection[prop]) {
+      return true;
+    }
+  }
+
+  return false;
+};
@@ -0,0 +1,35 @@
+'use strict';
+
+const isDefiningProjection = require('./isDefiningProjection');
+
+/*!
+ * Determines if `path` is excluded by `projection`
+ *
+ * @param {Object} projection
+ * @param {string} path
+ * @return {Boolean}
+ */
+
+module.exports = function isPathExcluded(projection, path) {
+  if (path === '_id') {
+    return projection._id === 0;
+  }
+
+  const paths = Object.keys(projection);
+  let type = null;
+
+  for (const _path of paths) {
+    if (isDefiningProjection(projection[_path])) {
+      type = projection[path] === 1 ? 'inclusive' : 'exclusive';
+      break;
+    }
+  }
+
+  if (type === 'inclusive') {
+    return projection[path] !== 1;
+  }
+  if (type === 'exclusive') {
+    return projection[path] === 0;
+  }
+  return false;
+};
@@ -0,0 +1,28 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = function isPathSelectedInclusive(fields, path) {
+  const chunks = path.split('.');
+  let cur = '';
+  let j;
+  let keys;
+  let numKeys;
+  for (let i = 0; i < chunks.length; ++i) {
+    cur += cur.length ? '.' : '' + chunks[i];
+    if (fields[cur]) {
+      keys = Object.keys(fields);
+      numKeys = keys.length;
+      for (j = 0; j < numKeys; ++j) {
+        if (keys[i].indexOf(cur + '.') === 0 && keys[i].indexOf(path) !== 0) {
+          continue;
+        }
+      }
+      return true;
+    }
+  }
+
+  return false;
+};
@@ -0,0 +1,70 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = applyQueryMiddleware;
+
+/*!
+ * ignore
+ */
+
+applyQueryMiddleware.middlewareFunctions = [
+  'count',
+  'countDocuments',
+  'deleteMany',
+  'deleteOne',
+  'distinct',
+  'estimatedDocumentCount',
+  'find',
+  'findOne',
+  'findOneAndDelete',
+  'findOneAndRemove',
+  'findOneAndReplace',
+  'findOneAndUpdate',
+  'remove',
+  'replaceOne',
+  'update',
+  'updateMany',
+  'updateOne'
+];
+
+/*!
+ * Apply query middleware
+ *
+ * @param {Query} query constructor
+ * @param {Model} model
+ */
+
+function applyQueryMiddleware(Query, model) {
+  const kareemOptions = {
+    useErrorHandlers: true,
+    numCallbackParams: 1,
+    nullResultByDefault: true
+  };
+
+  const middleware = model.hooks.filter(hook => {
+    if (hook.name === 'updateOne' || hook.name === 'deleteOne') {
+      return hook.query == null || !!hook.query;
+    }
+    if (hook.name === 'remove') {
+      return !!hook.query;
+    }
+    return true;
+  });
+
+  // `update()` thunk has a different name because `_update` was already taken
+  Query.prototype._execUpdate = middleware.createWrapper('update',
+    Query.prototype._execUpdate, null, kareemOptions);
+  // `distinct()` thunk has a different name because `_distinct` was already taken
+  Query.prototype.__distinct = middleware.createWrapper('distinct',
+    Query.prototype.__distinct, null, kareemOptions);
+
+  applyQueryMiddleware.middlewareFunctions.
+    filter(v => v !== 'update' && v !== 'distinct').
+    forEach(fn => {
+      Query.prototype[`_${fn}`] = middleware.createWrapper(fn,
+        Query.prototype[`_${fn}`], null, kareemOptions);
+    });
+}
@@ -52,4 +52,4 @@ module.exports = function castFilterPath(query, schematype, val) {
  }

  return val;
-};
+};
@@ -0,0 +1,442 @@
+'use strict';
+
+const CastError = require('../../error/cast');
+const StrictModeError = require('../../error/strict');
+const ValidationError = require('../../error/validation');
+const castNumber = require('../../cast/number');
+const getEmbeddedDiscriminatorPath = require('./getEmbeddedDiscriminatorPath');
+const utils = require('../../utils');
+
+/*!
+ * Casts an update op based on the given schema
+ *
+ * @param {Schema} schema
+ * @param {Object} obj
+ * @param {Object} options
+ * @param {Boolean} [options.overwrite] defaults to false
+ * @param {Boolean|String} [options.strict] defaults to true
+ * @param {Query} context passed to setters
+ * @return {Boolean} true iff the update is non-empty
+ */
+
+module.exports = function castUpdate(schema, obj, options, context, filter) {
+  if (!obj) {
+    return undefined;
+  }
+
+  const ops = Object.keys(obj);
+  let i = ops.length;
+  const ret = {};
+  let hasKeys;
+  let val;
+  let hasDollarKey = false;
+  const overwrite = options.overwrite;
+
+  filter = filter || {};
+
+  while (i--) {
+    const op = ops[i];
+    // if overwrite is set, don't do any of the special $set stuff
+    if (op[0] !== '$' && !overwrite) {
+      // fix up $set sugar
+      if (!ret.$set) {
+        if (obj.$set) {
+          ret.$set = obj.$set;
+        } else {
+          ret.$set = {};
+        }
+      }
+      ret.$set[op] = obj[op];
+      ops.splice(i, 1);
+      if (!~ops.indexOf('$set')) ops.push('$set');
+    } else if (op === '$set') {
+      if (!ret.$set) {
+        ret[op] = obj[op];
+      }
+    } else {
+      ret[op] = obj[op];
+    }
+  }
+
+  // cast each value
+  i = ops.length;
+
+  // if we get passed {} for the update, we still need to respect that when it
+  // is an overwrite scenario
+  if (overwrite) {
+    hasKeys = true;
+  }
+
+  while (i--) {
+    const op = ops[i];
+    val = ret[op];
+    hasDollarKey = hasDollarKey || op.charAt(0) === '$';
+
+    if (val &&
+        typeof val === 'object' &&
+        !Buffer.isBuffer(val) &&
+        (!overwrite || hasDollarKey)) {
+      hasKeys |= walkUpdatePath(schema, val, op, options, context, filter);
+    } else if (overwrite && ret && typeof ret === 'object') {
+      // if we are just using overwrite, cast the query and then we will
+      // *always* return the value, even if it is an empty object. We need to
+      // set hasKeys above because we need to account for the case where the
+      // user passes {} and wants to clobber the whole document
+      // Also, _walkUpdatePath expects an operation, so give it $set since that
+      // is basically what we're doing
+      walkUpdatePath(schema, ret, '$set', options, context, filter);
+    } else {
+      const msg = 'Invalid atomic update value for ' + op + '. '
+          + 'Expected an object, received ' + typeof val;
+      throw new Error(msg);
+    }
+  }
+
+  return hasKeys && ret;
+};
+
+/*!
+ * Walk each path of obj and cast its values
+ * according to its schema.
+ *
+ * @param {Schema} schema
+ * @param {Object} obj - part of a query
+ * @param {String} op - the atomic operator ($pull, $set, etc)
+ * @param {Object} options
+ * @param {Boolean|String} [options.strict]
+ * @param {Boolean} [options.omitUndefined]
+ * @param {Query} context
+ * @param {String} pref - path prefix (internal only)
+ * @return {Bool} true if this path has keys to update
+ * @api private
+ */
+
+function walkUpdatePath(schema, obj, op, options, context, filter, pref) {
+  const strict = options.strict;
+  const prefix = pref ? pref + '.' : '';
+  const keys = Object.keys(obj);
+  let i = keys.length;
+  let hasKeys = false;
+  let schematype;
+  let key;
+  let val;
+
+  let aggregatedError = null;
+
+  let useNestedStrict;
+  if (options.useNestedStrict === undefined) {
+    useNestedStrict = schema.options.useNestedStrict;
+  } else {
+    useNestedStrict = options.useNestedStrict;
+  }
+
+  while (i--) {
+    key = keys[i];
+    val = obj[key];
+
+    if (val && val.constructor.name === 'Object') {
+      // watch for embedded doc schemas
+      schematype = schema._getSchema(prefix + key);
+      if (schematype && schematype.caster && op in castOps) {
+        // embedded doc schema
+        if ('$each' in val) {
+          hasKeys = true;
+          try {
+            obj[key] = {
+              $each: castUpdateVal(schematype, val.$each, op, key, context, prefix + key)
+            };
+          } catch (error) {
+            aggregatedError = _handleCastError(error, context, key, aggregatedError);
+          }
+
+          if (val.$slice != null) {
+            obj[key].$slice = val.$slice | 0;
+          }
+
+          if (val.$sort) {
+            obj[key].$sort = val.$sort;
+          }
+
+          if (!!val.$position || val.$position === 0) {
+            obj[key].$position = val.$position;
+          }
+        } else {
+          try {
+            obj[key] = castUpdateVal(schematype, val, op, key, context, prefix + key);
+          } catch (error) {
+            aggregatedError = _handleCastError(error, context, key, aggregatedError);
+          }
+
+          if (options.omitUndefined && obj[key] === void 0) {
+            delete obj[key];
+            continue;
+          }
+
+          hasKeys = true;
+        }
+      } else if ((op === '$currentDate') || (op in castOps && schematype)) {
+        // $currentDate can take an object
+        try {
+          obj[key] = castUpdateVal(schematype, val, op, key, context, prefix + key);
+        } catch (error) {
+          aggregatedError = _handleCastError(error, context, key, aggregatedError);
+        }
+
+        if (options.omitUndefined && obj[key] === void 0) {
+          delete obj[key];
+          continue;
+        }
+
+        hasKeys = true;
+      } else {
+        const pathToCheck = (prefix + key);
+        const v = schema._getPathType(pathToCheck);
+        let _strict = strict;
+        if (useNestedStrict &&
+            v &&
+            v.schema &&
+            'strict' in v.schema.options) {
+          _strict = v.schema.options.strict;
+        }
+
+        if (v.pathType === 'undefined') {
+          if (_strict === 'throw') {
+            throw new StrictModeError(pathToCheck);
+          } else if (_strict) {
+            delete obj[key];
+            continue;
+          }
+        }
+
+        // gh-2314
+        // we should be able to set a schema-less field
+        // to an empty object literal
+        hasKeys |= walkUpdatePath(schema, val, op, options, context, filter, prefix + key) ||
+          (utils.isObject(val) && Object.keys(val).length === 0);
+      }
+    } else {
+      const checkPath = (key === '$each' || key === '$or' || key === '$and' || key === '$in') ?
+        pref : prefix + key;
+      schematype = schema._getSchema(checkPath);
+      let pathDetails = schema._getPathType(checkPath);
+
+      // If no schema type, check for embedded discriminators
+      if (schematype == null) {
+        const _res = getEmbeddedDiscriminatorPath(schema, obj, filter, checkPath);
+        if (_res.schematype != null) {
+          schematype = _res.schematype;
+          pathDetails = _res.type;
+        }
+      }
+
+      let isStrict = strict;
+      if (useNestedStrict &&
+          pathDetails &&
+          pathDetails.schema &&
+          'strict' in pathDetails.schema.options) {
+        isStrict = pathDetails.schema.options.strict;
+      }
+
+      const skip = isStrict &&
+        !schematype &&
+        !/real|nested/.test(pathDetails.pathType);
+
+      if (skip) {
+        // Even if strict is `throw`, avoid throwing an error because of
+        // virtuals because of #6731
+        if (isStrict === 'throw' && schema.virtuals[checkPath] == null) {
+          throw new StrictModeError(prefix + key);
+        } else {
+          delete obj[key];
+        }
+      } else {
+        // gh-1845 temporary fix: ignore $rename. See gh-3027 for tracking
+        // improving this.
+        if (op === '$rename') {
+          hasKeys = true;
+          continue;
+        }
+
+        try {
+          obj[key] = castUpdateVal(schematype, val, op, key, context, prefix + key);
+        } catch (error) {
+          aggregatedError = _handleCastError(error, context, key, aggregatedError);
+        }
+
+        if (Array.isArray(obj[key]) && (op === '$addToSet' || op === '$push') && key !== '$each') {
+          if (schematype && schematype.caster && !schematype.caster.$isMongooseArray) {
+            obj[key] = { $each: obj[key] };
+          }
+        }
+
+        if (options.omitUndefined && obj[key] === void 0) {
+          delete obj[key];
+          continue;
+        }
+
+        hasKeys = true;
+      }
+    }
+  }
+
+  if (aggregatedError != null) {
+    throw aggregatedError;
+  }
+
+  return hasKeys;
+}
+
+/*!
+ * ignore
+ */
+
+function _handleCastError(error, query, key, aggregatedError) {
+  if (typeof query !== 'object' || !query.options.multipleCastError) {
+    throw error;
+  }
+  aggregatedError = aggregatedError || new ValidationError();
+  aggregatedError.addError(key, error);
+  return aggregatedError;
+}
+
+/*!
+ * These operators should be cast to numbers instead
+ * of their path schema type.
+ */
+
+const numberOps = {
+  $pop: 1,
+  $inc: 1
+};
+
+/*!
+ * These ops require no casting because the RHS doesn't do anything.
+ */
+
+const noCastOps = {
+  $unset: 1
+};
+
+/*!
+ * These operators require casting docs
+ * to real Documents for Update operations.
+ */
+
+const castOps = {
+  $push: 1,
+  $addToSet: 1,
+  $set: 1,
+  $setOnInsert: 1
+};
+
+/*!
+ * ignore
+ */
+
+const overwriteOps = {
+  $set: 1,
+  $setOnInsert: 1
+};
+
+/*!
+ * Casts `val` according to `schema` and atomic `op`.
+ *
+ * @param {SchemaType} schema
+ * @param {Object} val
+ * @param {String} op - the atomic operator ($pull, $set, etc)
+ * @param {String} $conditional
+ * @param {Query} context
+ * @api private
+ */
+
+function castUpdateVal(schema, val, op, $conditional, context, path) {
+  if (!schema) {
+    // non-existing schema path
+    if (op in numberOps) {
+      try {
+        return castNumber(val);
+      } catch (err) {
+        throw new CastError('number', val, path);
+      }
+    }
+    return val;
+  }
+
+  const cond = schema.caster && op in castOps &&
+      (utils.isObject(val) || Array.isArray(val));
+  if (cond && !overwriteOps[op]) {
+    // Cast values for ops that add data to MongoDB.
+    // Ensures embedded documents get ObjectIds etc.
+    let schemaArrayDepth = 0;
+    let cur = schema;
+    while (cur.$isMongooseArray) {
+      ++schemaArrayDepth;
+      cur = cur.caster;
+    }
+    let arrayDepth = 0;
+    let _val = val;
+    while (Array.isArray(_val)) {
+      ++arrayDepth;
+      _val = _val[0];
+    }
+
+    const additionalNesting = schemaArrayDepth - arrayDepth;
+    while (arrayDepth < schemaArrayDepth) {
+      val = [val];
+      ++arrayDepth;
+    }
+
+    let tmp = schema.cast(Array.isArray(val) ? val : [val]);
+
+    for (let i = 0; i < additionalNesting; ++i) {
+      tmp = tmp[0];
+    }
+    return tmp;
+  }
+
+  if (op in noCastOps) {
+    return val;
+  }
+  if (op in numberOps) {
+    // Null and undefined not allowed for $pop, $inc
+    if (val == null) {
+      throw new CastError('number', val, schema.path);
+    }
+    if (op === '$inc') {
+      // Support `$inc` with long, int32, etc. (gh-4283)
+      return schema.castForQueryWrapper({
+        val: val,
+        context: context
+      });
+    }
+    try {
+      return castNumber(val);
+    } catch (error) {
+      throw new CastError('number', val, schema.path);
+    }
+  }
+  if (op === '$currentDate') {
+    if (typeof val === 'object') {
+      return {$type: val.$type};
+    }
+    return Boolean(val);
+  }
+
+  if (/^\$/.test($conditional)) {
+    return schema.castForQueryWrapper({
+      $conditional: $conditional,
+      val: val,
+      context: context
+    });
+  }
+
+  if (overwriteOps[op]) {
+    return schema.castForQueryWrapper({
+      val: val,
+      context: context,
+      $skipQueryCastForUpdate: val != null && schema.$isMongooseArray && schema.$fullPath != null && !schema.$fullPath.match(/\d+$/)
+    });
+  }
+
+  return schema.castForQueryWrapper({ val: val, context: context });
+}
@@ -0,0 +1,47 @@
+'use strict';
+
+const helpers = require('../../queryhelpers');
+
+module.exports = completeMany;
+
+/*!
+ * Given a model and an array of docs, hydrates all the docs to be instances
+ * of the model. Used to initialize docs returned from the db from `find()`
+ *
+ * @param {Model} model
+ * @param {Array} docs
+ * @param {Object} fields the projection used, including `select` from schemas
+ * @param {Object} userProvidedFields the user-specified projection
+ * @param {Object} opts
+ * @param {Array} [opts.populated]
+ * @param {ClientSession} [opts.session]
+ * @param {Function} callback
+ */
+
+function completeMany(model, docs, fields, userProvidedFields, opts, callback) {
+  const arr = [];
+  let count = docs.length;
+  const len = count;
+  let error = null;
+
+  function init(_error) {
+    if (_error != null) {
+      error = error || _error;
+    }
+    if (error != null) {
+      --count || process.nextTick(() => callback(error));
+      return;
+    }
+    --count || process.nextTick(() => callback(error, arr));
+  }
+
+  for (let i = 0; i < len; ++i) {
+    arr[i] = helpers.createModel(model, docs[i], fields, userProvidedFields);
+    try {
+      arr[i].init(docs[i], opts, init);
+    } catch (error) {
+      init(error);
+    }
+    arr[i].$session(opts.session);
+  }
+}
@@ -0,0 +1,53 @@
+'use strict';
+
+const cleanPositionalOperators = require('../schema/cleanPositionalOperators');
+const get = require('../get');
+
+/*!
+ * Like `schema.path()`, except with a document, because impossible to
+ * determine path type without knowing the embedded discriminator key.
+ */
+
+module.exports = function getEmbeddedDiscriminatorPath(schema, update, filter, path) {
+  const parts = path.split('.');
+  let schematype = null;
+  let type = 'adhocOrUndefined';
+
+  filter = filter || {};
+  update = update || {};
+
+  for (let i = 0; i < parts.length; ++i) {
+    const subpath = cleanPositionalOperators(parts.slice(0, i + 1).join('.'));
+    schematype = schema.path(subpath);
+    if (schematype == null) {
+      continue;
+    }
+    type = schema.pathType(subpath);
+    if ((schematype.$isSingleNested || schematype.$isMongooseDocumentArrayElement) &&
+        schematype.schema.discriminators != null) {
+      const discriminators = schematype.schema.discriminators;
+      const discriminatorValuePath = subpath + '.' +
+        get(schematype, 'schema.options.discriminatorKey');
+      const discriminatorFilterPath =
+        discriminatorValuePath.replace(/\.\d+\./, '.');
+      let discriminatorKey = null;
+      if (discriminatorValuePath in filter) {
+        discriminatorKey = filter[discriminatorValuePath];
+      }
+      if (discriminatorFilterPath in filter) {
+        discriminatorKey = filter[discriminatorFilterPath];
+      }
+      if (discriminatorKey == null || discriminators[discriminatorKey] == null) {
+        continue;
+      }
+      const rest = parts.slice(i + 1).join('.');
+      schematype = discriminators[discriminatorKey].path(rest);
+      if (schematype != null) {
+        type = discriminators[discriminatorKey]._getPathType(rest);
+        break;
+      }
+    }
+  }
+
+  return { type: type, schematype: schematype };
+};
@@ -0,0 +1,16 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = function(obj) {
+  const keys = Object.keys(obj);
+  const len = keys.length;
+  for (let i = 0; i < len; ++i) {
+    if (keys[i].charAt(0) === '$') {
+      return true;
+    }
+  }
+  return false;
+};
@@ -0,0 +1,46 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+module.exports = function selectPopulatedFields(query) {
+  const opts = query._mongooseOptions;
+
+  if (opts.populate != null) {
+    const paths = Object.keys(opts.populate);
+    const userProvidedFields = query._userProvidedFields || {};
+    if (query.selectedInclusively()) {
+      for (let i = 0; i < paths.length; ++i) {
+        if (!isPathInFields(userProvidedFields, paths[i])) {
+          query.select(paths[i]);
+        } else if (userProvidedFields[paths[i]] === 0) {
+          delete query._fields[paths[i]];
+        }
+      }
+    } else if (query.selectedExclusively()) {
+      for (let i = 0; i < paths.length; ++i) {
+        if (userProvidedFields[paths[i]] == null) {
+          delete query._fields[paths[i]];
+        }
+      }
+    }
+  }
+};
+
+/*!
+ * ignore
+ */
+
+function isPathInFields(userProvidedFields, path) {
+  const pieces = path.split('.');
+  const len = pieces.length;
+  let cur = pieces[0];
+  for (let i = 1; i < len; ++i) {
+    if (userProvidedFields[cur] != null) {
+      return true;
+    }
+    cur += '.' + pieces[i];
+  }
+  return userProvidedFields[cur] != null;
+}
@@ -0,0 +1,18 @@
+'use strict';
+
+/*!
+ * A query thunk is the function responsible for sending the query to MongoDB,
+ * like `Query#_findOne()` or `Query#_execUpdate()`. The `Query#exec()` function
+ * calls a thunk. The term "thunk" here is the traditional Node.js definition:
+ * a function that takes exactly 1 parameter, a callback.
+ *
+ * This function defines common behavior for all query thunks.
+ */
+
+module.exports = function wrapThunk(fn) {
+  return function _wrappedThunk(cb) {
+    ++this._executionCount;
+
+    fn.call(this, cb);
+  };
+};
@@ -0,0 +1,43 @@
+'use strict';
+
+module.exports = function applyPlugins(schema, plugins, options, cacheKey) {
+  if (schema[cacheKey]) {
+    return;
+  }
+  schema[cacheKey] = true;
+
+  if (!options || !options.skipTopLevel) {
+    for (let i = 0; i < plugins.length; ++i) {
+      schema.plugin(plugins[i][0], plugins[i][1]);
+    }
+  }
+
+  options = Object.assign({}, options);
+  delete options.skipTopLevel;
+
+  for (const path of Object.keys(schema.paths)) {
+    const type = schema.paths[path];
+    if (type.schema != null) {
+      applyPlugins(type.schema, plugins, options, cacheKey);
+
+      // Recompile schema because plugins may have changed it, see gh-7572
+      type.caster.prototype.$__setSchema(type.schema);
+    }
+  }
+
+  const discriminators = schema.discriminators;
+  if (discriminators == null) {
+    return;
+  }
+
+  const applyPluginsToDiscriminators = options.applyPluginsToDiscriminators;
+
+  const keys = Object.keys(discriminators);
+  for (let i = 0; i < keys.length; ++i) {
+    const discriminatorKey = keys[i];
+    const discriminatorSchema = discriminators[discriminatorKey];
+
+    applyPlugins(discriminatorSchema, plugins,
+      { skipTopLevel: !applyPluginsToDiscriminators }, cacheKey);
+  }
+};
@@ -0,0 +1,16 @@
+'use strict';
+
+const get = require('../get');
+
+module.exports = function applyWriteConcern(schema, options) {
+  const writeConcern = get(schema, 'options.writeConcern', {});
+  if (!('w' in options) && writeConcern.w != null) {
+    options.w = writeConcern.w;
+  }
+  if (!('j' in options) && writeConcern.j != null) {
+    options.j = writeConcern.j;
+  }
+  if (!('wtimeout' in options) && writeConcern.wtimeout != null) {
+    options.wtimeout = writeConcern.wtimeout;
+  }
+};
@@ -0,0 +1,12 @@
+'use strict';
+
+/**
+ * For consistency's sake, we replace positional operator `$` and array filters
+ * `$[]` and `$[foo]` with `0` when looking up schema paths.
+ */
+
+module.exports = function cleanPositionalOperators(path) {
+  return path.
+    replace(/\.\$(\[[^\]]*\])?\./g, '.0.').
+    replace(/\.(\[[^\]]*\])?\$$/g, '.0');
+};
@@ -0,0 +1,124 @@
+'use strict';
+
+const get = require('../get');
+const utils = require('../../utils');
+
+/*!
+ * Gather all indexes defined in the schema, including single nested,
+ * document arrays, and embedded discriminators.
+ */
+
+module.exports = function getIndexes(schema) {
+  let indexes = [];
+  const schemaStack = new WeakMap();
+  const indexTypes = schema.constructor.indexTypes;
+
+  const collectIndexes = function(schema, prefix) {
+    // Ignore infinitely nested schemas, if we've already seen this schema
+    // along this path there must be a cycle
+    if (schemaStack.has(schema)) {
+      return;
+    }
+    schemaStack.set(schema, true);
+
+    prefix = prefix || '';
+    const keys = Object.keys(schema.paths);
+    const length = keys.length;
+
+    for (let i = 0; i < length; ++i) {
+      const key = keys[i];
+      const path = schema.paths[key];
+
+      if (path.$isMongooseDocumentArray || path.$isSingleNested) {
+        if (get(path, 'options.excludeIndexes') !== true &&
+            get(path, 'schemaOptions.excludeIndexes') !== true) {
+          collectIndexes(path.schema, prefix + key + '.');
+        }
+
+        if (path.schema.discriminators != null) {
+          const discriminators = path.schema.discriminators;
+          const discriminatorKeys = Object.keys(discriminators);
+          for (const discriminatorKey of discriminatorKeys) {
+            collectIndexes(discriminators[discriminatorKey]._originalSchema,
+              prefix + key + '.');
+          }
+        }
+
+        // Retained to minimize risk of backwards breaking changes due to
+        // gh-6113
+        if (path.$isMongooseDocumentArray) {
+          continue;
+        }
+      }
+
+      const index = path._index || (path.caster && path.caster._index);
+
+      if (index !== false && index !== null && index !== undefined) {
+        const field = {};
+        const isObject = utils.isObject(index);
+        const options = isObject ? index : {};
+        const type = typeof index === 'string' ? index :
+          isObject ? index.type :
+            false;
+
+        if (type && indexTypes.indexOf(type) !== -1) {
+          field[prefix + key] = type;
+        } else if (options.text) {
+          field[prefix + key] = 'text';
+          delete options.text;
+        } else {
+          field[prefix + key] = 1;
+        }
+
+        delete options.type;
+        if (!('background' in options)) {
+          options.background = true;
+        }
+
+        indexes.push([field, options]);
+      }
+    }
+
+    schemaStack.delete(schema);
+
+    if (prefix) {
+      fixSubIndexPaths(schema, prefix);
+    } else {
+      schema._indexes.forEach(function(index) {
+        if (!('background' in index[1])) {
+          index[1].background = true;
+        }
+      });
+      indexes = indexes.concat(schema._indexes);
+    }
+  };
+
+  collectIndexes(schema);
+  return indexes;
+
+  /*!
+   * Checks for indexes added to subdocs using Schema.index().
+   * These indexes need their paths prefixed properly.
+   *
+   * schema._indexes = [ [indexObj, options], [indexObj, options] ..]
+   */
+
+  function fixSubIndexPaths(schema, prefix) {
+    const subindexes = schema._indexes;
+    const len = subindexes.length;
+    for (let i = 0; i < len; ++i) {
+      const indexObj = subindexes[i][0];
+      const keys = Object.keys(indexObj);
+      const klen = keys.length;
+      const newindex = {};
+
+      // use forward iteration, order matters
+      for (let j = 0; j < klen; ++j) {
+        const key = keys[j];
+        newindex[prefix + key] = indexObj[key];
+      }
+
+      indexes.push([newindex, subindexes[i][1]]);
+    }
+  }
+};
@@ -0,0 +1,35 @@
+'use strict';
+
+/*!
+ * Behaves like `Schema#path()`, except for it also digs into arrays without
+ * needing to put `.0.`, so `getPath(schema, 'docArr.elProp')` works.
+ */
+
+module.exports = function getPath(schema, path) {
+  let schematype = schema.path(path);
+  if (schematype != null) {
+    return schematype;
+  }
+
+  const pieces = path.split('.');
+  let cur = '';
+  let isArray = false;
+
+  for (const piece of pieces) {
+    if (/^\d+$/.test(piece) && isArray) {
+      continue;
+    }
+    cur = cur.length === 0 ? piece : cur + '.' + piece;
+
+    schematype = schema.path(cur);
+    if (schematype != null && schematype.schema) {
+      schema = schematype.schema;
+      cur = '';
+      if (schematype.$isMongooseDocumentArray) {
+        isArray = true;
+      }
+    }
+  }
+
+  return schematype;
+};
@@ -0,0 +1,24 @@
+'use strict';
+
+module.exports = handleTimestampOption;
+
+/*!
+ * ignore
+ */
+
+function handleTimestampOption(arg, prop) {
+  if (arg == null) {
+    return null;
+  }
+
+  if (typeof arg === 'boolean') {
+    return prop;
+  }
+  if (typeof arg[prop] === 'boolean') {
+    return arg[prop] ? prop : null;
+  }
+  if (!(prop in arg)) {
+    return prop;
+  }
+  return arg[prop];
+}
@@ -0,0 +1,19 @@
+'use strict';
+
+module.exports = function merge(s1, s2) {
+  s1.add(s2.obj);
+
+  s1.callQueue = s1.callQueue.concat(s2.callQueue);
+  s1.method(s2.methods);
+  s1.static(s2.statics);
+
+  for (const query in s2.query) {
+    s1.query[query] = s2.query[query];
+  }
+
+  for (const virtual in s2.virtuals) {
+    s1.virtuals[virtual] = s2.virtuals[virtual].clone();
+  }
+
+  s1.s.hooks.merge(s2.s.hooks, false);
+};
@@ -0,0 +1,117 @@
+'use strict';
+
+const modifiedPaths = require('./common').modifiedPaths;
+
+/**
+ * Applies defaults to update and findOneAndUpdate operations.
+ *
+ * @param {Object} filter
+ * @param {Schema} schema
+ * @param {Object} castedDoc
+ * @param {Object} options
+ * @method setDefaultsOnInsert
+ * @api private
+ */
+
+module.exports = function(filter, schema, castedDoc, options) {
+  const keys = Object.keys(castedDoc || {});
+  const updatedKeys = {};
+  const updatedValues = {};
+  const numKeys = keys.length;
+  const modified = {};
+
+  let hasDollarUpdate = false;
+
+  options = options || {};
+
+  if (!options.upsert || !options.setDefaultsOnInsert) {
+    return castedDoc;
+  }
+
+  for (let i = 0; i < numKeys; ++i) {
+    if (keys[i].charAt(0) === '$') {
+      modifiedPaths(castedDoc[keys[i]], '', modified);
+      hasDollarUpdate = true;
+    }
+  }
+
+  if (!hasDollarUpdate) {
+    modifiedPaths(castedDoc, '', modified);
+  }
+
+  const paths = Object.keys(filter);
+  const numPaths = paths.length;
+  for (let i = 0; i < numPaths; ++i) {
+    const path = paths[i];
+    const condition = filter[path];
+    if (condition && typeof condition === 'object') {
+      const conditionKeys = Object.keys(condition);
+      const numConditionKeys = conditionKeys.length;
+      let hasDollarKey = false;
+      for (let j = 0; j < numConditionKeys; ++j) {
+        if (conditionKeys[j].charAt(0) === '$') {
+          hasDollarKey = true;
+          break;
+        }
+      }
+      if (hasDollarKey) {
+        continue;
+      }
+    }
+    updatedKeys[path] = true;
+    modified[path] = true;
+  }
+
+  if (options && options.overwrite && !hasDollarUpdate) {
+    // Defaults will be set later, since we're overwriting we'll cast
+    // the whole update to a document
+    return castedDoc;
+  }
+
+  schema.eachPath(function(path, schemaType) {
+    if (schemaType.$isSingleNested) {
+      // Only handle nested schemas 1-level deep to avoid infinite
+      // recursion re: https://github.com/mongodb-js/mongoose-autopopulate/issues/11
+      schemaType.schema.eachPath(function(_path, _schemaType) {
+        if (_path === '_id' && _schemaType.auto) {
+          // Ignore _id if auto id so we don't create subdocs
+          return;
+        }
+
+        const def = _schemaType.getDefault(null, true);
+        if (!isModified(modified, path + '.' + _path) &&
+            typeof def !== 'undefined') {
+          castedDoc = castedDoc || {};
+          castedDoc.$setOnInsert = castedDoc.$setOnInsert || {};
+          castedDoc.$setOnInsert[path + '.' + _path] = def;
+          updatedValues[path + '.' + _path] = def;
+        }
+      });
+    } else {
+      const def = schemaType.getDefault(null, true);
+      if (!isModified(modified, path) && typeof def !== 'undefined') {
+        castedDoc = castedDoc || {};
+        castedDoc.$setOnInsert = castedDoc.$setOnInsert || {};
+        castedDoc.$setOnInsert[path] = def;
+        updatedValues[path] = def;
+      }
+    }
+  });
+
+  return castedDoc;
+};
+
+function isModified(modified, path) {
+  if (modified[path]) {
+    return true;
+  }
+  const sp = path.split('.');
+  let cur = sp[0];
+  for (let i = 1; i < sp.length; ++i) {
+    if (modified[cur]) {
+      return true;
+    }
+    cur += '.' + sp[i];
+  }
+  return false;
+}
@@ -0,0 +1,12 @@
+'use strict';
+
+exports.arrayAtomicsSymbol = Symbol('mongoose#Array#_atomics');
+exports.arrayParentSymbol = Symbol('mongoose#Array#_parent');
+exports.arrayPathSymbol = Symbol('mongoose#Array#_path');
+exports.arraySchemaSymbol = Symbol('mongoose#Array#_schema');
+exports.documentArrayParent = Symbol('mongoose:documentArrayParent');
+exports.getSymbol = Symbol('mongoose#Document#get');
+exports.modelSymbol = Symbol('mongoose#Model');
+exports.objectIdSymbol = Symbol('mongoose#ObjectId');
+exports.schemaTypeSymbol = Symbol('mongoose#schemaType');
+exports.validatorErrorSymbol = Symbol('mongoose:validatorError');
@@ -0,0 +1,176 @@
+'use strict';
+
+const cleanPositionalOperators = require('../schema/cleanPositionalOperators');
+const handleTimestampOption = require('../schema/handleTimestampOption');
+
+module.exports = applyTimestampsToChildren;
+
+/*!
+ * ignore
+ */
+
+function applyTimestampsToChildren(now, update, schema) {
+  if (update == null) {
+    return;
+  }
+
+  const keys = Object.keys(update);
+  let key;
+  let createdAt;
+  let updatedAt;
+  let timestamps;
+  let path;
+
+  const hasDollarKey = keys.length && keys[0].charAt(0) === '$';
+
+  if (hasDollarKey) {
+    if (update.$push) {
+      for (key in update.$push) {
+        const $path = schema.path(key);
+        if (update.$push[key] &&
+            $path &&
+            $path.$isMongooseDocumentArray &&
+            $path.schema.options.timestamps) {
+          timestamps = $path.schema.options.timestamps;
+          createdAt = handleTimestampOption(timestamps, 'createdAt');
+          updatedAt = handleTimestampOption(timestamps, 'updatedAt');
+          if (update.$push[key].$each) {
+            update.$push[key].$each.forEach(function(subdoc) {
+              if (updatedAt != null) {
+                subdoc[updatedAt] = now;
+              }
+              if (createdAt != null) {
+                subdoc[createdAt] = now;
+              }
+            });
+          } else {
+            if (updatedAt != null) {
+              update.$push[key][updatedAt] = now;
+            }
+            if (createdAt != null) {
+              update.$push[key][createdAt] = now;
+            }
+          }
+        }
+      }
+    }
+    if (update.$set != null) {
+      const keys = Object.keys(update.$set);
+      for (key of keys) {
+        // Replace positional operator `$` and array filters `$[]` and `$[.*]`
+        const keyToSearch = cleanPositionalOperators(key);
+        path = schema.path(keyToSearch);
+        if (!path) {
+          continue;
+        }
+
+        let parentSchemaType = null;
+        const pieces = keyToSearch.split('.');
+        for (let i = pieces.length - 1; i > 0; --i) {
+          const s = schema.path(pieces.slice(0, i).join('.'));
+          if (s != null &&
+              (s.$isMongooseDocumentArray || s.$isSingleNested)) {
+            parentSchemaType = s;
+            break;
+          }
+        }
+
+        if (Array.isArray(update.$set[key]) && path.$isMongooseDocumentArray) {
+          applyTimestampsToDocumentArray(update.$set[key], path, now);
+        } else if (update.$set[key] && path.$isSingleNested) {
+          applyTimestampsToSingleNested(update.$set[key], path, now);
+        } else if (parentSchemaType != null) {
+          timestamps = parentSchemaType.schema.options.timestamps;
+          createdAt = handleTimestampOption(timestamps, 'createdAt');
+          updatedAt = handleTimestampOption(timestamps, 'updatedAt');
+
+          if (updatedAt == null) {
+            continue;
+          }
+
+          if (parentSchemaType.$isSingleNested) {
+            // Single nested is easy
+            update.$set[parentSchemaType.path + '.' + updatedAt] = now;
+            continue;
+          }
+
+          let childPath = key.substr(parentSchemaType.path.length + 1);
+
+          if (/^\d+$/.test(childPath)) {
+            update.$set[parentSchemaType.path + '.' + childPath][updatedAt] = now;
+            continue;
+          }
+
+          const firstDot = childPath.indexOf('.');
+          childPath = firstDot !== -1 ? childPath.substr(0, firstDot) : childPath;
+
+          update.$set[parentSchemaType.path + '.' + childPath + '.' + updatedAt] = now;
+        } else if (path.schema != null && path.schema != schema && update.$set[key]) {
+          timestamps = path.schema.options.timestamps;
+          createdAt = handleTimestampOption(timestamps, 'createdAt');
+          updatedAt = handleTimestampOption(timestamps, 'updatedAt');
+
+          if (updatedAt != null) {
+            update.$set[key][updatedAt] = now;
+          }
+          if (createdAt != null) {
+            update.$set[key][createdAt] = now;
+          }
+        }
+      }
+    }
+  } else {
+    const keys = Object.keys(update).filter(key => !key.startsWith('$'));
+    for (key of keys) {
+      // Replace positional operator `$` and array filters `$[]` and `$[.*]`
+      const keyToSearch = cleanPositionalOperators(key);
+      path = schema.path(keyToSearch);
+      if (!path) {
+        continue;
+      }
+
+      if (Array.isArray(update[key]) && path.$isMongooseDocumentArray) {
+        applyTimestampsToDocumentArray(update[key], path, now);
+      } else if (update[key] != null && path.$isSingleNested) {
+        applyTimestampsToSingleNested(update[key], path, now);
+      }
+    }
+  }
+}
+
+function applyTimestampsToDocumentArray(arr, schematype, now) {
+  const timestamps = schematype.schema.options.timestamps;
+
+  if (!timestamps) {
+    return;
+  }
+
+  const len = arr.length;
+
+  const createdAt = handleTimestampOption(timestamps, 'createdAt');
+  const updatedAt = handleTimestampOption(timestamps, 'updatedAt');
+  for (let i = 0; i < len; ++i) {
+    if (updatedAt != null) {
+      arr[i][updatedAt] = now;
+    }
+    if (createdAt != null) {
+      arr[i][createdAt] = now;
+    }
+  }
+}
+
+function applyTimestampsToSingleNested(subdoc, schematype, now) {
+  const timestamps = schematype.schema.options.timestamps;
+  if (!timestamps) {
+    return;
+  }
+
+  const createdAt = handleTimestampOption(timestamps, 'createdAt');
+  const updatedAt = handleTimestampOption(timestamps, 'updatedAt');
+  if (updatedAt != null) {
+    subdoc[updatedAt] = now;
+  }
+  if (createdAt != null) {
+    subdoc[createdAt] = now;
+  }
+}
@@ -0,0 +1,65 @@
+'use strict';
+
+/*!
+ * ignore
+ */
+
+const get = require('../get');
+
+module.exports = applyTimestampsToUpdate;
+
+/*!
+ * ignore
+ */
+
+function applyTimestampsToUpdate(now, createdAt, updatedAt, currentUpdate, options) {
+  const updates = currentUpdate;
+  let _updates = updates;
+  const overwrite = get(options, 'overwrite', false);
+  const timestamps = get(options, 'timestamps', true);
+
+  // Support skipping timestamps at the query level, see gh-6980
+  if (!timestamps || updates == null) {
+    return currentUpdate;
+  }
+
+  if (overwrite) {
+    if (currentUpdate && currentUpdate.$set) {
+      currentUpdate = currentUpdate.$set;
+      updates.$set = {};
+      _updates = updates.$set;
+    }
+    if (updatedAt && !currentUpdate[updatedAt]) {
+      _updates[updatedAt] = now;
+    }
+    if (createdAt && !currentUpdate[createdAt]) {
+      _updates[createdAt] = now;
+    }
+    return updates;
+  }
+  updates.$set = updates.$set || {};
+  currentUpdate = currentUpdate || {};
+
+  if (updatedAt &&
+      (!currentUpdate.$currentDate || !currentUpdate.$currentDate[updatedAt])) {
+    updates.$set[updatedAt] = now;
+  }
+
+  if (createdAt) {
+    if (currentUpdate[createdAt]) {
+      delete currentUpdate[createdAt];
+    }
+    if (currentUpdate.$set && currentUpdate.$set[createdAt]) {
+      delete currentUpdate.$set[createdAt];
+    }
+
+    updates.$setOnInsert = updates.$setOnInsert || {};
+    updates.$setOnInsert[createdAt] = now;
+  }
+
+  if (Object.keys(updates.$set).length === 0) {
+    delete updates.$set;
+  }
+
+  return updates;
+}
--- a/Show More
+++ b/Show More