[Mongoose 5.0.0](https://github.com/Automattic/mongoose/blob/master/History.md#500--2018-01-17) was released on January 17, 2018. You can find more details on [backwards breaking changes in 5.0.0 on our docs site](https://mongoosejs.com/docs/migrating_to_5.html).
Check out the [plugins search site](http://plugins.mongoosejs.io/) to see hundreds of related modules from the community. Next, learn how to write your own plugin from the [docs](http://mongoosejs.com/docs/plugins.html) or [this blog post](http://thecodebarbarian.com/2015/03/06/guide-to-mongoose-plugins).
## Contributors
Pull requests are always welcome! Please base pull requests against the `master`
branch and follow the [contributing guide](https://github.com/Automattic/mongoose/blob/master/CONTRIBUTING.md).
If your pull requests makes documentation changes, please do **not**
modify any `.html` files. The `.html` files are compiled code, so please make
your changes in `docs/*.jade`, `lib/*.js`, or `test/docs/*.js`.
View all 300+ [contributors](https://github.com/Automattic/mongoose/graphs/contributors).
## Installation
First install [node.js](http://nodejs.org/) and [mongodb](https://www.mongodb.org/downloads). Then:
```sh
$ npm install mongoose
```
## Overview
### Connecting to MongoDB
First, we need to define a connection. If your app uses only one database, you should use `mongoose.connect`. If you need to create additional connections, use `mongoose.createConnection`.
Both `connect` and `createConnection` take a `mongodb://` URI, or the parameters `host, database, port, options`.
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`.
**Note:** _If the local connection fails then try using 127.0.0.1 instead of localhost. Sometimes issues may arise when the local hostname has been changed._
**Important!** Mongoose buffers all the commands until it's connected to the database. This means that you don't have to wait until it connects to MongoDB in order to define models, run queries, etc.
### Defining a Model
Models are defined through the `Schema` interface.
```js
const Schema = mongoose.Schema;
const ObjectId = Schema.ObjectId;
const BlogPost = new Schema({
author: ObjectId,
title: String,
body: String,
date: Date
});
```
Aside from defining the structure of your documents and the types of data you're storing, a Schema handles the definition of:
* [Validators](http://mongoosejs.com/docs/validation.html) (async and sync)
The first argument is the _singular_ name of the collection your model is for. **Mongoose automatically looks for the _plural_ version of your model name.** For example, if you use
Then Mongoose will create the model for your __tickets__ collection, not your __ticket__ collection.
Once we have our model, we can then instantiate it, and save it:
```js
const instance = new MyModel();
instance.my.key = 'hello';
instance.save(function (err) {
//
});
```
Or we can find documents from the same collection
```js
MyModel.find({}, function (err, docs) {
// docs.forEach
});
```
You can also `findOne`, `findById`, `update`, etc. For more details check out [the docs](http://mongoosejs.com/docs/queries.html).
**Important!** If you opened a separate connection using `mongoose.createConnection()` but attempt to access the model through `mongoose.model('ModelName')` it will not work as expected since it is not hooked up to an active db connection. In this case access your model through the connection you created:
m.save(); // does not work b/c the default connection object was never connected
```
### Embedded Documents
In the first example snippet, we defined a key in the Schema that looks like:
```
comments: [Comment]
```
Where `Comment` is a `Schema` we created. This means that creating embedded documents is as simple as:
```js
// retrieve my model
var BlogPost = mongoose.model('BlogPost');
// create a blog post
var post = new BlogPost();
// create a comment
post.comments.push({ title: 'My comment' });
post.save(function (err) {
if (!err) console.log('Success!');
});
```
The same goes for removing them:
```js
BlogPost.findById(myId, function (err, post) {
if (!err) {
post.comments[0].remove();
post.save(function (err) {
// do something
});
}
});
```
Embedded documents enjoy all the same features as your models. Defaults, validators, middleware. Whenever an error occurs, it's bubbled to the `save()` error callback, so error handling is a snap!
### Middleware
See the [docs](http://mongoosejs.com/docs/middleware.html) page.
#### Intercepting and mutating method arguments
You can intercept method arguments via middleware.
For example, this would allow you to broadcast changes about your Documents every time someone `set`s a path in your Document to a new value:
```js
schema.pre('set', function (next, path, val, typel) {
// `this` is the current Document
this.emit('set', path, val);
// Pass control to the next pre
next();
});
```
Moreover, you can mutate the incoming `method` arguments so that subsequent middleware see different values for those arguments. To do so, just pass the new values to `next`:
```js
.pre(method, function firstPre (next, methodArg1, methodArg2) {
`type`, when used in a schema has special meaning within Mongoose. If your schema requires using `type` as a nested property you must use object notation:
```js
new Schema({
broken: { type: Boolean },
asset: {
name: String,
type: String // uh oh, it broke. asset will be interpreted as String
}
});
new Schema({
works: { type: Boolean },
asset: {
name: String,
type: { type: String } // works. asset is an object with a type property
}
});
```
### Driver Access
Mongoose is built on top of the [official MongoDB Node.js driver](https://github.com/mongodb/node-mongodb-native). Each mongoose model keeps a reference to a [native MongoDB driver collection](http://mongodb.github.io/node-mongodb-native/2.1/api/Collection.html). The collection object can be accessed using `YourModel.collection`. However, using the collection object directly bypasses all mongoose features, including hooks, validation, etc. The one
notable exception that `YourModel.collection` still buffers
commands. As such, `YourModel.collection.find()` will **not**
return a cursor.
## API Docs
Find the API docs [here](http://mongoosejs.com/docs/api.html), generated using [dox](https://github.com/tj/dox)
and [acquit](https://github.com/vkarpov15/acquit).
