änderung1

venv/lib/python3.7/site-packages/django/db/models/__init__.py

@@ -0,0 +1,48 @@
+from django.core.exceptions import ObjectDoesNotExist
+from django.db.models import signals
+from django.db.models.aggregates import *  # NOQA
+from django.db.models.aggregates import __all__ as aggregates_all
+from django.db.models.constraints import *  # NOQA
+from django.db.models.constraints import __all__ as constraints_all
+from django.db.models.deletion import (
+    CASCADE, DO_NOTHING, PROTECT, SET, SET_DEFAULT, SET_NULL, ProtectedError,
+)
+from django.db.models.expressions import (
+    Case, Exists, Expression, ExpressionList, ExpressionWrapper, F, Func,
+    OuterRef, RowRange, Subquery, Value, ValueRange, When, Window, WindowFrame,
+)
+from django.db.models.fields import *  # NOQA
+from django.db.models.fields import __all__ as fields_all
+from django.db.models.fields.files import FileField, ImageField
+from django.db.models.fields.proxy import OrderWrt
+from django.db.models.indexes import *  # NOQA
+from django.db.models.indexes import __all__ as indexes_all
+from django.db.models.lookups import Lookup, Transform
+from django.db.models.manager import Manager
+from django.db.models.query import (
+    Prefetch, Q, QuerySet, prefetch_related_objects,
+)
+from django.db.models.query_utils import FilteredRelation
+
+# Imports that would create circular imports if sorted
+from django.db.models.base import DEFERRED, Model  # isort:skip
+from django.db.models.fields.related import (  # isort:skip
+    ForeignKey, ForeignObject, OneToOneField, ManyToManyField,
+    ManyToOneRel, ManyToManyRel, OneToOneRel,
+)
+
+
+__all__ = aggregates_all + constraints_all + fields_all + indexes_all
+__all__ += [
+    'ObjectDoesNotExist', 'signals',
+    'CASCADE', 'DO_NOTHING', 'PROTECT', 'SET', 'SET_DEFAULT', 'SET_NULL',
+    'ProtectedError',
+    'Case', 'Exists', 'Expression', 'ExpressionList', 'ExpressionWrapper', 'F',
+    'Func', 'OuterRef', 'RowRange', 'Subquery', 'Value', 'ValueRange', 'When',
+    'Window', 'WindowFrame',
+    'FileField', 'ImageField', 'OrderWrt', 'Lookup', 'Transform', 'Manager',
+    'Prefetch', 'Q', 'QuerySet', 'prefetch_related_objects', 'DEFERRED', 'Model',
+    'FilteredRelation',
+    'ForeignKey', 'ForeignObject', 'OneToOneField', 'ManyToManyField',
+    'ManyToOneRel', 'ManyToManyRel', 'OneToOneRel',
+]

venv/lib/python3.7/site-packages/django/db/models/aggregates.py

@@ -0,0 +1,155 @@
+"""
+Classes to represent the definitions of aggregate functions.
+"""
+from django.core.exceptions import FieldError
+from django.db.models.expressions import Case, Func, Star, When
+from django.db.models.fields import IntegerField
+from django.db.models.functions.mixins import (
+    FixDurationInputMixin, NumericOutputFieldMixin,
+)
+
+__all__ = [
+    'Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance',
+]
+
+
+class Aggregate(Func):
+    template = '%(function)s(%(distinct)s%(expressions)s)'
+    contains_aggregate = True
+    name = None
+    filter_template = '%s FILTER (WHERE %%(filter)s)'
+    window_compatible = True
+    allow_distinct = False
+
+    def __init__(self, *expressions, distinct=False, filter=None, **extra):
+        if distinct and not self.allow_distinct:
+            raise TypeError("%s does not allow distinct." % self.__class__.__name__)
+        self.distinct = distinct
+        self.filter = filter
+        super().__init__(*expressions, **extra)
+
+    def get_source_fields(self):
+        # Don't return the filter expression since it's not a source field.
+        return [e._output_field_or_none for e in super().get_source_expressions()]
+
+    def get_source_expressions(self):
+        source_expressions = super().get_source_expressions()
+        if self.filter:
+            return source_expressions + [self.filter]
+        return source_expressions
+
+    def set_source_expressions(self, exprs):
+        self.filter = self.filter and exprs.pop()
+        return super().set_source_expressions(exprs)
+
+    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
+        # Aggregates are not allowed in UPDATE queries, so ignore for_save
+        c = super().resolve_expression(query, allow_joins, reuse, summarize)
+        c.filter = c.filter and c.filter.resolve_expression(query, allow_joins, reuse, summarize)
+        if not summarize:
+            # Call Aggregate.get_source_expressions() to avoid
+            # returning self.filter and including that in this loop.
+            expressions = super(Aggregate, c).get_source_expressions()
+            for index, expr in enumerate(expressions):
+                if expr.contains_aggregate:
+                    before_resolved = self.get_source_expressions()[index]
+                    name = before_resolved.name if hasattr(before_resolved, 'name') else repr(before_resolved)
+                    raise FieldError("Cannot compute %s('%s'): '%s' is an aggregate" % (c.name, name, name))
+        return c
+
+    @property
+    def default_alias(self):
+        expressions = self.get_source_expressions()
+        if len(expressions) == 1 and hasattr(expressions[0], 'name'):
+            return '%s__%s' % (expressions[0].name, self.name.lower())
+        raise TypeError("Complex expressions require an alias")
+
+    def get_group_by_cols(self):
+        return []
+
+    def as_sql(self, compiler, connection, **extra_context):
+        extra_context['distinct'] = 'DISTINCT ' if self.distinct else ''
+        if self.filter:
+            if connection.features.supports_aggregate_filter_clause:
+                filter_sql, filter_params = self.filter.as_sql(compiler, connection)
+                template = self.filter_template % extra_context.get('template', self.template)
+                sql, params = super().as_sql(
+                    compiler, connection, template=template, filter=filter_sql,
+                    **extra_context
+                )
+                return sql, params + filter_params
+            else:
+                copy = self.copy()
+                copy.filter = None
+                source_expressions = copy.get_source_expressions()
+                condition = When(self.filter, then=source_expressions[0])
+                copy.set_source_expressions([Case(condition)] + source_expressions[1:])
+                return super(Aggregate, copy).as_sql(compiler, connection, **extra_context)
+        return super().as_sql(compiler, connection, **extra_context)
+
+    def _get_repr_options(self):
+        options = super()._get_repr_options()
+        if self.distinct:
+            options['distinct'] = self.distinct
+        if self.filter:
+            options['filter'] = self.filter
+        return options
+
+
+class Avg(FixDurationInputMixin, NumericOutputFieldMixin, Aggregate):
+    function = 'AVG'
+    name = 'Avg'
+
+
+class Count(Aggregate):
+    function = 'COUNT'
+    name = 'Count'
+    output_field = IntegerField()
+    allow_distinct = True
+
+    def __init__(self, expression, filter=None, **extra):
+        if expression == '*':
+            expression = Star()
+        if isinstance(expression, Star) and filter is not None:
+            raise ValueError('Star cannot be used with filter. Please specify a field.')
+        super().__init__(expression, filter=filter, **extra)
+
+    def convert_value(self, value, expression, connection):
+        return 0 if value is None else value
+
+
+class Max(Aggregate):
+    function = 'MAX'
+    name = 'Max'
+
+
+class Min(Aggregate):
+    function = 'MIN'
+    name = 'Min'
+
+
+class StdDev(NumericOutputFieldMixin, Aggregate):
+    name = 'StdDev'
+
+    def __init__(self, expression, sample=False, **extra):
+        self.function = 'STDDEV_SAMP' if sample else 'STDDEV_POP'
+        super().__init__(expression, **extra)
+
+    def _get_repr_options(self):
+        return {**super()._get_repr_options(), 'sample': self.function == 'STDDEV_SAMP'}
+
+
+class Sum(FixDurationInputMixin, Aggregate):
+    function = 'SUM'
+    name = 'Sum'
+
+
+class Variance(NumericOutputFieldMixin, Aggregate):
+    name = 'Variance'
+
+    def __init__(self, expression, sample=False, **extra):
+        self.function = 'VAR_SAMP' if sample else 'VAR_POP'
+        super().__init__(expression, **extra)
+
+    def _get_repr_options(self):
+        return {**super()._get_repr_options(), 'sample': self.function == 'VAR_SAMP'}

venv/lib/python3.7/site-packages/django/db/models/deletion.py

@@ -0,0 +1,329 @@
+from collections import Counter, OrderedDict
+from operator import attrgetter
+
+from django.db import IntegrityError, connections, transaction
+from django.db.models import signals, sql
+
+
+class ProtectedError(IntegrityError):
+    def __init__(self, msg, protected_objects):
+        self.protected_objects = protected_objects
+        super().__init__(msg, protected_objects)
+
+
+def CASCADE(collector, field, sub_objs, using):
+    collector.collect(sub_objs, source=field.remote_field.model,
+                      source_attr=field.name, nullable=field.null)
+    if field.null and not connections[using].features.can_defer_constraint_checks:
+        collector.add_field_update(field, None, sub_objs)
+
+
+def PROTECT(collector, field, sub_objs, using):
+    raise ProtectedError(
+        "Cannot delete some instances of model '%s' because they are "
+        "referenced through a protected foreign key: '%s.%s'" % (
+            field.remote_field.model.__name__, sub_objs[0].__class__.__name__, field.name
+        ),
+        sub_objs
+    )
+
+
+def SET(value):
+    if callable(value):
+        def set_on_delete(collector, field, sub_objs, using):
+            collector.add_field_update(field, value(), sub_objs)
+    else:
+        def set_on_delete(collector, field, sub_objs, using):
+            collector.add_field_update(field, value, sub_objs)
+    set_on_delete.deconstruct = lambda: ('django.db.models.SET', (value,), {})
+    return set_on_delete
+
+
+def SET_NULL(collector, field, sub_objs, using):
+    collector.add_field_update(field, None, sub_objs)
+
+
+def SET_DEFAULT(collector, field, sub_objs, using):
+    collector.add_field_update(field, field.get_default(), sub_objs)
+
+
+def DO_NOTHING(collector, field, sub_objs, using):
+    pass
+
+
+def get_candidate_relations_to_delete(opts):
+    # The candidate relations are the ones that come from N-1 and 1-1 relations.
+    # N-N  (i.e., many-to-many) relations aren't candidates for deletion.
+    return (
+        f for f in opts.get_fields(include_hidden=True)
+        if f.auto_created and not f.concrete and (f.one_to_one or f.one_to_many)
+    )
+
+
+class Collector:
+    def __init__(self, using):
+        self.using = using
+        # Initially, {model: {instances}}, later values become lists.
+        self.data = OrderedDict()
+        self.field_updates = {}  # {model: {(field, value): {instances}}}
+        # fast_deletes is a list of queryset-likes that can be deleted without
+        # fetching the objects into memory.
+        self.fast_deletes = []
+
+        # Tracks deletion-order dependency for databases without transactions
+        # or ability to defer constraint checks. Only concrete model classes
+        # should be included, as the dependencies exist only between actual
+        # database tables; proxy models are represented here by their concrete
+        # parent.
+        self.dependencies = {}  # {model: {models}}
+
+    def add(self, objs, source=None, nullable=False, reverse_dependency=False):
+        """
+        Add 'objs' to the collection of objects to be deleted.  If the call is
+        the result of a cascade, 'source' should be the model that caused it,
+        and 'nullable' should be set to True if the relation can be null.
+
+        Return a list of all objects that were not already collected.
+        """
+        if not objs:
+            return []
+        new_objs = []
+        model = objs[0].__class__
+        instances = self.data.setdefault(model, set())
+        for obj in objs:
+            if obj not in instances:
+                new_objs.append(obj)
+        instances.update(new_objs)
+        # Nullable relationships can be ignored -- they are nulled out before
+        # deleting, and therefore do not affect the order in which objects have
+        # to be deleted.
+        if source is not None and not nullable:
+            if reverse_dependency:
+                source, model = model, source
+            self.dependencies.setdefault(
+                source._meta.concrete_model, set()).add(model._meta.concrete_model)
+        return new_objs
+
+    def add_field_update(self, field, value, objs):
+        """
+        Schedule a field update. 'objs' must be a homogeneous iterable
+        collection of model instances (e.g. a QuerySet).
+        """
+        if not objs:
+            return
+        model = objs[0].__class__
+        self.field_updates.setdefault(
+            model, {}).setdefault(
+            (field, value), set()).update(objs)
+
+    def can_fast_delete(self, objs, from_field=None):
+        """
+        Determine if the objects in the given queryset-like or single object
+        can be fast-deleted. This can be done if there are no cascades, no
+        parents and no signal listeners for the object class.
+
+        The 'from_field' tells where we are coming from - we need this to
+        determine if the objects are in fact to be deleted. Allow also
+        skipping parent -> child -> parent chain preventing fast delete of
+        the child.
+        """
+        if from_field and from_field.remote_field.on_delete is not CASCADE:
+            return False
+        if hasattr(objs, '_meta'):
+            model = type(objs)
+        elif hasattr(objs, 'model') and hasattr(objs, '_raw_delete'):
+            model = objs.model
+        else:
+            return False
+        if (signals.pre_delete.has_listeners(model) or
+                signals.post_delete.has_listeners(model) or
+                signals.m2m_changed.has_listeners(model)):
+            return False
+        # The use of from_field comes from the need to avoid cascade back to
+        # parent when parent delete is cascading to child.
+        opts = model._meta
+        return (
+            all(link == from_field for link in opts.concrete_model._meta.parents.values()) and
+            # Foreign keys pointing to this model.
+            all(
+                related.field.remote_field.on_delete is DO_NOTHING
+                for related in get_candidate_relations_to_delete(opts)
+            ) and (
+                # Something like generic foreign key.
+                not any(hasattr(field, 'bulk_related_objects') for field in opts.private_fields)
+            )
+        )
+
+    def get_del_batches(self, objs, field):
+        """
+        Return the objs in suitably sized batches for the used connection.
+        """
+        conn_batch_size = max(
+            connections[self.using].ops.bulk_batch_size([field.name], objs), 1)
+        if len(objs) > conn_batch_size:
+            return [objs[i:i + conn_batch_size]
+                    for i in range(0, len(objs), conn_batch_size)]
+        else:
+            return [objs]
+
+    def collect(self, objs, source=None, nullable=False, collect_related=True,
+                source_attr=None, reverse_dependency=False, keep_parents=False):
+        """
+        Add 'objs' to the collection of objects to be deleted as well as all
+        parent instances.  'objs' must be a homogeneous iterable collection of
+        model instances (e.g. a QuerySet).  If 'collect_related' is True,
+        related objects will be handled by their respective on_delete handler.
+
+        If the call is the result of a cascade, 'source' should be the model
+        that caused it and 'nullable' should be set to True, if the relation
+        can be null.
+
+        If 'reverse_dependency' is True, 'source' will be deleted before the
+        current model, rather than after. (Needed for cascading to parent
+        models, the one case in which the cascade follows the forwards
+        direction of an FK rather than the reverse direction.)
+
+        If 'keep_parents' is True, data of parent model's will be not deleted.
+        """
+        if self.can_fast_delete(objs):
+            self.fast_deletes.append(objs)
+            return
+        new_objs = self.add(objs, source, nullable,
+                            reverse_dependency=reverse_dependency)
+        if not new_objs:
+            return
+
+        model = new_objs[0].__class__
+
+        if not keep_parents:
+            # Recursively collect concrete model's parent models, but not their
+            # related objects. These will be found by meta.get_fields()
+            concrete_model = model._meta.concrete_model
+            for ptr in concrete_model._meta.parents.values():
+                if ptr:
+                    parent_objs = [getattr(obj, ptr.name) for obj in new_objs]
+                    self.collect(parent_objs, source=model,
+                                 source_attr=ptr.remote_field.related_name,
+                                 collect_related=False,
+                                 reverse_dependency=True)
+        if collect_related:
+            parents = model._meta.parents
+            for related in get_candidate_relations_to_delete(model._meta):
+                # Preserve parent reverse relationships if keep_parents=True.
+                if keep_parents and related.model in parents:
+                    continue
+                field = related.field
+                if field.remote_field.on_delete == DO_NOTHING:
+                    continue
+                batches = self.get_del_batches(new_objs, field)
+                for batch in batches:
+                    sub_objs = self.related_objects(related, batch)
+                    if self.can_fast_delete(sub_objs, from_field=field):
+                        self.fast_deletes.append(sub_objs)
+                    elif sub_objs:
+                        field.remote_field.on_delete(self, field, sub_objs, self.using)
+            for field in model._meta.private_fields:
+                if hasattr(field, 'bulk_related_objects'):
+                    # It's something like generic foreign key.
+                    sub_objs = field.bulk_related_objects(new_objs, self.using)
+                    self.collect(sub_objs, source=model, nullable=True)
+
+    def related_objects(self, related, objs):
+        """
+        Get a QuerySet of objects related to `objs` via the relation `related`.
+        """
+        return related.related_model._base_manager.using(self.using).filter(
+            **{"%s__in" % related.field.name: objs}
+        )
+
+    def instances_with_model(self):
+        for model, instances in self.data.items():
+            for obj in instances:
+                yield model, obj
+
+    def sort(self):
+        sorted_models = []
+        concrete_models = set()
+        models = list(self.data)
+        while len(sorted_models) < len(models):
+            found = False
+            for model in models:
+                if model in sorted_models:
+                    continue
+                dependencies = self.dependencies.get(model._meta.concrete_model)
+                if not (dependencies and dependencies.difference(concrete_models)):
+                    sorted_models.append(model)
+                    concrete_models.add(model._meta.concrete_model)
+                    found = True
+            if not found:
+                return
+        self.data = OrderedDict((model, self.data[model])
+                                for model in sorted_models)
+
+    def delete(self):
+        # sort instance collections
+        for model, instances in self.data.items():
+            self.data[model] = sorted(instances, key=attrgetter("pk"))
+
+        # if possible, bring the models in an order suitable for databases that
+        # don't support transactions or cannot defer constraint checks until the
+        # end of a transaction.
+        self.sort()
+        # number of objects deleted for each model label
+        deleted_counter = Counter()
+
+        # Optimize for the case with a single obj and no dependencies
+        if len(self.data) == 1 and len(instances) == 1:
+            instance = list(instances)[0]
+            if self.can_fast_delete(instance):
+                with transaction.mark_for_rollback_on_error():
+                    count = sql.DeleteQuery(model).delete_batch([instance.pk], self.using)
+                setattr(instance, model._meta.pk.attname, None)
+                return count, {model._meta.label: count}
+
+        with transaction.atomic(using=self.using, savepoint=False):
+            # send pre_delete signals
+            for model, obj in self.instances_with_model():
+                if not model._meta.auto_created:
+                    signals.pre_delete.send(
+                        sender=model, instance=obj, using=self.using
+                    )
+
+            # fast deletes
+            for qs in self.fast_deletes:
+                count = qs._raw_delete(using=self.using)
+                deleted_counter[qs.model._meta.label] += count
+
+            # update fields
+            for model, instances_for_fieldvalues in self.field_updates.items():
+                for (field, value), instances in instances_for_fieldvalues.items():
+                    query = sql.UpdateQuery(model)
+                    query.update_batch([obj.pk for obj in instances],
+                                       {field.name: value}, self.using)
+
+            # reverse instance collections
+            for instances in self.data.values():
+                instances.reverse()
+
+            # delete instances
+            for model, instances in self.data.items():
+                query = sql.DeleteQuery(model)
+                pk_list = [obj.pk for obj in instances]
+                count = query.delete_batch(pk_list, self.using)
+                deleted_counter[model._meta.label] += count
+
+                if not model._meta.auto_created:
+                    for obj in instances:
+                        signals.post_delete.send(
+                            sender=model, instance=obj, using=self.using
+                        )
+
+        # update collected instances
+        for instances_for_fieldvalues in self.field_updates.values():
+            for (field, value), instances in instances_for_fieldvalues.items():
+                for obj in instances:
+                    setattr(obj, field.attname, value)
+        for model, instances in self.data.items():
+            for instance in instances:
+                setattr(instance, model._meta.pk.attname, None)
+        return sum(deleted_counter.values()), dict(deleted_counter)

venv/lib/python3.7/site-packages/django/db/models/fields/proxy.py

@@ -0,0 +1,18 @@
+"""
+Field-like classes that aren't really fields. It's easier to use objects that
+have the same attributes as fields sometimes (avoids a lot of special casing).
+"""
+
+from django.db.models import fields
+
+
+class OrderWrt(fields.IntegerField):
+    """
+    A proxy for the _order database field that is used when
+    Meta.order_with_respect_to is specified.
+    """
+
+    def __init__(self, *args, **kwargs):
+        kwargs['name'] = '_order'
+        kwargs['editable'] = False
+        super().__init__(*args, **kwargs)

venv/lib/python3.7/site-packages/django/db/models/functions/__init__.py

@@ -0,0 +1,42 @@
+from .comparison import Cast, Coalesce, Greatest, Least, NullIf
+from .datetime import (
+    Extract, ExtractDay, ExtractHour, ExtractIsoYear, ExtractMinute,
+    ExtractMonth, ExtractQuarter, ExtractSecond, ExtractWeek, ExtractWeekDay,
+    ExtractYear, Now, Trunc, TruncDate, TruncDay, TruncHour, TruncMinute,
+    TruncMonth, TruncQuarter, TruncSecond, TruncTime, TruncWeek, TruncYear,
+)
+from .math import (
+    Abs, ACos, ASin, ATan, ATan2, Ceil, Cos, Cot, Degrees, Exp, Floor, Ln, Log,
+    Mod, Pi, Power, Radians, Round, Sin, Sqrt, Tan,
+)
+from .text import (
+    Chr, Concat, ConcatPair, Left, Length, Lower, LPad, LTrim, Ord, Repeat,
+    Replace, Reverse, Right, RPad, RTrim, StrIndex, Substr, Trim, Upper,
+)
+from .window import (
+    CumeDist, DenseRank, FirstValue, Lag, LastValue, Lead, NthValue, Ntile,
+    PercentRank, Rank, RowNumber,
+)
+
+__all__ = [
+    # comparison and conversion
+    'Cast', 'Coalesce', 'Greatest', 'Least', 'NullIf',
+    # datetime
+    'Extract', 'ExtractDay', 'ExtractHour', 'ExtractMinute', 'ExtractMonth',
+    'ExtractQuarter', 'ExtractSecond', 'ExtractWeek', 'ExtractWeekDay',
+    'ExtractIsoYear', 'ExtractYear', 'Now', 'Trunc', 'TruncDate', 'TruncDay',
+    'TruncHour', 'TruncMinute', 'TruncMonth', 'TruncQuarter', 'TruncSecond',
+    'TruncMinute', 'TruncMonth', 'TruncQuarter', 'TruncSecond', 'TruncTime',
+    'TruncWeek', 'TruncYear',
+    # math
+    'Abs', 'ACos', 'ASin', 'ATan', 'ATan2', 'Ceil', 'Cos', 'Cot', 'Degrees',
+    'Exp', 'Floor', 'Ln', 'Log', 'Mod', 'Pi', 'Power', 'Radians', 'Round',
+    'Sin', 'Sqrt', 'Tan',
+    # text
+    'Chr', 'Concat', 'ConcatPair', 'Left', 'Length', 'Lower', 'LPad', 'LTrim',
+    'Ord', 'Repeat', 'Replace', 'Reverse', 'Right', 'RPad', 'RTrim',
+    'StrIndex', 'Substr', 'Trim', 'Upper',
+    # window
+    'CumeDist', 'DenseRank', 'FirstValue', 'Lag', 'LastValue', 'Lead',
+    'NthValue', 'Ntile', 'PercentRank', 'Rank', 'RowNumber',
+]

venv/lib/python3.7/site-packages/django/db/models/functions/comparison.py

@@ -0,0 +1,112 @@
+"""Database functions that do comparisons or type conversions."""
+from django.db.models.expressions import Func, Value
+
+
+class Cast(Func):
+    """Coerce an expression to a new field type."""
+    function = 'CAST'
+    template = '%(function)s(%(expressions)s AS %(db_type)s)'
+
+    def __init__(self, expression, output_field):
+        super().__init__(expression, output_field=output_field)
+
+    def as_sql(self, compiler, connection, **extra_context):
+        extra_context['db_type'] = self.output_field.cast_db_type(connection)
+        return super().as_sql(compiler, connection, **extra_context)
+
+    def as_sqlite(self, compiler, connection, **extra_context):
+        db_type = self.output_field.db_type(connection)
+        if db_type in {'datetime', 'time'}:
+            # Use strftime as datetime/time don't keep fractional seconds.
+            template = 'strftime(%%s, %(expressions)s)'
+            sql, params = super().as_sql(compiler, connection, template=template, **extra_context)
+            format_string = '%H:%M:%f' if db_type == 'time' else '%Y-%m-%d %H:%M:%f'
+            params.insert(0, format_string)
+            return sql, params
+        elif db_type == 'date':
+            template = 'date(%(expressions)s)'
+            return super().as_sql(compiler, connection, template=template, **extra_context)
+        return self.as_sql(compiler, connection, **extra_context)
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        # MySQL doesn't support explicit cast to float.
+        template = '(%(expressions)s + 0.0)' if self.output_field.get_internal_type() == 'FloatField' else None
+        return self.as_sql(compiler, connection, template=template, **extra_context)
+
+    def as_postgresql(self, compiler, connection, **extra_context):
+        # CAST would be valid too, but the :: shortcut syntax is more readable.
+        # 'expressions' is wrapped in parentheses in case it's a complex
+        # expression.
+        return self.as_sql(compiler, connection, template='(%(expressions)s)::%(db_type)s', **extra_context)
+
+
+class Coalesce(Func):
+    """Return, from left to right, the first non-null expression."""
+    function = 'COALESCE'
+
+    def __init__(self, *expressions, **extra):
+        if len(expressions) < 2:
+            raise ValueError('Coalesce must take at least two expressions')
+        super().__init__(*expressions, **extra)
+
+    def as_oracle(self, compiler, connection, **extra_context):
+        # Oracle prohibits mixing TextField (NCLOB) and CharField (NVARCHAR2),
+        # so convert all fields to NCLOB when that type is expected.
+        if self.output_field.get_internal_type() == 'TextField':
+            clone = self.copy()
+            clone.set_source_expressions([
+                Func(expression, function='TO_NCLOB') for expression in self.get_source_expressions()
+            ])
+            return super(Coalesce, clone).as_sql(compiler, connection, **extra_context)
+        return self.as_sql(compiler, connection, **extra_context)
+
+
+class Greatest(Func):
+    """
+    Return the maximum expression.
+
+    If any expression is null the return value is database-specific:
+    On PostgreSQL, the maximum not-null expression is returned.
+    On MySQL, Oracle, and SQLite, if any expression is null, null is returned.
+    """
+    function = 'GREATEST'
+
+    def __init__(self, *expressions, **extra):
+        if len(expressions) < 2:
+            raise ValueError('Greatest must take at least two expressions')
+        super().__init__(*expressions, **extra)
+
+    def as_sqlite(self, compiler, connection, **extra_context):
+        """Use the MAX function on SQLite."""
+        return super().as_sqlite(compiler, connection, function='MAX', **extra_context)
+
+
+class Least(Func):
+    """
+    Return the minimum expression.
+
+    If any expression is null the return value is database-specific:
+    On PostgreSQL, return the minimum not-null expression.
+    On MySQL, Oracle, and SQLite, if any expression is null, return null.
+    """
+    function = 'LEAST'
+
+    def __init__(self, *expressions, **extra):
+        if len(expressions) < 2:
+            raise ValueError('Least must take at least two expressions')
+        super().__init__(*expressions, **extra)
+
+    def as_sqlite(self, compiler, connection, **extra_context):
+        """Use the MIN function on SQLite."""
+        return super().as_sqlite(compiler, connection, function='MIN', **extra_context)
+
+
+class NullIf(Func):
+    function = 'NULLIF'
+    arity = 2
+
+    def as_oracle(self, compiler, connection, **extra_context):
+        expression1 = self.get_source_expressions()[0]
+        if isinstance(expression1, Value) and expression1.value is None:
+            raise ValueError('Oracle does not allow Value(None) for expression1.')
+        return super().as_sql(compiler, connection, **extra_context)

venv/lib/python3.7/site-packages/django/db/models/functions/datetime.py

@@ -0,0 +1,308 @@
+from datetime import datetime
+
+from django.conf import settings
+from django.db.models.expressions import Func
+from django.db.models.fields import (
+    DateField, DateTimeField, DurationField, Field, IntegerField, TimeField,
+)
+from django.db.models.lookups import (
+    Transform, YearExact, YearGt, YearGte, YearLt, YearLte,
+)
+from django.utils import timezone
+
+
+class TimezoneMixin:
+    tzinfo = None
+
+    def get_tzname(self):
+        # Timezone conversions must happen to the input datetime *before*
+        # applying a function. 2015-12-31 23:00:00 -02:00 is stored in the
+        # database as 2016-01-01 01:00:00 +00:00. Any results should be
+        # based on the input datetime not the stored datetime.
+        tzname = None
+        if settings.USE_TZ:
+            if self.tzinfo is None:
+                tzname = timezone.get_current_timezone_name()
+            else:
+                tzname = timezone._get_timezone_name(self.tzinfo)
+        return tzname
+
+
+class Extract(TimezoneMixin, Transform):
+    lookup_name = None
+    output_field = IntegerField()
+
+    def __init__(self, expression, lookup_name=None, tzinfo=None, **extra):
+        if self.lookup_name is None:
+            self.lookup_name = lookup_name
+        if self.lookup_name is None:
+            raise ValueError('lookup_name must be provided')
+        self.tzinfo = tzinfo
+        super().__init__(expression, **extra)
+
+    def as_sql(self, compiler, connection):
+        sql, params = compiler.compile(self.lhs)
+        lhs_output_field = self.lhs.output_field
+        if isinstance(lhs_output_field, DateTimeField):
+            tzname = self.get_tzname()
+            sql = connection.ops.datetime_extract_sql(self.lookup_name, sql, tzname)
+        elif isinstance(lhs_output_field, DateField):
+            sql = connection.ops.date_extract_sql(self.lookup_name, sql)
+        elif isinstance(lhs_output_field, TimeField):
+            sql = connection.ops.time_extract_sql(self.lookup_name, sql)
+        elif isinstance(lhs_output_field, DurationField):
+            if not connection.features.has_native_duration_field:
+                raise ValueError('Extract requires native DurationField database support.')
+            sql = connection.ops.time_extract_sql(self.lookup_name, sql)
+        else:
+            # resolve_expression has already validated the output_field so this
+            # assert should never be hit.
+            assert False, "Tried to Extract from an invalid type."
+        return sql, params
+
+    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
+        copy = super().resolve_expression(query, allow_joins, reuse, summarize, for_save)
+        field = copy.lhs.output_field
+        if not isinstance(field, (DateField, DateTimeField, TimeField, DurationField)):
+            raise ValueError(
+                'Extract input expression must be DateField, DateTimeField, '
+                'TimeField, or DurationField.'
+            )
+        # Passing dates to functions expecting datetimes is most likely a mistake.
+        if type(field) == DateField and copy.lookup_name in ('hour', 'minute', 'second'):
+            raise ValueError(
+                "Cannot extract time component '%s' from DateField '%s'. " % (copy.lookup_name, field.name)
+            )
+        return copy
+
+
+class ExtractYear(Extract):
+    lookup_name = 'year'
+
+
+class ExtractIsoYear(Extract):
+    """Return the ISO-8601 week-numbering year."""
+    lookup_name = 'iso_year'
+
+
+class ExtractMonth(Extract):
+    lookup_name = 'month'
+
+
+class ExtractDay(Extract):
+    lookup_name = 'day'
+
+
+class ExtractWeek(Extract):
+    """
+    Return 1-52 or 53, based on ISO-8601, i.e., Monday is the first of the
+    week.
+    """
+    lookup_name = 'week'
+
+
+class ExtractWeekDay(Extract):
+    """
+    Return Sunday=1 through Saturday=7.
+
+    To replicate this in Python: (mydatetime.isoweekday() % 7) + 1
+    """
+    lookup_name = 'week_day'
+
+
+class ExtractQuarter(Extract):
+    lookup_name = 'quarter'
+
+
+class ExtractHour(Extract):
+    lookup_name = 'hour'
+
+
+class ExtractMinute(Extract):
+    lookup_name = 'minute'
+
+
+class ExtractSecond(Extract):
+    lookup_name = 'second'
+
+
+DateField.register_lookup(ExtractYear)
+DateField.register_lookup(ExtractMonth)
+DateField.register_lookup(ExtractDay)
+DateField.register_lookup(ExtractWeekDay)
+DateField.register_lookup(ExtractWeek)
+DateField.register_lookup(ExtractIsoYear)
+DateField.register_lookup(ExtractQuarter)
+
+TimeField.register_lookup(ExtractHour)
+TimeField.register_lookup(ExtractMinute)
+TimeField.register_lookup(ExtractSecond)
+
+DateTimeField.register_lookup(ExtractHour)
+DateTimeField.register_lookup(ExtractMinute)
+DateTimeField.register_lookup(ExtractSecond)
+
+ExtractYear.register_lookup(YearExact)
+ExtractYear.register_lookup(YearGt)
+ExtractYear.register_lookup(YearGte)
+ExtractYear.register_lookup(YearLt)
+ExtractYear.register_lookup(YearLte)
+
+ExtractIsoYear.register_lookup(YearExact)
+ExtractIsoYear.register_lookup(YearGt)
+ExtractIsoYear.register_lookup(YearGte)
+ExtractIsoYear.register_lookup(YearLt)
+ExtractIsoYear.register_lookup(YearLte)
+
+
+class Now(Func):
+    template = 'CURRENT_TIMESTAMP'
+    output_field = DateTimeField()
+
+    def as_postgresql(self, compiler, connection, **extra_context):
+        # PostgreSQL's CURRENT_TIMESTAMP means "the time at the start of the
+        # transaction". Use STATEMENT_TIMESTAMP to be cross-compatible with
+        # other databases.
+        return self.as_sql(compiler, connection, template='STATEMENT_TIMESTAMP()', **extra_context)
+
+
+class TruncBase(TimezoneMixin, Transform):
+    kind = None
+    tzinfo = None
+
+    def __init__(self, expression, output_field=None, tzinfo=None, **extra):
+        self.tzinfo = tzinfo
+        super().__init__(expression, output_field=output_field, **extra)
+
+    def as_sql(self, compiler, connection):
+        inner_sql, inner_params = compiler.compile(self.lhs)
+        if isinstance(self.output_field, DateTimeField):
+            tzname = self.get_tzname()
+            sql = connection.ops.datetime_trunc_sql(self.kind, inner_sql, tzname)
+        elif isinstance(self.output_field, DateField):
+            sql = connection.ops.date_trunc_sql(self.kind, inner_sql)
+        elif isinstance(self.output_field, TimeField):
+            sql = connection.ops.time_trunc_sql(self.kind, inner_sql)
+        else:
+            raise ValueError('Trunc only valid on DateField, TimeField, or DateTimeField.')
+        return sql, inner_params
+
+    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
+        copy = super().resolve_expression(query, allow_joins, reuse, summarize, for_save)
+        field = copy.lhs.output_field
+        # DateTimeField is a subclass of DateField so this works for both.
+        assert isinstance(field, (DateField, TimeField)), (
+            "%r isn't a DateField, TimeField, or DateTimeField." % field.name
+        )
+        # If self.output_field was None, then accessing the field will trigger
+        # the resolver to assign it to self.lhs.output_field.
+        if not isinstance(copy.output_field, (DateField, DateTimeField, TimeField)):
+            raise ValueError('output_field must be either DateField, TimeField, or DateTimeField')
+        # Passing dates or times to functions expecting datetimes is most
+        # likely a mistake.
+        class_output_field = self.__class__.output_field if isinstance(self.__class__.output_field, Field) else None
+        output_field = class_output_field or copy.output_field
+        has_explicit_output_field = class_output_field or field.__class__ is not copy.output_field.__class__
+        if type(field) == DateField and (
+                isinstance(output_field, DateTimeField) or copy.kind in ('hour', 'minute', 'second', 'time')):
+            raise ValueError("Cannot truncate DateField '%s' to %s. " % (
+                field.name, output_field.__class__.__name__ if has_explicit_output_field else 'DateTimeField'
+            ))
+        elif isinstance(field, TimeField) and (
+                isinstance(output_field, DateTimeField) or
+                copy.kind in ('year', 'quarter', 'month', 'week', 'day', 'date')):
+            raise ValueError("Cannot truncate TimeField '%s' to %s. " % (
+                field.name, output_field.__class__.__name__ if has_explicit_output_field else 'DateTimeField'
+            ))
+        return copy
+
+    def convert_value(self, value, expression, connection):
+        if isinstance(self.output_field, DateTimeField):
+            if not settings.USE_TZ:
+                pass
+            elif value is not None:
+                value = value.replace(tzinfo=None)
+                value = timezone.make_aware(value, self.tzinfo)
+            elif not connection.features.has_zoneinfo_database:
+                raise ValueError(
+                    'Database returned an invalid datetime value. Are time '
+                    'zone definitions for your database installed?'
+                )
+        elif isinstance(value, datetime):
+            if value is None:
+                pass
+            elif isinstance(self.output_field, DateField):
+                value = value.date()
+            elif isinstance(self.output_field, TimeField):
+                value = value.time()
+        return value
+
+
+class Trunc(TruncBase):
+
+    def __init__(self, expression, kind, output_field=None, tzinfo=None, **extra):
+        self.kind = kind
+        super().__init__(expression, output_field=output_field, tzinfo=tzinfo, **extra)
+
+
+class TruncYear(TruncBase):
+    kind = 'year'
+
+
+class TruncQuarter(TruncBase):
+    kind = 'quarter'
+
+
+class TruncMonth(TruncBase):
+    kind = 'month'
+
+
+class TruncWeek(TruncBase):
+    """Truncate to midnight on the Monday of the week."""
+    kind = 'week'
+
+
+class TruncDay(TruncBase):
+    kind = 'day'
+
+
+class TruncDate(TruncBase):
+    kind = 'date'
+    lookup_name = 'date'
+    output_field = DateField()
+
+    def as_sql(self, compiler, connection):
+        # Cast to date rather than truncate to date.
+        lhs, lhs_params = compiler.compile(self.lhs)
+        tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
+        sql = connection.ops.datetime_cast_date_sql(lhs, tzname)
+        return sql, lhs_params
+
+
+class TruncTime(TruncBase):
+    kind = 'time'
+    lookup_name = 'time'
+    output_field = TimeField()
+
+    def as_sql(self, compiler, connection):
+        # Cast to time rather than truncate to time.
+        lhs, lhs_params = compiler.compile(self.lhs)
+        tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
+        sql = connection.ops.datetime_cast_time_sql(lhs, tzname)
+        return sql, lhs_params
+
+
+class TruncHour(TruncBase):
+    kind = 'hour'
+
+
+class TruncMinute(TruncBase):
+    kind = 'minute'
+
+
+class TruncSecond(TruncBase):
+    kind = 'second'
+
+
+DateTimeField.register_lookup(TruncDate)
+DateTimeField.register_lookup(TruncTime)

venv/lib/python3.7/site-packages/django/db/models/indexes.py

@@ -0,0 +1,131 @@
+from django.db.backends.utils import names_digest, split_identifier
+from django.db.models.query_utils import Q
+from django.db.models.sql import Query
+
+__all__ = ['Index']
+
+
+class Index:
+    suffix = 'idx'
+    # The max length of the name of the index (restricted to 30 for
+    # cross-database compatibility with Oracle)
+    max_name_length = 30
+
+    def __init__(self, *, fields=(), name=None, db_tablespace=None, opclasses=(), condition=None):
+        if opclasses and not name:
+            raise ValueError('An index must be named to use opclasses.')
+        if not isinstance(condition, (type(None), Q)):
+            raise ValueError('Index.condition must be a Q instance.')
+        if condition and not name:
+            raise ValueError('An index must be named to use condition.')
+        if not isinstance(fields, (list, tuple)):
+            raise ValueError('Index.fields must be a list or tuple.')
+        if not isinstance(opclasses, (list, tuple)):
+            raise ValueError('Index.opclasses must be a list or tuple.')
+        if opclasses and len(fields) != len(opclasses):
+            raise ValueError('Index.fields and Index.opclasses must have the same number of elements.')
+        if not fields:
+            raise ValueError('At least one field is required to define an index.')
+        self.fields = list(fields)
+        # A list of 2-tuple with the field name and ordering ('' or 'DESC').
+        self.fields_orders = [
+            (field_name[1:], 'DESC') if field_name.startswith('-') else (field_name, '')
+            for field_name in self.fields
+        ]
+        self.name = name or ''
+        if self.name:
+            errors = self.check_name()
+            if len(self.name) > self.max_name_length:
+                errors.append('Index names cannot be longer than %s characters.' % self.max_name_length)
+            if errors:
+                raise ValueError(errors)
+        self.db_tablespace = db_tablespace
+        self.opclasses = opclasses
+        self.condition = condition
+
+    def check_name(self):
+        errors = []
+        # Name can't start with an underscore on Oracle; prepend D if needed.
+        if self.name[0] == '_':
+            errors.append('Index names cannot start with an underscore (_).')
+            self.name = 'D%s' % self.name[1:]
+        # Name can't start with a number on Oracle; prepend D if needed.
+        elif self.name[0].isdigit():
+            errors.append('Index names cannot start with a number (0-9).')
+            self.name = 'D%s' % self.name[1:]
+        return errors
+
+    def _get_condition_sql(self, model, schema_editor):
+        if self.condition is None:
+            return None
+        query = Query(model=model)
+        where = query.build_where(self.condition)
+        compiler = query.get_compiler(connection=schema_editor.connection)
+        sql, params = where.as_sql(compiler, schema_editor.connection)
+        return sql % tuple(schema_editor.quote_value(p) for p in params)
+
+    def create_sql(self, model, schema_editor, using=''):
+        fields = [model._meta.get_field(field_name) for field_name, _ in self.fields_orders]
+        col_suffixes = [order[1] for order in self.fields_orders]
+        condition = self._get_condition_sql(model, schema_editor)
+        return schema_editor._create_index_sql(
+            model, fields, name=self.name, using=using, db_tablespace=self.db_tablespace,
+            col_suffixes=col_suffixes, opclasses=self.opclasses, condition=condition,
+        )
+
+    def remove_sql(self, model, schema_editor):
+        return schema_editor._delete_index_sql(model, self.name)
+
+    def deconstruct(self):
+        path = '%s.%s' % (self.__class__.__module__, self.__class__.__name__)
+        path = path.replace('django.db.models.indexes', 'django.db.models')
+        kwargs = {'fields': self.fields, 'name': self.name}
+        if self.db_tablespace is not None:
+            kwargs['db_tablespace'] = self.db_tablespace
+        if self.opclasses:
+            kwargs['opclasses'] = self.opclasses
+        if self.condition:
+            kwargs['condition'] = self.condition
+        return (path, (), kwargs)
+
+    def clone(self):
+        """Create a copy of this Index."""
+        _, _, kwargs = self.deconstruct()
+        return self.__class__(**kwargs)
+
+    def set_name_with_model(self, model):
+        """
+        Generate a unique name for the index.
+
+        The name is divided into 3 parts - table name (12 chars), field name
+        (8 chars) and unique hash + suffix (10 chars). Each part is made to
+        fit its size by truncating the excess length.
+        """
+        _, table_name = split_identifier(model._meta.db_table)
+        column_names = [model._meta.get_field(field_name).column for field_name, order in self.fields_orders]
+        column_names_with_order = [
+            (('-%s' if order else '%s') % column_name)
+            for column_name, (field_name, order) in zip(column_names, self.fields_orders)
+        ]
+        # The length of the parts of the name is based on the default max
+        # length of 30 characters.
+        hash_data = [table_name] + column_names_with_order + [self.suffix]
+        self.name = '%s_%s_%s' % (
+            table_name[:11],
+            column_names[0][:7],
+            '%s_%s' % (names_digest(*hash_data, length=6), self.suffix),
+        )
+        assert len(self.name) <= self.max_name_length, (
+            'Index too long for multiple database support. Is self.suffix '
+            'longer than 3 characters?'
+        )
+        self.check_name()
+
+    def __repr__(self):
+        return "<%s: fields='%s'%s>" % (
+            self.__class__.__name__, ', '.join(self.fields),
+            '' if self.condition is None else ', condition=%s' % self.condition,
+        )
+
+    def __eq__(self, other):
+        return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())

venv/lib/python3.7/site-packages/django/db/models/manager.py

@@ -0,0 +1,201 @@
+import copy
+import inspect
+from importlib import import_module
+
+from django.db import router
+from django.db.models.query import QuerySet
+
+
+class BaseManager:
+    # To retain order, track each time a Manager instance is created.
+    creation_counter = 0
+
+    # Set to True for the 'objects' managers that are automatically created.
+    auto_created = False
+
+    #: If set to True the manager will be serialized into migrations and will
+    #: thus be available in e.g. RunPython operations.
+    use_in_migrations = False
+
+    def __new__(cls, *args, **kwargs):
+        # Capture the arguments to make returning them trivial.
+        obj = super().__new__(cls)
+        obj._constructor_args = (args, kwargs)
+        return obj
+
+    def __init__(self):
+        super().__init__()
+        self._set_creation_counter()
+        self.model = None
+        self.name = None
+        self._db = None
+        self._hints = {}
+
+    def __str__(self):
+        """Return "app_label.model_label.manager_name"."""
+        return '%s.%s' % (self.model._meta.label, self.name)
+
+    def deconstruct(self):
+        """
+        Return a 5-tuple of the form (as_manager (True), manager_class,
+        queryset_class, args, kwargs).
+
+        Raise a ValueError if the manager is dynamically generated.
+        """
+        qs_class = self._queryset_class
+        if getattr(self, '_built_with_as_manager', False):
+            # using MyQuerySet.as_manager()
+            return (
+                True,  # as_manager
+                None,  # manager_class
+                '%s.%s' % (qs_class.__module__, qs_class.__name__),  # qs_class
+                None,  # args
+                None,  # kwargs
+            )
+        else:
+            module_name = self.__module__
+            name = self.__class__.__name__
+            # Make sure it's actually there and not an inner class
+            module = import_module(module_name)
+            if not hasattr(module, name):
+                raise ValueError(
+                    "Could not find manager %s in %s.\n"
+                    "Please note that you need to inherit from managers you "
+                    "dynamically generated with 'from_queryset()'."
+                    % (name, module_name)
+                )
+            return (
+                False,  # as_manager
+                '%s.%s' % (module_name, name),  # manager_class
+                None,  # qs_class
+                self._constructor_args[0],  # args
+                self._constructor_args[1],  # kwargs
+            )
+
+    def check(self, **kwargs):
+        return []
+
+    @classmethod
+    def _get_queryset_methods(cls, queryset_class):
+        def create_method(name, method):
+            def manager_method(self, *args, **kwargs):
+                return getattr(self.get_queryset(), name)(*args, **kwargs)
+            manager_method.__name__ = method.__name__
+            manager_method.__doc__ = method.__doc__
+            return manager_method
+
+        new_methods = {}
+        for name, method in inspect.getmembers(queryset_class, predicate=inspect.isfunction):
+            # Only copy missing methods.
+            if hasattr(cls, name):
+                continue
+            # Only copy public methods or methods with the attribute `queryset_only=False`.
+            queryset_only = getattr(method, 'queryset_only', None)
+            if queryset_only or (queryset_only is None and name.startswith('_')):
+                continue
+            # Copy the method onto the manager.
+            new_methods[name] = create_method(name, method)
+        return new_methods
+
+    @classmethod
+    def from_queryset(cls, queryset_class, class_name=None):
+        if class_name is None:
+            class_name = '%sFrom%s' % (cls.__name__, queryset_class.__name__)
+        return type(class_name, (cls,), {
+            '_queryset_class': queryset_class,
+            **cls._get_queryset_methods(queryset_class),
+        })
+
+    def contribute_to_class(self, model, name):
+        self.name = self.name or name
+        self.model = model
+
+        setattr(model, name, ManagerDescriptor(self))
+
+        model._meta.add_manager(self)
+
+    def _set_creation_counter(self):
+        """
+        Set the creation counter value for this instance and increment the
+        class-level copy.
+        """
+        self.creation_counter = BaseManager.creation_counter
+        BaseManager.creation_counter += 1
+
+    def db_manager(self, using=None, hints=None):
+        obj = copy.copy(self)
+        obj._db = using or self._db
+        obj._hints = hints or self._hints
+        return obj
+
+    @property
+    def db(self):
+        return self._db or router.db_for_read(self.model, **self._hints)
+
+    #######################
+    # PROXIES TO QUERYSET #
+    #######################
+
+    def get_queryset(self):
+        """
+        Return a new QuerySet object. Subclasses can override this method to
+        customize the behavior of the Manager.
+        """
+        return self._queryset_class(model=self.model, using=self._db, hints=self._hints)
+
+    def all(self):
+        # We can't proxy this method through the `QuerySet` like we do for the
+        # rest of the `QuerySet` methods. This is because `QuerySet.all()`
+        # works by creating a "copy" of the current queryset and in making said
+        # copy, all the cached `prefetch_related` lookups are lost. See the
+        # implementation of `RelatedManager.get_queryset()` for a better
+        # understanding of how this comes into play.
+        return self.get_queryset()
+
+    def __eq__(self, other):
+        return (
+            isinstance(other, self.__class__) and
+            self._constructor_args == other._constructor_args
+        )
+
+    def __hash__(self):
+        return id(self)
+
+
+class Manager(BaseManager.from_queryset(QuerySet)):
+    pass
+
+
+class ManagerDescriptor:
+
+    def __init__(self, manager):
+        self.manager = manager
+
+    def __get__(self, instance, cls=None):
+        if instance is not None:
+            raise AttributeError("Manager isn't accessible via %s instances" % cls.__name__)
+
+        if cls._meta.abstract:
+            raise AttributeError("Manager isn't available; %s is abstract" % (
+                cls._meta.object_name,
+            ))
+
+        if cls._meta.swapped:
+            raise AttributeError(
+                "Manager isn't available; '%s.%s' has been swapped for '%s'" % (
+                    cls._meta.app_label,
+                    cls._meta.object_name,
+                    cls._meta.swapped,
+                )
+            )
+
+        return cls._meta.managers_map[self.manager.name]
+
+
+class EmptyManager(Manager):
+    def __init__(self, model):
+        super().__init__()
+        self.model = model
+
+    def get_queryset(self):
+        return super().get_queryset().none()

venv/lib/python3.7/site-packages/django/db/models/options.py

@@ -0,0 +1,828 @@
+import copy
+import inspect
+from bisect import bisect
+from collections import OrderedDict, defaultdict
+
+from django.apps import apps
+from django.conf import settings
+from django.core.exceptions import FieldDoesNotExist, ImproperlyConfigured
+from django.db import connections
+from django.db.models import Manager
+from django.db.models.fields import AutoField
+from django.db.models.fields.proxy import OrderWrt
+from django.db.models.query_utils import PathInfo
+from django.utils.datastructures import ImmutableList, OrderedSet
+from django.utils.functional import cached_property
+from django.utils.text import camel_case_to_spaces, format_lazy
+from django.utils.translation import override
+
+PROXY_PARENTS = object()
+
+EMPTY_RELATION_TREE = ()
+
+IMMUTABLE_WARNING = (
+    "The return type of '%s' should never be mutated. If you want to manipulate this list "
+    "for your own use, make a copy first."
+)
+
+DEFAULT_NAMES = (
+    'verbose_name', 'verbose_name_plural', 'db_table', 'ordering',
+    'unique_together', 'permissions', 'get_latest_by', 'order_with_respect_to',
+    'app_label', 'db_tablespace', 'abstract', 'managed', 'proxy', 'swappable',
+    'auto_created', 'index_together', 'apps', 'default_permissions',
+    'select_on_save', 'default_related_name', 'required_db_features',
+    'required_db_vendor', 'base_manager_name', 'default_manager_name',
+    'indexes', 'constraints',
+    # For backwards compatibility with Django 1.11. RemovedInDjango30Warning
+    'manager_inheritance_from_future',
+)
+
+
+def normalize_together(option_together):
+    """
+    option_together can be either a tuple of tuples, or a single
+    tuple of two strings. Normalize it to a tuple of tuples, so that
+    calling code can uniformly expect that.
+    """
+    try:
+        if not option_together:
+            return ()
+        if not isinstance(option_together, (tuple, list)):
+            raise TypeError
+        first_element = option_together[0]
+        if not isinstance(first_element, (tuple, list)):
+            option_together = (option_together,)
+        # Normalize everything to tuples
+        return tuple(tuple(ot) for ot in option_together)
+    except TypeError:
+        # If the value of option_together isn't valid, return it
+        # verbatim; this will be picked up by the check framework later.
+        return option_together
+
+
+def make_immutable_fields_list(name, data):
+    return ImmutableList(data, warning=IMMUTABLE_WARNING % name)
+
+
+class Options:
+    FORWARD_PROPERTIES = {
+        'fields', 'many_to_many', 'concrete_fields', 'local_concrete_fields',
+        '_forward_fields_map', 'managers', 'managers_map', 'base_manager',
+        'default_manager',
+    }
+    REVERSE_PROPERTIES = {'related_objects', 'fields_map', '_relation_tree'}
+
+    default_apps = apps
+
+    def __init__(self, meta, app_label=None):
+        self._get_fields_cache = {}
+        self.local_fields = []
+        self.local_many_to_many = []
+        self.private_fields = []
+        self.local_managers = []
+        self.base_manager_name = None
+        self.default_manager_name = None
+        self.model_name = None
+        self.verbose_name = None
+        self.verbose_name_plural = None
+        self.db_table = ''
+        self.ordering = []
+        self._ordering_clash = False
+        self.indexes = []
+        self.constraints = []
+        self.unique_together = []
+        self.index_together = []
+        self.select_on_save = False
+        self.default_permissions = ('add', 'change', 'delete', 'view')
+        self.permissions = []
+        self.object_name = None
+        self.app_label = app_label
+        self.get_latest_by = None
+        self.order_with_respect_to = None
+        self.db_tablespace = settings.DEFAULT_TABLESPACE
+        self.required_db_features = []
+        self.required_db_vendor = None
+        self.meta = meta
+        self.pk = None
+        self.auto_field = None
+        self.abstract = False
+        self.managed = True
+        self.proxy = False
+        # For any class that is a proxy (including automatically created
+        # classes for deferred object loading), proxy_for_model tells us
+        # which class this model is proxying. Note that proxy_for_model
+        # can create a chain of proxy models. For non-proxy models, the
+        # variable is always None.
+        self.proxy_for_model = None
+        # For any non-abstract class, the concrete class is the model
+        # in the end of the proxy_for_model chain. In particular, for
+        # concrete models, the concrete_model is always the class itself.
+        self.concrete_model = None
+        self.swappable = None
+        self.parents = OrderedDict()
+        self.auto_created = False
+
+        # List of all lookups defined in ForeignKey 'limit_choices_to' options
+        # from *other* models. Needed for some admin checks. Internal use only.
+        self.related_fkey_lookups = []
+
+        # A custom app registry to use, if you're making a separate model set.
+        self.apps = self.default_apps
+
+        self.default_related_name = None
+
+    @property
+    def label(self):
+        return '%s.%s' % (self.app_label, self.object_name)
+
+    @property
+    def label_lower(self):
+        return '%s.%s' % (self.app_label, self.model_name)
+
+    @property
+    def app_config(self):
+        # Don't go through get_app_config to avoid triggering imports.
+        return self.apps.app_configs.get(self.app_label)
+
+    @property
+    def installed(self):
+        return self.app_config is not None
+
+    def contribute_to_class(self, cls, name):
+        from django.db import connection
+        from django.db.backends.utils import truncate_name
+
+        cls._meta = self
+        self.model = cls
+        # First, construct the default values for these options.
+        self.object_name = cls.__name__
+        self.model_name = self.object_name.lower()
+        self.verbose_name = camel_case_to_spaces(self.object_name)
+
+        # Store the original user-defined values for each option,
+        # for use when serializing the model definition
+        self.original_attrs = {}
+
+        # Next, apply any overridden values from 'class Meta'.
+        if self.meta:
+            meta_attrs = self.meta.__dict__.copy()
+            for name in self.meta.__dict__:
+                # Ignore any private attributes that Django doesn't care about.
+                # NOTE: We can't modify a dictionary's contents while looping
+                # over it, so we loop over the *original* dictionary instead.
+                if name.startswith('_'):
+                    del meta_attrs[name]
+            for attr_name in DEFAULT_NAMES:
+                if attr_name in meta_attrs:
+                    setattr(self, attr_name, meta_attrs.pop(attr_name))
+                    self.original_attrs[attr_name] = getattr(self, attr_name)
+                elif hasattr(self.meta, attr_name):
+                    setattr(self, attr_name, getattr(self.meta, attr_name))
+                    self.original_attrs[attr_name] = getattr(self, attr_name)
+
+            self.unique_together = normalize_together(self.unique_together)
+            self.index_together = normalize_together(self.index_together)
+
+            # verbose_name_plural is a special case because it uses a 's'
+            # by default.
+            if self.verbose_name_plural is None:
+                self.verbose_name_plural = format_lazy('{}s', self.verbose_name)
+
+            # order_with_respect_and ordering are mutually exclusive.
+            self._ordering_clash = bool(self.ordering and self.order_with_respect_to)
+
+            # Any leftover attributes must be invalid.
+            if meta_attrs != {}:
+                raise TypeError("'class Meta' got invalid attribute(s): %s" % ','.join(meta_attrs))
+        else:
+            self.verbose_name_plural = format_lazy('{}s', self.verbose_name)
+        del self.meta
+
+        # If the db_table wasn't provided, use the app_label + model_name.
+        if not self.db_table:
+            self.db_table = "%s_%s" % (self.app_label, self.model_name)
+            self.db_table = truncate_name(self.db_table, connection.ops.max_name_length())
+
+    def _prepare(self, model):
+        if self.order_with_respect_to:
+            # The app registry will not be ready at this point, so we cannot
+            # use get_field().
+            query = self.order_with_respect_to
+            try:
+                self.order_with_respect_to = next(
+                    f for f in self._get_fields(reverse=False)
+                    if f.name == query or f.attname == query
+                )
+            except StopIteration:
+                raise FieldDoesNotExist("%s has no field named '%s'" % (self.object_name, query))
+
+            self.ordering = ('_order',)
+            if not any(isinstance(field, OrderWrt) for field in model._meta.local_fields):
+                model.add_to_class('_order', OrderWrt())
+        else:
+            self.order_with_respect_to = None
+
+        if self.pk is None:
+            if self.parents:
+                # Promote the first parent link in lieu of adding yet another
+                # field.
+                field = next(iter(self.parents.values()))
+                # Look for a local field with the same name as the
+                # first parent link. If a local field has already been
+                # created, use it instead of promoting the parent
+                already_created = [fld for fld in self.local_fields if fld.name == field.name]
+                if already_created:
+                    field = already_created[0]
+                field.primary_key = True
+                self.setup_pk(field)
+                if not field.remote_field.parent_link:
+                    raise ImproperlyConfigured(
+                        'Add parent_link=True to %s.' % field,
+                    )
+            else:
+                auto = AutoField(verbose_name='ID', primary_key=True, auto_created=True)
+                model.add_to_class('id', auto)
+
+    def add_manager(self, manager):
+        self.local_managers.append(manager)
+        self._expire_cache()
+
+    def add_field(self, field, private=False):
+        # Insert the given field in the order in which it was created, using
+        # the "creation_counter" attribute of the field.
+        # Move many-to-many related fields from self.fields into
+        # self.many_to_many.
+        if private:
+            self.private_fields.append(field)
+        elif field.is_relation and field.many_to_many:
+            self.local_many_to_many.insert(bisect(self.local_many_to_many, field), field)
+        else:
+            self.local_fields.insert(bisect(self.local_fields, field), field)
+            self.setup_pk(field)
+
+        # If the field being added is a relation to another known field,
+        # expire the cache on this field and the forward cache on the field
+        # being referenced, because there will be new relationships in the
+        # cache. Otherwise, expire the cache of references *to* this field.
+        # The mechanism for getting at the related model is slightly odd -
+        # ideally, we'd just ask for field.related_model. However, related_model
+        # is a cached property, and all the models haven't been loaded yet, so
+        # we need to make sure we don't cache a string reference.
+        if field.is_relation and hasattr(field.remote_field, 'model') and field.remote_field.model:
+            try:
+                field.remote_field.model._meta._expire_cache(forward=False)
+            except AttributeError:
+                pass
+            self._expire_cache()
+        else:
+            self._expire_cache(reverse=False)
+
+    def setup_pk(self, field):
+        if not self.pk and field.primary_key:
+            self.pk = field
+            field.serialize = False
+
+    def setup_proxy(self, target):
+        """
+        Do the internal setup so that the current model is a proxy for
+        "target".
+        """
+        self.pk = target._meta.pk
+        self.proxy_for_model = target
+        self.db_table = target._meta.db_table
+
+    def __repr__(self):
+        return '<Options for %s>' % self.object_name
+
+    def __str__(self):
+        return "%s.%s" % (self.app_label, self.model_name)
+
+    def can_migrate(self, connection):
+        """
+        Return True if the model can/should be migrated on the `connection`.
+        `connection` can be either a real connection or a connection alias.
+        """
+        if self.proxy or self.swapped or not self.managed:
+            return False
+        if isinstance(connection, str):
+            connection = connections[connection]
+        if self.required_db_vendor:
+            return self.required_db_vendor == connection.vendor
+        if self.required_db_features:
+            return all(getattr(connection.features, feat, False)
+                       for feat in self.required_db_features)
+        return True
+
+    @property
+    def verbose_name_raw(self):
+        """Return the untranslated verbose name."""
+        with override(None):
+            return str(self.verbose_name)
+
+    @property
+    def swapped(self):
+        """
+        Has this model been swapped out for another? If so, return the model
+        name of the replacement; otherwise, return None.
+
+        For historical reasons, model name lookups using get_model() are
+        case insensitive, so we make sure we are case insensitive here.
+        """
+        if self.swappable:
+            swapped_for = getattr(settings, self.swappable, None)
+            if swapped_for:
+                try:
+                    swapped_label, swapped_object = swapped_for.split('.')
+                except ValueError:
+                    # setting not in the format app_label.model_name
+                    # raising ImproperlyConfigured here causes problems with
+                    # test cleanup code - instead it is raised in get_user_model
+                    # or as part of validation.
+                    return swapped_for
+
+                if '%s.%s' % (swapped_label, swapped_object.lower()) != self.label_lower:
+                    return swapped_for
+        return None
+
+    @cached_property
+    def managers(self):
+        managers = []
+        seen_managers = set()
+        bases = (b for b in self.model.mro() if hasattr(b, '_meta'))
+        for depth, base in enumerate(bases):
+            for manager in base._meta.local_managers:
+                if manager.name in seen_managers:
+                    continue
+
+                manager = copy.copy(manager)
+                manager.model = self.model
+                seen_managers.add(manager.name)
+                managers.append((depth, manager.creation_counter, manager))
+
+        return make_immutable_fields_list(
+            "managers",
+            (m[2] for m in sorted(managers)),
+        )
+
+    @cached_property
+    def managers_map(self):
+        return {manager.name: manager for manager in self.managers}
+
+    @cached_property
+    def base_manager(self):
+        base_manager_name = self.base_manager_name
+        if not base_manager_name:
+            # Get the first parent's base_manager_name if there's one.
+            for parent in self.model.mro()[1:]:
+                if hasattr(parent, '_meta'):
+                    if parent._base_manager.name != '_base_manager':
+                        base_manager_name = parent._base_manager.name
+                    break
+
+        if base_manager_name:
+            try:
+                return self.managers_map[base_manager_name]
+            except KeyError:
+                raise ValueError(
+                    "%s has no manager named %r" % (
+                        self.object_name,
+                        base_manager_name,
+                    )
+                )
+
+        manager = Manager()
+        manager.name = '_base_manager'
+        manager.model = self.model
+        manager.auto_created = True
+        return manager
+
+    @cached_property
+    def default_manager(self):
+        default_manager_name = self.default_manager_name
+        if not default_manager_name and not self.local_managers:
+            # Get the first parent's default_manager_name if there's one.
+            for parent in self.model.mro()[1:]:
+                if hasattr(parent, '_meta'):
+                    default_manager_name = parent._meta.default_manager_name
+                    break
+
+        if default_manager_name:
+            try:
+                return self.managers_map[default_manager_name]
+            except KeyError:
+                raise ValueError(
+                    "%s has no manager named %r" % (
+                        self.object_name,
+                        default_manager_name,
+                    )
+                )
+
+        if self.managers:
+            return self.managers[0]
+
+    @cached_property
+    def fields(self):
+        """
+        Return a list of all forward fields on the model and its parents,
+        excluding ManyToManyFields.
+
+        Private API intended only to be used by Django itself; get_fields()
+        combined with filtering of field properties is the public API for
+        obtaining this field list.
+        """
+        # For legacy reasons, the fields property should only contain forward
+        # fields that are not private or with a m2m cardinality. Therefore we
+        # pass these three filters as filters to the generator.
+        # The third lambda is a longwinded way of checking f.related_model - we don't
+        # use that property directly because related_model is a cached property,
+        # and all the models may not have been loaded yet; we don't want to cache
+        # the string reference to the related_model.
+        def is_not_an_m2m_field(f):
+            return not (f.is_relation and f.many_to_many)
+
+        def is_not_a_generic_relation(f):
+            return not (f.is_relation and f.one_to_many)
+
+        def is_not_a_generic_foreign_key(f):
+            return not (
+                f.is_relation and f.many_to_one and not (hasattr(f.remote_field, 'model') and f.remote_field.model)
+            )
+
+        return make_immutable_fields_list(
+            "fields",
+            (f for f in self._get_fields(reverse=False)
+             if is_not_an_m2m_field(f) and is_not_a_generic_relation(f) and is_not_a_generic_foreign_key(f))
+        )
+
+    @cached_property
+    def concrete_fields(self):
+        """
+        Return a list of all concrete fields on the model and its parents.
+
+        Private API intended only to be used by Django itself; get_fields()
+        combined with filtering of field properties is the public API for
+        obtaining this field list.
+        """
+        return make_immutable_fields_list(
+            "concrete_fields", (f for f in self.fields if f.concrete)
+        )
+
+    @cached_property
+    def local_concrete_fields(self):
+        """
+        Return a list of all concrete fields on the model.
+
+        Private API intended only to be used by Django itself; get_fields()
+        combined with filtering of field properties is the public API for
+        obtaining this field list.
+        """
+        return make_immutable_fields_list(
+            "local_concrete_fields", (f for f in self.local_fields if f.concrete)
+        )
+
+    @cached_property
+    def many_to_many(self):
+        """
+        Return a list of all many to many fields on the model and its parents.
+
+        Private API intended only to be used by Django itself; get_fields()
+        combined with filtering of field properties is the public API for
+        obtaining this list.
+        """
+        return make_immutable_fields_list(
+            "many_to_many",
+            (f for f in self._get_fields(reverse=False) if f.is_relation and f.many_to_many)
+        )
+
+    @cached_property
+    def related_objects(self):
+        """
+        Return all related objects pointing to the current model. The related
+        objects can come from a one-to-one, one-to-many, or many-to-many field
+        relation type.
+
+        Private API intended only to be used by Django itself; get_fields()
+        combined with filtering of field properties is the public API for
+        obtaining this field list.
+        """
+        all_related_fields = self._get_fields(forward=False, reverse=True, include_hidden=True)
+        return make_immutable_fields_list(
+            "related_objects",
+            (obj for obj in all_related_fields if not obj.hidden or obj.field.many_to_many)
+        )
+
+    @cached_property
+    def _forward_fields_map(self):
+        res = {}
+        fields = self._get_fields(reverse=False)
+        for field in fields:
+            res[field.name] = field
+            # Due to the way Django's internals work, get_field() should also
+            # be able to fetch a field by attname. In the case of a concrete
+            # field with relation, includes the *_id name too
+            try:
+                res[field.attname] = field
+            except AttributeError:
+                pass
+        return res
+
+    @cached_property
+    def fields_map(self):
+        res = {}
+        fields = self._get_fields(forward=False, include_hidden=True)
+        for field in fields:
+            res[field.name] = field
+            # Due to the way Django's internals work, get_field() should also
+            # be able to fetch a field by attname. In the case of a concrete
+            # field with relation, includes the *_id name too
+            try:
+                res[field.attname] = field
+            except AttributeError:
+                pass
+        return res
+
+    def get_field(self, field_name):
+        """
+        Return a field instance given the name of a forward or reverse field.
+        """
+        try:
+            # In order to avoid premature loading of the relation tree
+            # (expensive) we prefer checking if the field is a forward field.
+            return self._forward_fields_map[field_name]
+        except KeyError:
+            # If the app registry is not ready, reverse fields are
+            # unavailable, therefore we throw a FieldDoesNotExist exception.
+            if not self.apps.models_ready:
+                raise FieldDoesNotExist(
+                    "%s has no field named '%s'. The app cache isn't ready yet, "
+                    "so if this is an auto-created related field, it won't "
+                    "be available yet." % (self.object_name, field_name)
+                )
+
+        try:
+            # Retrieve field instance by name from cached or just-computed
+            # field map.
+            return self.fields_map[field_name]
+        except KeyError:
+            raise FieldDoesNotExist("%s has no field named '%s'" % (self.object_name, field_name))
+
+    def get_base_chain(self, model):
+        """
+        Return a list of parent classes leading to `model` (ordered from
+        closest to most distant ancestor). This has to handle the case where
+        `model` is a grandparent or even more distant relation.
+        """
+        if not self.parents:
+            return []
+        if model in self.parents:
+            return [model]
+        for parent in self.parents:
+            res = parent._meta.get_base_chain(model)
+            if res:
+                res.insert(0, parent)
+                return res
+        return []
+
+    def get_parent_list(self):
+        """
+        Return all the ancestors of this model as a list ordered by MRO.
+        Useful for determining if something is an ancestor, regardless of lineage.
+        """
+        result = OrderedSet(self.parents)
+        for parent in self.parents:
+            for ancestor in parent._meta.get_parent_list():
+                result.add(ancestor)
+        return list(result)
+
+    def get_ancestor_link(self, ancestor):
+        """
+        Return the field on the current model which points to the given
+        "ancestor". This is possible an indirect link (a pointer to a parent
+        model, which points, eventually, to the ancestor). Used when
+        constructing table joins for model inheritance.
+
+        Return None if the model isn't an ancestor of this one.
+        """
+        if ancestor in self.parents:
+            return self.parents[ancestor]
+        for parent in self.parents:
+            # Tries to get a link field from the immediate parent
+            parent_link = parent._meta.get_ancestor_link(ancestor)
+            if parent_link:
+                # In case of a proxied model, the first link
+                # of the chain to the ancestor is that parent
+                # links
+                return self.parents[parent] or parent_link
+
+    def get_path_to_parent(self, parent):
+        """
+        Return a list of PathInfos containing the path from the current
+        model to the parent model, or an empty list if parent is not a
+        parent of the current model.
+        """
+        if self.model is parent:
+            return []
+        # Skip the chain of proxy to the concrete proxied model.
+        proxied_model = self.concrete_model
+        path = []
+        opts = self
+        for int_model in self.get_base_chain(parent):
+            if int_model is proxied_model:
+                opts = int_model._meta
+            else:
+                final_field = opts.parents[int_model]
+                targets = (final_field.remote_field.get_related_field(),)
+                opts = int_model._meta
+                path.append(PathInfo(
+                    from_opts=final_field.model._meta,
+                    to_opts=opts,
+                    target_fields=targets,
+                    join_field=final_field,
+                    m2m=False,
+                    direct=True,
+                    filtered_relation=None,
+                ))
+        return path
+
+    def get_path_from_parent(self, parent):
+        """
+        Return a list of PathInfos containing the path from the parent
+        model to the current model, or an empty list if parent is not a
+        parent of the current model.
+        """
+        if self.model is parent:
+            return []
+        model = self.concrete_model
+        # Get a reversed base chain including both the current and parent
+        # models.
+        chain = model._meta.get_base_chain(parent)
+        chain.reverse()
+        chain.append(model)
+        # Construct a list of the PathInfos between models in chain.
+        path = []
+        for i, ancestor in enumerate(chain[:-1]):
+            child = chain[i + 1]
+            link = child._meta.get_ancestor_link(ancestor)
+            path.extend(link.get_reverse_path_info())
+        return path
+
+    def _populate_directed_relation_graph(self):
+        """
+        This method is used by each model to find its reverse objects. As this
+        method is very expensive and is accessed frequently (it looks up every
+        field in a model, in every app), it is computed on first access and then
+        is set as a property on every model.
+        """
+        related_objects_graph = defaultdict(list)
+
+        all_models = self.apps.get_models(include_auto_created=True)
+        for model in all_models:
+            opts = model._meta
+            # Abstract model's fields are copied to child models, hence we will
+            # see the fields from the child models.
+            if opts.abstract:
+                continue
+            fields_with_relations = (
+                f for f in opts._get_fields(reverse=False, include_parents=False)
+                if f.is_relation and f.related_model is not None
+            )
+            for f in fields_with_relations:
+                if not isinstance(f.remote_field.model, str):
+                    related_objects_graph[f.remote_field.model._meta.concrete_model._meta].append(f)
+
+        for model in all_models:
+            # Set the relation_tree using the internal __dict__. In this way
+            # we avoid calling the cached property. In attribute lookup,
+            # __dict__ takes precedence over a data descriptor (such as
+            # @cached_property). This means that the _meta._relation_tree is
+            # only called if related_objects is not in __dict__.
+            related_objects = related_objects_graph[model._meta.concrete_model._meta]
+            model._meta.__dict__['_relation_tree'] = related_objects
+        # It seems it is possible that self is not in all_models, so guard
+        # against that with default for get().
+        return self.__dict__.get('_relation_tree', EMPTY_RELATION_TREE)
+
+    @cached_property
+    def _relation_tree(self):
+        return self._populate_directed_relation_graph()
+
+    def _expire_cache(self, forward=True, reverse=True):
+        # This method is usually called by apps.cache_clear(), when the
+        # registry is finalized, or when a new field is added.
+        if forward:
+            for cache_key in self.FORWARD_PROPERTIES:
+                if cache_key in self.__dict__:
+                    delattr(self, cache_key)
+        if reverse and not self.abstract:
+            for cache_key in self.REVERSE_PROPERTIES:
+                if cache_key in self.__dict__:
+                    delattr(self, cache_key)
+        self._get_fields_cache = {}
+
+    def get_fields(self, include_parents=True, include_hidden=False):
+        """
+        Return a list of fields associated to the model. By default, include
+        forward and reverse fields, fields derived from inheritance, but not
+        hidden fields. The returned fields can be changed using the parameters:
+
+        - include_parents: include fields derived from inheritance
+        - include_hidden:  include fields that have a related_name that
+                           starts with a "+"
+        """
+        if include_parents is False:
+            include_parents = PROXY_PARENTS
+        return self._get_fields(include_parents=include_parents, include_hidden=include_hidden)
+
+    def _get_fields(self, forward=True, reverse=True, include_parents=True, include_hidden=False,
+                    seen_models=None):
+        """
+        Internal helper function to return fields of the model.
+        * If forward=True, then fields defined on this model are returned.
+        * If reverse=True, then relations pointing to this model are returned.
+        * If include_hidden=True, then fields with is_hidden=True are returned.
+        * The include_parents argument toggles if fields from parent models
+          should be included. It has three values: True, False, and
+          PROXY_PARENTS. When set to PROXY_PARENTS, the call will return all
+          fields defined for the current model or any of its parents in the
+          parent chain to the model's concrete model.
+        """
+        if include_parents not in (True, False, PROXY_PARENTS):
+            raise TypeError("Invalid argument for include_parents: %s" % (include_parents,))
+        # This helper function is used to allow recursion in ``get_fields()``
+        # implementation and to provide a fast way for Django's internals to
+        # access specific subsets of fields.
+
+        # We must keep track of which models we have already seen. Otherwise we
+        # could include the same field multiple times from different models.
+        topmost_call = seen_models is None
+        if topmost_call:
+            seen_models = set()
+        seen_models.add(self.model)
+
+        # Creates a cache key composed of all arguments
+        cache_key = (forward, reverse, include_parents, include_hidden, topmost_call)
+
+        try:
+            # In order to avoid list manipulation. Always return a shallow copy
+            # of the results.
+            return self._get_fields_cache[cache_key]
+        except KeyError:
+            pass
+
+        fields = []
+        # Recursively call _get_fields() on each parent, with the same
+        # options provided in this call.
+        if include_parents is not False:
+            for parent in self.parents:
+                # In diamond inheritance it is possible that we see the same
+                # model from two different routes. In that case, avoid adding
+                # fields from the same parent again.
+                if parent in seen_models:
+                    continue
+                if (parent._meta.concrete_model != self.concrete_model and
+                        include_parents == PROXY_PARENTS):
+                    continue
+                for obj in parent._meta._get_fields(
+                        forward=forward, reverse=reverse, include_parents=include_parents,
+                        include_hidden=include_hidden, seen_models=seen_models):
+                    if not getattr(obj, 'parent_link', False) or obj.model == self.concrete_model:
+                        fields.append(obj)
+        if reverse and not self.proxy:
+            # Tree is computed once and cached until the app cache is expired.
+            # It is composed of a list of fields pointing to the current model
+            # from other models.
+            all_fields = self._relation_tree
+            for field in all_fields:
+                # If hidden fields should be included or the relation is not
+                # intentionally hidden, add to the fields dict.
+                if include_hidden or not field.remote_field.hidden:
+                    fields.append(field.remote_field)
+
+        if forward:
+            fields += self.local_fields
+            fields += self.local_many_to_many
+            # Private fields are recopied to each child model, and they get a
+            # different model as field.model in each child. Hence we have to
+            # add the private fields separately from the topmost call. If we
+            # did this recursively similar to local_fields, we would get field
+            # instances with field.model != self.model.
+            if topmost_call:
+                fields += self.private_fields
+
+        # In order to avoid list manipulation. Always
+        # return a shallow copy of the results
+        fields = make_immutable_fields_list("get_fields()", fields)
+
+        # Store result into cache for later access
+        self._get_fields_cache[cache_key] = fields
+        return fields
+
+    @cached_property
+    def _property_names(self):
+        """Return a set of the names of the properties defined on the model."""
+        names = []
+        for name in dir(self.model):
+            attr = inspect.getattr_static(self.model, name)
+            if isinstance(attr, property):
+                names.append(name)
+        return frozenset(names)

venv/lib/python3.7/site-packages/django/db/models/sql/datastructures.py

@@ -0,0 +1,170 @@
+"""
+Useful auxiliary data structures for query construction. Not useful outside
+the SQL domain.
+"""
+# for backwards-compatibility in Django 1.11
+from django.core.exceptions import EmptyResultSet  # NOQA: F401
+from django.db.models.sql.constants import INNER, LOUTER
+
+
+class MultiJoin(Exception):
+    """
+    Used by join construction code to indicate the point at which a
+    multi-valued join was attempted (if the caller wants to treat that
+    exceptionally).
+    """
+    def __init__(self, names_pos, path_with_names):
+        self.level = names_pos
+        # The path travelled, this includes the path to the multijoin.
+        self.names_with_path = path_with_names
+
+
+class Empty:
+    pass
+
+
+class Join:
+    """
+    Used by sql.Query and sql.SQLCompiler to generate JOIN clauses into the
+    FROM entry. For example, the SQL generated could be
+        LEFT OUTER JOIN "sometable" T1 ON ("othertable"."sometable_id" = "sometable"."id")
+
+    This class is primarily used in Query.alias_map. All entries in alias_map
+    must be Join compatible by providing the following attributes and methods:
+        - table_name (string)
+        - table_alias (possible alias for the table, can be None)
+        - join_type (can be None for those entries that aren't joined from
+          anything)
+        - parent_alias (which table is this join's parent, can be None similarly
+          to join_type)
+        - as_sql()
+        - relabeled_clone()
+    """
+    def __init__(self, table_name, parent_alias, table_alias, join_type,
+                 join_field, nullable, filtered_relation=None):
+        # Join table
+        self.table_name = table_name
+        self.parent_alias = parent_alias
+        # Note: table_alias is not necessarily known at instantiation time.
+        self.table_alias = table_alias
+        # LOUTER or INNER
+        self.join_type = join_type
+        # A list of 2-tuples to use in the ON clause of the JOIN.
+        # Each 2-tuple will create one join condition in the ON clause.
+        self.join_cols = join_field.get_joining_columns()
+        # Along which field (or ForeignObjectRel in the reverse join case)
+        self.join_field = join_field
+        # Is this join nullabled?
+        self.nullable = nullable
+        self.filtered_relation = filtered_relation
+
+    def as_sql(self, compiler, connection):
+        """
+        Generate the full
+           LEFT OUTER JOIN sometable ON sometable.somecol = othertable.othercol, params
+        clause for this join.
+        """
+        join_conditions = []
+        params = []
+        qn = compiler.quote_name_unless_alias
+        qn2 = connection.ops.quote_name
+
+        # Add a join condition for each pair of joining columns.
+        for lhs_col, rhs_col in self.join_cols:
+            join_conditions.append('%s.%s = %s.%s' % (
+                qn(self.parent_alias),
+                qn2(lhs_col),
+                qn(self.table_alias),
+                qn2(rhs_col),
+            ))
+
+        # Add a single condition inside parentheses for whatever
+        # get_extra_restriction() returns.
+        extra_cond = self.join_field.get_extra_restriction(
+            compiler.query.where_class, self.table_alias, self.parent_alias)
+        if extra_cond:
+            extra_sql, extra_params = compiler.compile(extra_cond)
+            join_conditions.append('(%s)' % extra_sql)
+            params.extend(extra_params)
+        if self.filtered_relation:
+            extra_sql, extra_params = compiler.compile(self.filtered_relation)
+            if extra_sql:
+                join_conditions.append('(%s)' % extra_sql)
+                params.extend(extra_params)
+        if not join_conditions:
+            # This might be a rel on the other end of an actual declared field.
+            declared_field = getattr(self.join_field, 'field', self.join_field)
+            raise ValueError(
+                "Join generated an empty ON clause. %s did not yield either "
+                "joining columns or extra restrictions." % declared_field.__class__
+            )
+        on_clause_sql = ' AND '.join(join_conditions)
+        alias_str = '' if self.table_alias == self.table_name else (' %s' % self.table_alias)
+        sql = '%s %s%s ON (%s)' % (self.join_type, qn(self.table_name), alias_str, on_clause_sql)
+        return sql, params
+
+    def relabeled_clone(self, change_map):
+        new_parent_alias = change_map.get(self.parent_alias, self.parent_alias)
+        new_table_alias = change_map.get(self.table_alias, self.table_alias)
+        if self.filtered_relation is not None:
+            filtered_relation = self.filtered_relation.clone()
+            filtered_relation.path = [change_map.get(p, p) for p in self.filtered_relation.path]
+        else:
+            filtered_relation = None
+        return self.__class__(
+            self.table_name, new_parent_alias, new_table_alias, self.join_type,
+            self.join_field, self.nullable, filtered_relation=filtered_relation,
+        )
+
+    def equals(self, other, with_filtered_relation):
+        return (
+            isinstance(other, self.__class__) and
+            self.table_name == other.table_name and
+            self.parent_alias == other.parent_alias and
+            self.join_field == other.join_field and
+            (not with_filtered_relation or self.filtered_relation == other.filtered_relation)
+        )
+
+    def __eq__(self, other):
+        return self.equals(other, with_filtered_relation=True)
+
+    def demote(self):
+        new = self.relabeled_clone({})
+        new.join_type = INNER
+        return new
+
+    def promote(self):
+        new = self.relabeled_clone({})
+        new.join_type = LOUTER
+        return new
+
+
+class BaseTable:
+    """
+    The BaseTable class is used for base table references in FROM clause. For
+    example, the SQL "foo" in
+        SELECT * FROM "foo" WHERE somecond
+    could be generated by this class.
+    """
+    join_type = None
+    parent_alias = None
+    filtered_relation = None
+
+    def __init__(self, table_name, alias):
+        self.table_name = table_name
+        self.table_alias = alias
+
+    def as_sql(self, compiler, connection):
+        alias_str = '' if self.table_alias == self.table_name else (' %s' % self.table_alias)
+        base_sql = compiler.quote_name_unless_alias(self.table_name)
+        return base_sql + alias_str, []
+
+    def relabeled_clone(self, change_map):
+        return self.__class__(self.table_name, change_map.get(self.table_alias, self.table_alias))
+
+    def equals(self, other, with_filtered_relation):
+        return (
+            isinstance(self, other.__class__) and
+            self.table_name == other.table_name and
+            self.table_alias == other.table_alias
+        )

venv/lib/python3.7/site-packages/django/db/models/sql/where.py

@@ -0,0 +1,228 @@
+"""
+Code to manage the creation and SQL rendering of 'where' constraints.
+"""
+
+from django.core.exceptions import EmptyResultSet
+from django.utils import tree
+from django.utils.functional import cached_property
+
+# Connection types
+AND = 'AND'
+OR = 'OR'
+
+
+class WhereNode(tree.Node):
+    """
+    An SQL WHERE clause.
+
+    The class is tied to the Query class that created it (in order to create
+    the correct SQL).
+
+    A child is usually an expression producing boolean values. Most likely the
+    expression is a Lookup instance.
+
+    However, a child could also be any class with as_sql() and either
+    relabeled_clone() method or relabel_aliases() and clone() methods and
+    contains_aggregate attribute.
+    """
+    default = AND
+    resolved = False
+    conditional = True
+
+    def split_having(self, negated=False):
+        """
+        Return two possibly None nodes: one for those parts of self that
+        should be included in the WHERE clause and one for those parts of
+        self that must be included in the HAVING clause.
+        """
+        if not self.contains_aggregate:
+            return self, None
+        in_negated = negated ^ self.negated
+        # If the effective connector is OR and this node contains an aggregate,
+        # then we need to push the whole branch to HAVING clause.
+        may_need_split = (
+            (in_negated and self.connector == AND) or
+            (not in_negated and self.connector == OR))
+        if may_need_split and self.contains_aggregate:
+            return None, self
+        where_parts = []
+        having_parts = []
+        for c in self.children:
+            if hasattr(c, 'split_having'):
+                where_part, having_part = c.split_having(in_negated)
+                if where_part is not None:
+                    where_parts.append(where_part)
+                if having_part is not None:
+                    having_parts.append(having_part)
+            elif c.contains_aggregate:
+                having_parts.append(c)
+            else:
+                where_parts.append(c)
+        having_node = self.__class__(having_parts, self.connector, self.negated) if having_parts else None
+        where_node = self.__class__(where_parts, self.connector, self.negated) if where_parts else None
+        return where_node, having_node
+
+    def as_sql(self, compiler, connection):
+        """
+        Return the SQL version of the where clause and the value to be
+        substituted in. Return '', [] if this node matches everything,
+        None, [] if this node is empty, and raise EmptyResultSet if this
+        node can't match anything.
+        """
+        result = []
+        result_params = []
+        if self.connector == AND:
+            full_needed, empty_needed = len(self.children), 1
+        else:
+            full_needed, empty_needed = 1, len(self.children)
+
+        for child in self.children:
+            try:
+                sql, params = compiler.compile(child)
+            except EmptyResultSet:
+                empty_needed -= 1
+            else:
+                if sql:
+                    result.append(sql)
+                    result_params.extend(params)
+                else:
+                    full_needed -= 1
+            # Check if this node matches nothing or everything.
+            # First check the amount of full nodes and empty nodes
+            # to make this node empty/full.
+            # Now, check if this node is full/empty using the
+            # counts.
+            if empty_needed == 0:
+                if self.negated:
+                    return '', []
+                else:
+                    raise EmptyResultSet
+            if full_needed == 0:
+                if self.negated:
+                    raise EmptyResultSet
+                else:
+                    return '', []
+        conn = ' %s ' % self.connector
+        sql_string = conn.join(result)
+        if sql_string:
+            if self.negated:
+                # Some backends (Oracle at least) need parentheses
+                # around the inner SQL in the negated case, even if the
+                # inner SQL contains just a single expression.
+                sql_string = 'NOT (%s)' % sql_string
+            elif len(result) > 1 or self.resolved:
+                sql_string = '(%s)' % sql_string
+        return sql_string, result_params
+
+    def get_group_by_cols(self):
+        cols = []
+        for child in self.children:
+            cols.extend(child.get_group_by_cols())
+        return cols
+
+    def get_source_expressions(self):
+        return self.children[:]
+
+    def set_source_expressions(self, children):
+        assert len(children) == len(self.children)
+        self.children = children
+
+    def relabel_aliases(self, change_map):
+        """
+        Relabel the alias values of any children. 'change_map' is a dictionary
+        mapping old (current) alias values to the new values.
+        """
+        for pos, child in enumerate(self.children):
+            if hasattr(child, 'relabel_aliases'):
+                # For example another WhereNode
+                child.relabel_aliases(change_map)
+            elif hasattr(child, 'relabeled_clone'):
+                self.children[pos] = child.relabeled_clone(change_map)
+
+    def clone(self):
+        """
+        Create a clone of the tree. Must only be called on root nodes (nodes
+        with empty subtree_parents). Childs must be either (Constraint, lookup,
+        value) tuples, or objects supporting .clone().
+        """
+        clone = self.__class__._new_instance(
+            children=[], connector=self.connector, negated=self.negated)
+        for child in self.children:
+            if hasattr(child, 'clone'):
+                clone.children.append(child.clone())
+            else:
+                clone.children.append(child)
+        return clone
+
+    def relabeled_clone(self, change_map):
+        clone = self.clone()
+        clone.relabel_aliases(change_map)
+        return clone
+
+    @classmethod
+    def _contains_aggregate(cls, obj):
+        if isinstance(obj, tree.Node):
+            return any(cls._contains_aggregate(c) for c in obj.children)
+        return obj.contains_aggregate
+
+    @cached_property
+    def contains_aggregate(self):
+        return self._contains_aggregate(self)
+
+    @classmethod
+    def _contains_over_clause(cls, obj):
+        if isinstance(obj, tree.Node):
+            return any(cls._contains_over_clause(c) for c in obj.children)
+        return obj.contains_over_clause
+
+    @cached_property
+    def contains_over_clause(self):
+        return self._contains_over_clause(self)
+
+    @property
+    def is_summary(self):
+        return any(child.is_summary for child in self.children)
+
+    def resolve_expression(self, *args, **kwargs):
+        clone = self.clone()
+        clone.resolved = True
+        return clone
+
+
+class NothingNode:
+    """A node that matches nothing."""
+    contains_aggregate = False
+
+    def as_sql(self, compiler=None, connection=None):
+        raise EmptyResultSet
+
+
+class ExtraWhere:
+    # The contents are a black box - assume no aggregates are used.
+    contains_aggregate = False
+
+    def __init__(self, sqls, params):
+        self.sqls = sqls
+        self.params = params
+
+    def as_sql(self, compiler=None, connection=None):
+        sqls = ["(%s)" % sql for sql in self.sqls]
+        return " AND ".join(sqls), list(self.params or ())
+
+
+class SubqueryConstraint:
+    # Even if aggregates would be used in a subquery, the outer query isn't
+    # interested about those.
+    contains_aggregate = False
+
+    def __init__(self, alias, columns, targets, query_object):
+        self.alias = alias
+        self.columns = columns
+        self.targets = targets
+        self.query_object = query_object
+
+    def as_sql(self, compiler, connection):
+        query = self.query_object
+        query.set_values(self.targets)
+        query_compiler = query.get_compiler(connection=connection)
+        return query_compiler.as_subquery_condition(self.alias, self.columns, compiler)

venv/lib/python3.7/site-packages/django/db/models/utils.py

@@ -0,0 +1,21 @@
+def make_model_tuple(model):
+    """
+    Take a model or a string of the form "app_label.ModelName" and return a
+    corresponding ("app_label", "modelname") tuple. If a tuple is passed in,
+    assume it's a valid model tuple already and return it unchanged.
+    """
+    try:
+        if isinstance(model, tuple):
+            model_tuple = model
+        elif isinstance(model, str):
+            app_label, model_name = model.split(".")
+            model_tuple = app_label, model_name.lower()
+        else:
+            model_tuple = model._meta.app_label, model._meta.model_name
+        assert len(model_tuple) == 2
+        return model_tuple
+    except (ValueError, AssertionError):
+        raise ValueError(
+            "Invalid model reference '%s'. String model references "
+            "must be of the form 'app_label.ModelName'." % model
+        )