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Fixed #17001 -- Custom querysets for prefetch_related. 

This patch introduces the Prefetch object which allows customizing prefetch
operations.

This enables things like filtering prefetched relations, calling select_related
from a prefetched relation, or prefetching the same relation multiple times
with different querysets.

When a Prefetch instance specifies a to_attr argument, the result is stored
in a list rather than a QuerySet. This has the fortunate consequence of being
significantly faster. The preformance improvement is due to the fact that we
save the costly creation of a QuerySet instance.

Thanks @akaariai for the original patch and @bmispelon and @timgraham
for the reviews.
This commit is contained in:
Loic Bistuer 2013-11-07 00:25:05 +07:00 committed by Anssi Kääriäinen
parent b1b04df065
commit f51c1f5900
9 changed files with 616 additions and 65 deletions
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18
django/contrib/contenttypes/generic.py
View File

@ -76,7 +76,10 @@ class GenericForeignKey(six.with_metaclass(RenameGenericForeignKeyMethods)):
# This should never happen. I love comments like this, don't you?
raise Exception("Impossible arguments to GFK.get_content_type!")
def get_prefetch_queryset(self, instances):
def get_prefetch_queryset(self, instances, queryset=None):
if queryset is not None:
raise ValueError("Custom queryset can't be used for this lookup.")
# For efficiency, group the instances by content type and then do one
# query per model
fk_dict = defaultdict(set)
@ -348,17 +351,22 @@ def create_generic_related_manager(superclass):
db = self._db or router.db_for_read(self.model, instance=self.instance)
return super(GenericRelatedObjectManager, self).get_queryset().using(db).filter(**self.core_filters)
def get_prefetch_queryset(self, instances):
db = self._db or router.db_for_read(self.model, instance=instances[0])
def get_prefetch_queryset(self, instances, queryset=None):
if queryset is None:
queryset = super(GenericRelatedObjectManager, self).get_queryset()
queryset._add_hints(instance=instances[0])
queryset = queryset.using(queryset._db or self._db)
query = {
'%s__pk' % self.content_type_field_name: self.content_type.id,
'%s__in' % self.object_id_field_name: set(obj._get_pk_val() for obj in instances)
}
qs = super(GenericRelatedObjectManager, self).get_queryset().using(db).filter(**query)
# We (possibly) need to convert object IDs to the type of the
# instances' PK in order to match up instances:
object_id_converter = instances[0]._meta.pk.to_python
return (qs,
return (queryset.filter(**query),
lambda relobj: object_id_converter(getattr(relobj, self.object_id_field_name)),
lambda obj: obj._get_pk_val(),
False,

2
django/db/models/__init__.py
View File

@ -4,7 +4,7 @@ from django.core.exceptions import ObjectDoesNotExist, ImproperlyConfigured # N
from django.db.models.loading import ( # NOQA
get_apps, get_app_path, get_app_paths, get_app, get_models, get_model,
register_models, UnavailableApp)
from django.db.models.query import Q, QuerySet # NOQA
from django.db.models.query import Q, QuerySet, Prefetch # NOQA
from django.db.models.expressions import F # NOQA
from django.db.models.manager import Manager # NOQA
from django.db.models.base import Model # NOQA

51
django/db/models/fields/related.py
View File

@ -162,7 +162,10 @@ class SingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjectDescri
def get_queryset(self, **hints):
return self.related.model._base_manager.db_manager(hints=hints)
def get_prefetch_queryset(self, instances):
def get_prefetch_queryset(self, instances, queryset=None):
if queryset is not None:
raise ValueError("Custom queryset can't be used for this lookup.")
rel_obj_attr = attrgetter(self.related.field.attname)
instance_attr = lambda obj: obj._get_pk_val()
instances_dict = dict((instance_attr(inst), inst) for inst in instances)
@ -264,7 +267,10 @@ class ReverseSingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjec
else:
return QuerySet(self.field.rel.to, hints=hints)
def get_prefetch_queryset(self, instances):
def get_prefetch_queryset(self, instances, queryset=None):
if queryset is not None:
raise ValueError("Custom queryset can't be used for this lookup.")
rel_obj_attr = self.field.get_foreign_related_value
instance_attr = self.field.get_local_related_value
instances_dict = dict((instance_attr(inst), inst) for inst in instances)
@ -397,23 +403,26 @@ def create_foreign_related_manager(superclass, rel_field, rel_model):
qs._known_related_objects = {rel_field: {self.instance.pk: self.instance}}
return qs
def get_prefetch_queryset(self, instances):
def get_prefetch_queryset(self, instances, queryset=None):
if queryset is None:
queryset = super(RelatedManager, self).get_queryset()
queryset._add_hints(instance=instances[0])
queryset = queryset.using(queryset._db or self._db)
rel_obj_attr = rel_field.get_local_related_value
instance_attr = rel_field.get_foreign_related_value
instances_dict = dict((instance_attr(inst), inst) for inst in instances)
query = {'%s__in' % rel_field.name: instances}
qs = super(RelatedManager, self).get_queryset()
qs._add_hints(instance=instances[0])
if self._db:
qs = qs.using(self._db)
qs = qs.filter(**query)
queryset = queryset.filter(**query)
# Since we just bypassed this class' get_queryset(), we must manage
# the reverse relation manually.
for rel_obj in qs:
for rel_obj in queryset:
instance = instances_dict[rel_obj_attr(rel_obj)]
setattr(rel_obj, rel_field.name, instance)
cache_name = rel_field.related_query_name()
return qs, rel_obj_attr, instance_attr, False, cache_name
return queryset, rel_obj_attr, instance_attr, False, cache_name
def add(self, *objs):
objs = list(objs)
@ -563,15 +572,15 @@ def create_many_related_manager(superclass, rel):
qs = qs.using(self._db)
return qs._next_is_sticky().filter(**self.core_filters)
def get_prefetch_queryset(self, instances):
instance = instances[0]
db = self._db or router.db_for_read(instance.__class__, instance=instance)
def get_prefetch_queryset(self, instances, queryset=None):
if queryset is None:
queryset = super(ManyRelatedManager, self).get_queryset()
queryset._add_hints(instance=instances[0])
queryset = queryset.using(queryset._db or self._db)
query = {'%s__in' % self.query_field_name: instances}
qs = super(ManyRelatedManager, self).get_queryset()
qs._add_hints(instance=instance)
if self._db:
qs = qs.using(db)
qs = qs._next_is_sticky().filter(**query)
queryset = queryset._next_is_sticky().filter(**query)
# M2M: need to annotate the query in order to get the primary model
# that the secondary model was actually related to. We know that
@ -582,12 +591,12 @@ def create_many_related_manager(superclass, rel):
# dealing with PK values.
fk = self.through._meta.get_field(self.source_field_name)
join_table = self.through._meta.db_table
connection = connections[db]
connection = connections[queryset.db]
qn = connection.ops.quote_name
qs = qs.extra(select=dict(
queryset = queryset.extra(select=dict(
('_prefetch_related_val_%s' % f.attname,
'%s.%s' % (qn(join_table), qn(f.column))) for f in fk.local_related_fields))
return (qs,
return (queryset,
lambda result: tuple(getattr(result, '_prefetch_related_val_%s' % f.attname) for f in fk.local_related_fields),
lambda inst: tuple(getattr(inst, f.attname) for f in fk.foreign_related_fields),
False,

141
django/db/models/query.py
View File

@ -1619,6 +1619,59 @@ class RawQuerySet(object):
return self._model_fields
class Prefetch(object):
def __init__(self, lookup, queryset=None, to_attr=None):
# `prefetch_through` is the path we traverse to perform the prefetch.
self.prefetch_through = lookup
# `prefetch_to` is the path to the attribute that stores the result.
self.prefetch_to = lookup
if to_attr:
self.prefetch_to = LOOKUP_SEP.join(lookup.split(LOOKUP_SEP)[:-1] + [to_attr])
self.queryset = queryset
self.to_attr = to_attr
def add_prefix(self, prefix):
self.prefetch_through = LOOKUP_SEP.join([prefix, self.prefetch_through])
self.prefetch_to = LOOKUP_SEP.join([prefix, self.prefetch_to])
def get_current_prefetch_through(self, level):
return LOOKUP_SEP.join(self.prefetch_through.split(LOOKUP_SEP)[:level + 1])
def get_current_prefetch_to(self, level):
return LOOKUP_SEP.join(self.prefetch_to.split(LOOKUP_SEP)[:level + 1])
def get_current_to_attr(self, level):
parts = self.prefetch_to.split(LOOKUP_SEP)
to_attr = parts[level]
to_list = self.to_attr and level == len(parts) - 1
return to_attr, to_list
def get_current_queryset(self, level):
if self.get_current_prefetch_to(level) == self.prefetch_to:
return self.queryset
return None
def __eq__(self, other):
if isinstance(other, Prefetch):
return self.prefetch_to == other.prefetch_to
return False
def normalize_prefetch_lookups(lookups, prefix=None):
"""
Helper function that normalize lookups into Prefetch objects.
"""
ret = []
for lookup in lookups:
if not isinstance(lookup, Prefetch):
lookup = Prefetch(lookup)
if prefix:
lookup.add_prefix(prefix)
ret.append(lookup)
return ret
def prefetch_related_objects(result_cache, related_lookups):
"""
Helper function for prefetch_related functionality
@ -1626,13 +1679,15 @@ def prefetch_related_objects(result_cache, related_lookups):
Populates prefetched objects caches for a list of results
from a QuerySet
"""
if len(result_cache) == 0:
return # nothing to do
related_lookups = normalize_prefetch_lookups(related_lookups)
# We need to be able to dynamically add to the list of prefetch_related
# lookups that we look up (see below). So we need some book keeping to
# ensure we don't do duplicate work.
done_lookups = set() # list of lookups like foo__bar__baz
done_queries = {} # dictionary of things like 'foo__bar': [results]
auto_lookups = [] # we add to this as we go through.
@ -1640,25 +1695,27 @@ def prefetch_related_objects(result_cache, related_lookups):
all_lookups = itertools.chain(related_lookups, auto_lookups)
for lookup in all_lookups:
if lookup in done_lookups:
# We've done exactly this already, skip the whole thing
if lookup.prefetch_to in done_queries:
if lookup.queryset:
raise ValueError("'%s' lookup was already seen with a different queryset. "
"You may need to adjust the ordering of your lookups." % lookup.prefetch_to)
continue
done_lookups.add(lookup)
# Top level, the list of objects to decorate is the result cache
# from the primary QuerySet. It won't be for deeper levels.
obj_list = result_cache
attrs = lookup.split(LOOKUP_SEP)
for level, attr in enumerate(attrs):
through_attrs = lookup.prefetch_through.split(LOOKUP_SEP)
for level, through_attr in enumerate(through_attrs):
# Prepare main instances
if len(obj_list) == 0:
break
current_lookup = LOOKUP_SEP.join(attrs[:level + 1])
if current_lookup in done_queries:
prefetch_to = lookup.get_current_prefetch_to(level)
if prefetch_to in done_queries:
# Skip any prefetching, and any object preparation
obj_list = done_queries[current_lookup]
obj_list = done_queries[prefetch_to]
continue
# Prepare objects:
@ -1685,34 +1742,40 @@ def prefetch_related_objects(result_cache, related_lookups):
# We assume that objects retrieved are homogenous (which is the premise
# of prefetch_related), so what applies to first object applies to all.
first_obj = obj_list[0]
prefetcher, descriptor, attr_found, is_fetched = get_prefetcher(first_obj, attr)
prefetcher, descriptor, attr_found, is_fetched = get_prefetcher(first_obj, through_attr)
if not attr_found:
raise AttributeError("Cannot find '%s' on %s object, '%s' is an invalid "
"parameter to prefetch_related()" %
(attr, first_obj.__class__.__name__, lookup))
(through_attr, first_obj.__class__.__name__, lookup.prefetch_through))
if level == len(attrs) - 1 and prefetcher is None:
if level == len(through_attrs) - 1 and prefetcher is None:
# Last one, this *must* resolve to something that supports
# prefetching, otherwise there is no point adding it and the
# developer asking for it has made a mistake.
raise ValueError("'%s' does not resolve to a item that supports "
"prefetching - this is an invalid parameter to "
"prefetch_related()." % lookup)
"prefetch_related()." % lookup.prefetch_through)
if prefetcher is not None and not is_fetched:
obj_list, additional_prl = prefetch_one_level(obj_list, prefetcher, attr)
obj_list, additional_lookups = prefetch_one_level(obj_list, prefetcher, lookup, level)
# We need to ensure we don't keep adding lookups from the
# same relationships to stop infinite recursion. So, if we
# are already on an automatically added lookup, don't add
# the new lookups from relationships we've seen already.
if not (lookup in auto_lookups and
descriptor in followed_descriptors):
for f in additional_prl:
new_prl = LOOKUP_SEP.join([current_lookup, f])
auto_lookups.append(new_prl)
done_queries[current_lookup] = obj_list
if not (lookup in auto_lookups and descriptor in followed_descriptors):
done_queries[prefetch_to] = obj_list
auto_lookups.extend(normalize_prefetch_lookups(additional_lookups, prefetch_to))
followed_descriptors.add(descriptor)
elif isinstance(getattr(first_obj, through_attr), list):
# The current part of the lookup relates to a custom Prefetch.
# This means that obj.attr is a list of related objects, and
# thus we must turn the obj.attr lists into a single related
# object list.
new_list = []
for obj in obj_list:
new_list.extend(getattr(obj, through_attr))
obj_list = new_list
else:
# Either a singly related object that has already been fetched
# (e.g. via select_related), or hopefully some other property
@ -1724,7 +1787,7 @@ def prefetch_related_objects(result_cache, related_lookups):
new_obj_list = []
for obj in obj_list:
try:
new_obj = getattr(obj, attr)
new_obj = getattr(obj, through_attr)
except exceptions.ObjectDoesNotExist:
continue
if new_obj is None:
@ -1755,6 +1818,11 @@ def get_prefetcher(instance, attr):
try:
rel_obj = getattr(instance, attr)
attr_found = True
# If we are following a lookup path which leads us through a previous
# fetch from a custom Prefetch then we might end up into a list
# instead of related qs. This means the objects are already fetched.
if isinstance(rel_obj, list):
is_fetched = True
except AttributeError:
pass
else:
@ -1776,7 +1844,7 @@ def get_prefetcher(instance, attr):
return prefetcher, rel_obj_descriptor, attr_found, is_fetched
def prefetch_one_level(instances, prefetcher, attname):
def prefetch_one_level(instances, prefetcher, lookup, level):
"""
Helper function for prefetch_related_objects
@ -1799,14 +1867,14 @@ def prefetch_one_level(instances, prefetcher, attname):
# The 'values to be matched' must be hashable as they will be used
# in a dictionary.
rel_qs, rel_obj_attr, instance_attr, single, cache_name =\
prefetcher.get_prefetch_queryset(instances)
rel_qs, rel_obj_attr, instance_attr, single, cache_name = (
prefetcher.get_prefetch_queryset(instances, lookup.get_current_queryset(level)))
# We have to handle the possibility that the default manager itself added
# prefetch_related lookups to the QuerySet we just got back. We don't want to
# trigger the prefetch_related functionality by evaluating the query.
# Rather, we need to merge in the prefetch_related lookups.
additional_prl = getattr(rel_qs, '_prefetch_related_lookups', [])
if additional_prl:
additional_lookups = getattr(rel_qs, '_prefetch_related_lookups', [])
if additional_lookups:
# Don't need to clone because the manager should have given us a fresh
# instance, so we access an internal instead of using public interface
# for performance reasons.
@ -1826,12 +1894,15 @@ def prefetch_one_level(instances, prefetcher, attname):
# Need to assign to single cache on instance
setattr(obj, cache_name, vals[0] if vals else None)
else:
# Multi, attribute represents a manager with an .all() method that
# returns a QuerySet
qs = getattr(obj, attname).all()
qs._result_cache = vals
# We don't want the individual qs doing prefetch_related now, since we
# have merged this into the current work.
qs._prefetch_done = True
obj._prefetched_objects_cache[cache_name] = qs
return all_related_objects, additional_prl
to_attr, to_list = lookup.get_current_to_attr(level)
if to_list:
setattr(obj, to_attr, vals)
else:
# Cache in the QuerySet.all().
qs = getattr(obj, to_attr).all()
qs._result_cache = vals
# We don't want the individual qs doing prefetch_related now,
# since we have merged this into the current work.
qs._prefetch_done = True
obj._prefetched_objects_cache[cache_name] = qs
return all_related_objects, additional_lookups

29
docs/ref/models/queries.txt
View File

@ -129,3 +129,32 @@ In general, ``Q() objects`` make it possible to define and reuse conditions.
This permits the :ref:`construction of complex database queries
<complex-lookups-with-q>` using ``|`` (``OR``) and ``&`` (``AND``) operators;
in particular, it is not otherwise possible to use ``OR`` in ``QuerySets``.
``Prefetch()`` objects
======================
.. versionadded:: 1.7
.. class:: Prefetch(lookup, queryset=None, to_attr=None)
The ``Prefetch()`` object can be used to control the operation of
:meth:`~django.db.models.query.QuerySet.prefetch_related()`.
The ``lookup`` argument describes the relations to follow and works the same
as the string based lookups passed to
:meth:`~django.db.models.query.QuerySet.prefetch_related()`.
The ``queryset`` argument supplies a base ``QuerySet`` for the given lookup.
This is useful to further filter down the prefetch operation, or to call
:meth:`~django.db.models.query.QuerySet.select_related()` from the prefetched
relation, hence reducing the number of queries even further.
The ``to_attr`` argument sets the result of the prefetch operation to a custom
attribute.
.. note::
When using ``to_attr`` the prefetched result is stored in a list.
This can provide a significant speed improvement over traditional
``prefetch_related`` calls which store the cached result within a
``QuerySet`` instance.

87
docs/ref/models/querysets.txt
View File

@ -898,7 +898,7 @@ objects have already been fetched, and it will skip fetching them again.
Chaining ``prefetch_related`` calls will accumulate the lookups that are
prefetched. To clear any ``prefetch_related`` behavior, pass ``None`` as a
parameter::
parameter:
>>> non_prefetched = qs.prefetch_related(None)
@ -925,6 +925,91 @@ profile for your use case!
Note that if you use ``iterator()`` to run the query, ``prefetch_related()``
calls will be ignored since these two optimizations do not make sense together.
.. versionadded:: 1.7
You can use the :class:`~django.db.models.Prefetch` object to further control
the prefetch operation.
In its simplest form ``Prefetch`` is equivalent to the traditional string based
lookups:
>>> Restaurant.objects.prefetch_related(Prefetch('pizzas__toppings'))
You can provide a custom queryset with the optional ``queryset`` argument.
This can be used to change the default ordering of the queryset:
>>> Restaurant.objects.prefetch_related(
... Prefetch('pizzas__toppings', queryset=Toppings.objects.order_by('name')))
Or to call :meth:`~django.db.models.query.QuerySet.select_related()` when
applicable to reduce the number of queries even further:
>>> Pizza.objects.prefetch_related(
... Prefetch('restaurants', queryset=Restaurant.objects.select_related('best_pizza')))
You can also assign the prefetched result to a custom attribute with the optional
``to_attr`` argument. The result will be stored directly in a list.
This allows prefetching the same relation multiple times with a different
``QuerySet``; for instance:
>>> vegetarian_pizzas = Pizza.objects.filter(vegetarian=True)
>>> Restaurant.objects.prefetch_related(
... Prefetch('pizzas', to_attr('menu')),
... Prefetch('pizzas', queryset=vegetarian_pizzas to_attr='vegetarian_menu'))
Lookups created with custom ``to_attr`` can still be traversed as usual by other
lookups:
>>> vegetarian_pizzas = Pizza.objects.filter(vegetarian=True)
>>> Restaurant.objects.prefetch_related(
... Prefetch('pizzas', queryset=vegetarian_pizzas to_attr='vegetarian_menu'),
... 'vegetarian_menu__toppings')
Using ``to_attr`` is recommended when filtering down the prefetch result as it is
less ambiguous than storing a filtered result in the related manager's cache:
>>> queryset = Pizza.objects.filter(vegetarian=True)
>>>
>>> # Recommended:
>>> restaurants = Restaurant.objects.prefetch_related(
... Prefetch('pizzas', to_attr='vegetarian_pizzas' queryset=queryset))
>>> vegetarian_pizzas = restaurants[0].vegetarian_pizzas
>>>
>>> # Not recommended:
>>> restaurants = Restaurant.objects.prefetch_related(
... Prefetch('pizzas', queryset=queryset))
>>> vegetarian_pizzas = restaurants[0].pizzas.all()
.. note::
The ordering of lookups matters.
Take the following examples:
>>> prefetch_related('pizzas__toppings', 'pizzas')
This works even though it's unordered because ``'pizzas__toppings'``
already contains all the needed information, therefore the second argument
``'pizzas'`` is actually redundant.
>>> prefetch_related('pizzas__toppings', Prefetch('pizzas', queryset=Pizza.objects.all()))
This will raise a ``ValueError`` because of the attempt to redefine the
queryset of a previously seen lookup. Note that an implicit queryset was
created to traverse ``'pizzas'`` as part of the ``'pizzas__toppings'``
lookup.
>>> prefetch_related('pizza_list__toppings', Prefetch('pizzas', to_attr='pizza_list'))
This will trigger an ``AttributeError`` because ``'pizza_list'`` doesn't exist yet
when ``'pizza_list__toppings'`` is being processed.
This consideration is not limited to the use of ``Prefetch`` objects. Some
advanced techniques may require that the lookups be performed in a
specific order to avoid creating extra queries; therefore it's recommended
to always carefully order ``prefetch_related`` arguments.
extra
~~~~~

15
docs/releases/1.7.txt
View File

@ -98,6 +98,21 @@ Using a custom manager when traversing reverse relations
It is now possible to :ref:`specify a custom manager
<using-custom-reverse-manager>` when traversing a reverse relationship.
New ``Prefetch`` object for advanced ``prefetch_related`` operations.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The new :class:`~django.db.models.Prefetch` object allows customizing
prefetch operations.
You can specify the ``QuerySet`` used to traverse a given relation
or customize the storage location of prefetch results.
This enables things like filtering prefetched relations, calling
:meth:`~django.db.models.query.QuerySet.select_related()` from a prefetched
relation, or prefetching the same relation multiple times with different
querysets. See :meth:`~django.db.models.query.QuerySet.prefetch_related()`
for more details.
Admin shortcuts support time zones
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

10
tests/prefetch_related/models.py
View File

@ -137,6 +137,9 @@ class TaggedItem(models.Model):
def __str__(self):
return self.tag
class Meta:
ordering = ['id']
class Bookmark(models.Model):
url = models.URLField()
@ -146,6 +149,9 @@ class Bookmark(models.Model):
object_id_field='favorite_fkey',
related_name='favorite_bookmarks')
class Meta:
ordering = ['id']
class Comment(models.Model):
comment = models.TextField()
@ -155,12 +161,16 @@ class Comment(models.Model):
object_pk = models.TextField()
content_object = generic.GenericForeignKey(ct_field="content_type", fk_field="object_pk")
class Meta:
ordering = ['id']
## Models for lookup ordering tests
class House(models.Model):
address = models.CharField(max_length=255)
owner = models.ForeignKey('Person', null=True)
class Meta:
ordering = ['id']

328
tests/prefetch_related/tests.py
View File

@ -2,6 +2,7 @@ from __future__ import unicode_literals
from django.contrib.contenttypes.models import ContentType
from django.db import connection
from django.db.models import Prefetch
from django.test import TestCase
from django.test.utils import override_settings
from django.utils import six
@ -13,9 +14,7 @@ from .models import (Author, Book, Reader, Qualification, Teacher, Department,
class PrefetchRelatedTests(TestCase):
def setUp(self):
self.book1 = Book.objects.create(title="Poems")
self.book2 = Book.objects.create(title="Jane Eyre")
self.book3 = Book.objects.create(title="Wuthering Heights")
@ -207,6 +206,292 @@ class PrefetchRelatedTests(TestCase):
self.assertTrue("name" in str(cm.exception))
class CustomPrefetchTests(TestCase):
@classmethod
def traverse_qs(cls, obj_iter, path):
"""
Helper method that returns a list containing a list of the objects in the
obj_iter. Then for each object in the obj_iter, the path will be
recursively travelled and the found objects are added to the return value.
"""
ret_val = []
if hasattr(obj_iter, 'all'):
obj_iter = obj_iter.all()
try:
iter(obj_iter)
except TypeError:
obj_iter = [obj_iter]
for obj in obj_iter:
rel_objs = []
for part in path:
if not part:
continue
rel_objs.extend(cls.traverse_qs(getattr(obj, part[0]), [part[1:]]))
ret_val.append((obj, rel_objs))
return ret_val
def setUp(self):
self.person1 = Person.objects.create(name="Joe")
self.person2 = Person.objects.create(name="Mary")
self.house1 = House.objects.create(address="123 Main St", owner=self.person1)
self.house2 = House.objects.create(address="45 Side St", owner=self.person1)
self.house3 = House.objects.create(address="6 Downing St", owner=self.person2)
self.house4 = House.objects.create(address="7 Regents St", owner=self.person2)
self.room1_1 = Room.objects.create(name="Dining room", house=self.house1)
self.room1_2 = Room.objects.create(name="Lounge", house=self.house1)
self.room1_3 = Room.objects.create(name="Kitchen", house=self.house1)
self.room2_1 = Room.objects.create(name="Dining room", house=self.house2)
self.room2_2 = Room.objects.create(name="Lounge", house=self.house2)
self.room2_3 = Room.objects.create(name="Kitchen", house=self.house2)
self.room3_1 = Room.objects.create(name="Dining room", house=self.house3)
self.room3_2 = Room.objects.create(name="Lounge", house=self.house3)
self.room3_3 = Room.objects.create(name="Kitchen", house=self.house3)
self.room4_1 = Room.objects.create(name="Dining room", house=self.house4)
self.room4_2 = Room.objects.create(name="Lounge", house=self.house4)
self.room4_3 = Room.objects.create(name="Kitchen", house=self.house4)
self.person1.houses.add(self.house1, self.house2)
self.person2.houses.add(self.house3, self.house4)
def test_traverse_qs(self):
qs = Person.objects.prefetch_related('houses')
related_objs_normal = [list(p.houses.all()) for p in qs],
related_objs_from_traverse = [[inner[0] for inner in o[1]]
for o in self.traverse_qs(qs, [['houses']])]
self.assertEqual(related_objs_normal, (related_objs_from_traverse,))
def test_ambiguous(self):
# Ambiguous.
with self.assertRaises(ValueError):
self.traverse_qs(
Person.objects.prefetch_related('houses__rooms', Prefetch('houses', queryset=House.objects.all())),
[['houses', 'rooms']]
)
with self.assertRaises(AttributeError):
self.traverse_qs(
Person.objects.prefetch_related('houses_list__rooms', Prefetch('houses', queryset=House.objects.all(), to_attr='houses_lst')),
[['houses', 'rooms']]
)
# Not ambiguous.
self.traverse_qs(
Person.objects.prefetch_related('houses__rooms', 'houses'),
[['houses', 'rooms']]
)
self.traverse_qs(
Person.objects.prefetch_related('houses__rooms', Prefetch('houses', queryset=House.objects.all(), to_attr='houses_lst')),
[['houses', 'rooms']]
)
def test_m2m(self):
# Control lookups.
with self.assertNumQueries(2):
lst1 = self.traverse_qs(
Person.objects.prefetch_related('houses'),
[['houses']]
)
# Test lookups.
with self.assertNumQueries(2):
lst2 = self.traverse_qs(
Person.objects.prefetch_related(Prefetch('houses')),
[['houses']]
)
self.assertEqual(lst1, lst2)
with self.assertNumQueries(2):
lst2 = self.traverse_qs(
Person.objects.prefetch_related(Prefetch('houses', to_attr='houses_lst')),
[['houses_lst']]
)
self.assertEqual(lst1, lst2)
def test_reverse_m2m(self):
# Control lookups.
with self.assertNumQueries(2):
lst1 = self.traverse_qs(
House.objects.prefetch_related('occupants'),
[['occupants']]
)
# Test lookups.
with self.assertNumQueries(2):
lst2 = self.traverse_qs(
House.objects.prefetch_related(Prefetch('occupants')),
[['occupants']]
)
self.assertEqual(lst1, lst2)
with self.assertNumQueries(2):
lst2 = self.traverse_qs(
House.objects.prefetch_related(Prefetch('occupants', to_attr='occupants_lst')),
[['occupants_lst']]
)
self.assertEqual(lst1, lst2)
def test_m2m_through_fk(self):
# Control lookups.
with self.assertNumQueries(3):
lst1 = self.traverse_qs(
Room.objects.prefetch_related('house__occupants'),
[['house', 'occupants']]
)
# Test lookups.
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
Room.objects.prefetch_related(Prefetch('house__occupants')),
[['house', 'occupants']]
)
self.assertEqual(lst1, lst2)
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
Room.objects.prefetch_related(Prefetch('house__occupants', to_attr='occupants_lst')),
[['house', 'occupants_lst']]
)
self.assertEqual(lst1, lst2)
def test_m2m_through_gfk(self):
TaggedItem.objects.create(tag="houses", content_object=self.house1)
TaggedItem.objects.create(tag="houses", content_object=self.house2)
# Control lookups.
with self.assertNumQueries(3):
lst1 = self.traverse_qs(
TaggedItem.objects.filter(tag='houses').prefetch_related('content_object__rooms'),
[['content_object', 'rooms']]
)
# Test lookups.
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
TaggedItem.objects.prefetch_related(
Prefetch('content_object'),
Prefetch('content_object__rooms', to_attr='rooms_lst')
),
[['content_object', 'rooms_lst']]
)
self.assertEqual(lst1, lst2)
def test_o2m_through_m2m(self):
# Control lookups.
with self.assertNumQueries(3):
lst1 = self.traverse_qs(
Person.objects.prefetch_related('houses', 'houses__rooms'),
[['houses', 'rooms']]
)
# Test lookups.
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
Person.objects.prefetch_related(Prefetch('houses'), 'houses__rooms'),
[['houses', 'rooms']]
)
self.assertEqual(lst1, lst2)
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
Person.objects.prefetch_related(Prefetch('houses'), Prefetch('houses__rooms')),
[['houses', 'rooms']]
)
self.assertEqual(lst1, lst2)
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
Person.objects.prefetch_related(Prefetch('houses', to_attr='houses_lst'), 'houses_lst__rooms'),
[['houses_lst', 'rooms']]
)
self.assertEqual(lst1, lst2)
with self.assertNumQueries(3):
lst2 = self.traverse_qs(
Person.objects.prefetch_related(
Prefetch('houses', to_attr='houses_lst'),
Prefetch('houses_lst__rooms', to_attr='rooms_lst')
),
[['houses_lst', 'rooms_lst']]
)
self.assertEqual(lst1, lst2)
def test_generic_rel(self):
bookmark = Bookmark.objects.create(url='http://www.djangoproject.com/')
TaggedItem.objects.create(content_object=bookmark, tag='django')
TaggedItem.objects.create(content_object=bookmark, favorite=bookmark, tag='python')
# Control lookups.
with self.assertNumQueries(4):
lst1 = self.traverse_qs(
Bookmark.objects.prefetch_related('tags', 'tags__content_object', 'favorite_tags'),
[['tags', 'content_object'], ['favorite_tags']]
)
# Test lookups.
with self.assertNumQueries(4):
lst2 = self.traverse_qs(
Bookmark.objects.prefetch_related(
Prefetch('tags', to_attr='tags_lst'),
Prefetch('tags_lst__content_object'),
Prefetch('favorite_tags'),
),
[['tags_lst', 'content_object'], ['favorite_tags']]
)
self.assertEqual(lst1, lst2)
def test_custom_qs(self):
# Test basic.
with self.assertNumQueries(2):
lst1 = list(Person.objects.prefetch_related('houses'))
with self.assertNumQueries(2):
lst2 = list(Person.objects.prefetch_related(
Prefetch('houses', queryset=House.objects.all(), to_attr='houses_lst')))
self.assertEqual(
self.traverse_qs(lst1, [['houses']]),
self.traverse_qs(lst2, [['houses_lst']])
)
# Test queryset filtering.
with self.assertNumQueries(2):
lst2 = list(Person.objects.prefetch_related(
Prefetch('houses', queryset=House.objects.filter(pk__in=[self.house1.pk, self.house3.pk]), to_attr='houses_lst')))
self.assertEqual(len(lst2[0].houses_lst), 1)
self.assertEqual(lst2[0].houses_lst[0], self.house1)
self.assertEqual(len(lst2[1].houses_lst), 1)
self.assertEqual(lst2[1].houses_lst[0], self.house3)
# Test flattened.
with self.assertNumQueries(3):
lst1 = list(Person.objects.prefetch_related('houses__rooms'))
with self.assertNumQueries(3):
lst2 = list(Person.objects.prefetch_related(
Prefetch('houses__rooms', queryset=Room.objects.all(), to_attr='rooms_lst')))
self.assertEqual(
self.traverse_qs(lst1, [['houses', 'rooms']]),
self.traverse_qs(lst2, [['houses', 'rooms_lst']])
)
# Test inner select_related.
with self.assertNumQueries(3):
lst1 = list(Person.objects.prefetch_related('houses__owner'))
with self.assertNumQueries(2):
lst2 = list(Person.objects.prefetch_related(
Prefetch('houses', queryset=House.objects.select_related('owner'))))
self.assertEqual(
self.traverse_qs(lst1, [['houses', 'owner']]),
self.traverse_qs(lst2, [['houses', 'owner']])
)
# Test inner prefetch.
inner_rooms_qs = Room.objects.filter(pk__in=[self.room1_1.pk, self.room1_2.pk])
houses_qs_prf = House.objects.prefetch_related(
Prefetch('rooms', queryset=inner_rooms_qs, to_attr='rooms_lst'))
with self.assertNumQueries(3):
lst2 = list(Person.objects.prefetch_related(
Prefetch('houses', queryset=houses_qs_prf.filter(pk=self.house1.pk), to_attr='houses_lst')))
self.assertEqual(len(lst2[0].houses_lst[0].rooms_lst), 2)
self.assertEqual(lst2[0].houses_lst[0].rooms_lst[0], self.room1_1)
self.assertEqual(lst2[0].houses_lst[0].rooms_lst[1], self.room1_2)
self.assertEqual(len(lst2[1].houses_lst), 0)
class DefaultManagerTests(TestCase):
def setUp(self):
@ -627,6 +912,45 @@ class MultiDbTests(TestCase):
self.assertEqual(ages, "50, 49")
def test_using_is_honored_custom_qs(self):
B = Book.objects.using('other')
A = Author.objects.using('other')
book1 = B.create(title="Poems")
book2 = B.create(title="Sense and Sensibility")
A.create(name="Charlotte Bronte", first_book=book1)
A.create(name="Jane Austen", first_book=book2)
# Implicit hinting
with self.assertNumQueries(2, using='other'):
prefetch = Prefetch('first_time_authors', queryset=Author.objects.all())
books = "".join("%s (%s)\n" %
(b.title, ", ".join(a.name for a in b.first_time_authors.all()))
for b in B.prefetch_related(prefetch))
self.assertEqual(books,
"Poems (Charlotte Bronte)\n"
"Sense and Sensibility (Jane Austen)\n")
# Explicit using on the same db.
with self.assertNumQueries(2, using='other'):
prefetch = Prefetch('first_time_authors', queryset=Author.objects.using('other'))
books = "".join("%s (%s)\n" %
(b.title, ", ".join(a.name for a in b.first_time_authors.all()))
for b in B.prefetch_related(prefetch))
self.assertEqual(books,
"Poems (Charlotte Bronte)\n"
"Sense and Sensibility (Jane Austen)\n")
# Explicit using on a different db.
with self.assertNumQueries(1, using='default'), self.assertNumQueries(1, using='other'):
prefetch = Prefetch('first_time_authors', queryset=Author.objects.using('default'))
books = "".join("%s (%s)\n" %
(b.title, ", ".join(a.name for a in b.first_time_authors.all()))
for b in B.prefetch_related(prefetch))
self.assertEqual(books,
"Poems ()\n"
"Sense and Sensibility ()\n")
class Ticket19607Tests(TestCase):