from __future__ import unicode_literals import warnings from django.contrib.contenttypes.models import ContentType from django.core.exceptions import ObjectDoesNotExist from django.db import connection from django.db.models import Prefetch, QuerySet from django.db.models.query import get_prefetcher from django.test import TestCase, override_settings from django.test.utils import CaptureQueriesContext from django.utils import six from django.utils.encoding import force_text from .models import ( Author, Author2, AuthorAddress, AuthorWithAge, Bio, Book, Bookmark, BookReview, BookWithYear, Comment, Department, Employee, FavoriteAuthors, House, LessonEntry, Person, Qualification, Reader, Room, TaggedItem, Teacher, WordEntry, ) class PrefetchRelatedTests(TestCase): @classmethod def setUpTestData(cls): cls.book1 = Book.objects.create(title='Poems') cls.book2 = Book.objects.create(title='Jane Eyre') cls.book3 = Book.objects.create(title='Wuthering Heights') cls.book4 = Book.objects.create(title='Sense and Sensibility') cls.author1 = Author.objects.create(name='Charlotte', first_book=cls.book1) cls.author2 = Author.objects.create(name='Anne', first_book=cls.book1) cls.author3 = Author.objects.create(name='Emily', first_book=cls.book1) cls.author4 = Author.objects.create(name='Jane', first_book=cls.book4) cls.book1.authors.add(cls.author1, cls.author2, cls.author3) cls.book2.authors.add(cls.author1) cls.book3.authors.add(cls.author3) cls.book4.authors.add(cls.author4) cls.reader1 = Reader.objects.create(name='Amy') cls.reader2 = Reader.objects.create(name='Belinda') cls.reader1.books_read.add(cls.book1, cls.book4) cls.reader2.books_read.add(cls.book2, cls.book4) def test_m2m_forward(self): with self.assertNumQueries(2): lists = [list(b.authors.all()) for b in Book.objects.prefetch_related('authors')] normal_lists = [list(b.authors.all()) for b in Book.objects.all()] self.assertEqual(lists, normal_lists) def test_m2m_reverse(self): with self.assertNumQueries(2): lists = [list(a.books.all()) for a in Author.objects.prefetch_related('books')] normal_lists = [list(a.books.all()) for a in Author.objects.all()] self.assertEqual(lists, normal_lists) def test_foreignkey_forward(self): with self.assertNumQueries(2): books = [a.first_book for a in Author.objects.prefetch_related('first_book')] normal_books = [a.first_book for a in Author.objects.all()] self.assertEqual(books, normal_books) def test_foreignkey_reverse(self): with self.assertNumQueries(2): [list(b.first_time_authors.all()) for b in Book.objects.prefetch_related('first_time_authors')] self.assertQuerysetEqual(self.book2.authors.all(), [""]) def test_onetoone_reverse_no_match(self): # Regression for #17439 with self.assertNumQueries(2): book = Book.objects.prefetch_related('bookwithyear').all()[0] with self.assertNumQueries(0): with self.assertRaises(BookWithYear.DoesNotExist): book.bookwithyear def test_survives_clone(self): with self.assertNumQueries(2): [list(b.first_time_authors.all()) for b in Book.objects.prefetch_related('first_time_authors').exclude(id=1000)] def test_len(self): with self.assertNumQueries(2): qs = Book.objects.prefetch_related('first_time_authors') len(qs) [list(b.first_time_authors.all()) for b in qs] def test_bool(self): with self.assertNumQueries(2): qs = Book.objects.prefetch_related('first_time_authors') bool(qs) [list(b.first_time_authors.all()) for b in qs] def test_count(self): with self.assertNumQueries(2): qs = Book.objects.prefetch_related('first_time_authors') [b.first_time_authors.count() for b in qs] def test_exists(self): with self.assertNumQueries(2): qs = Book.objects.prefetch_related('first_time_authors') [b.first_time_authors.exists() for b in qs] def test_in_and_prefetch_related(self): """ Regression test for #20242 - QuerySet "in" didn't work the first time when using prefetch_related. This was fixed by the removal of chunked reads from QuerySet iteration in 70679243d1786e03557c28929f9762a119e3ac14. """ qs = Book.objects.prefetch_related('first_time_authors') self.assertIn(qs[0], qs) def test_clear(self): """ Test that we can clear the behavior by calling prefetch_related() """ with self.assertNumQueries(5): with_prefetch = Author.objects.prefetch_related('books') without_prefetch = with_prefetch.prefetch_related(None) [list(a.books.all()) for a in without_prefetch] def test_m2m_then_m2m(self): """ Test we can follow a m2m and another m2m """ with self.assertNumQueries(3): qs = Author.objects.prefetch_related('books__read_by') lists = [[[six.text_type(r) for r in b.read_by.all()] for b in a.books.all()] for a in qs] self.assertEqual(lists, [ [["Amy"], ["Belinda"]], # Charlotte - Poems, Jane Eyre [["Amy"]], # Anne - Poems [["Amy"], []], # Emily - Poems, Wuthering Heights [["Amy", "Belinda"]], # Jane - Sense and Sense ]) def test_overriding_prefetch(self): with self.assertNumQueries(3): qs = Author.objects.prefetch_related('books', 'books__read_by') lists = [[[six.text_type(r) for r in b.read_by.all()] for b in a.books.all()] for a in qs] self.assertEqual(lists, [ [["Amy"], ["Belinda"]], # Charlotte - Poems, Jane Eyre [["Amy"]], # Anne - Poems [["Amy"], []], # Emily - Poems, Wuthering Heights [["Amy", "Belinda"]], # Jane - Sense and Sense ]) with self.assertNumQueries(3): qs = Author.objects.prefetch_related('books__read_by', 'books') lists = [[[six.text_type(r) for r in b.read_by.all()] for b in a.books.all()] for a in qs] self.assertEqual(lists, [ [["Amy"], ["Belinda"]], # Charlotte - Poems, Jane Eyre [["Amy"]], # Anne - Poems [["Amy"], []], # Emily - Poems, Wuthering Heights [["Amy", "Belinda"]], # Jane - Sense and Sense ]) def test_get(self): """ Test that objects retrieved with .get() get the prefetch behavior. """ # Need a double with self.assertNumQueries(3): author = Author.objects.prefetch_related('books__read_by').get(name="Charlotte") lists = [[six.text_type(r) for r in b.read_by.all()] for b in author.books.all()] self.assertEqual(lists, [["Amy"], ["Belinda"]]) # Poems, Jane Eyre def test_foreign_key_then_m2m(self): """ Test we can follow an m2m relation after a relation like ForeignKey that doesn't have many objects """ with self.assertNumQueries(2): qs = Author.objects.select_related('first_book').prefetch_related('first_book__read_by') lists = [[six.text_type(r) for r in a.first_book.read_by.all()] for a in qs] self.assertEqual(lists, [["Amy"], ["Amy"], ["Amy"], ["Amy", "Belinda"]]) def test_reverse_one_to_one_then_m2m(self): """ Test that we can follow a m2m relation after going through the select_related reverse of an o2o. """ qs = Author.objects.prefetch_related('bio__books').select_related('bio') with self.assertNumQueries(1): list(qs.all()) Bio.objects.create(author=self.author1) with self.assertNumQueries(2): list(qs.all()) def test_attribute_error(self): qs = Reader.objects.all().prefetch_related('books_read__xyz') with self.assertRaises(AttributeError) as cm: list(qs) self.assertIn('prefetch_related', str(cm.exception)) def test_invalid_final_lookup(self): qs = Book.objects.prefetch_related('authors__name') with self.assertRaises(ValueError) as cm: list(qs) self.assertIn('prefetch_related', str(cm.exception)) self.assertIn("name", str(cm.exception)) def test_forward_m2m_to_attr_conflict(self): msg = 'to_attr=authors conflicts with a field on the Book model.' authors = Author.objects.all() with self.assertRaisesMessage(ValueError, msg): list(Book.objects.prefetch_related( Prefetch('authors', queryset=authors, to_attr='authors'), )) # Without the ValueError, an author was deleted due to the implicit # save of the relation assignment. self.assertEqual(self.book1.authors.count(), 3) def test_reverse_m2m_to_attr_conflict(self): msg = 'to_attr=books conflicts with a field on the Author model.' poems = Book.objects.filter(title='Poems') with self.assertRaisesMessage(ValueError, msg): list(Author.objects.prefetch_related( Prefetch('books', queryset=poems, to_attr='books'), )) # Without the ValueError, a book was deleted due to the implicit # save of reverse relation assignment. self.assertEqual(self.author1.books.count(), 2) def test_m2m_then_reverse_fk_object_ids(self): with CaptureQueriesContext(connection) as queries: list(Book.objects.prefetch_related('authors__addresses')) sql = queries[-1]['sql'] self.assertEqual(sql.count(self.author1.name), 1) def test_m2m_then_m2m_object_ids(self): with CaptureQueriesContext(connection) as queries: list(Book.objects.prefetch_related('authors__favorite_authors')) sql = queries[-1]['sql'] self.assertEqual(sql.count(self.author1.name), 1) def test_m2m_then_reverse_one_to_one_object_ids(self): with CaptureQueriesContext(connection) as queries: list(Book.objects.prefetch_related('authors__authorwithage')) sql = queries[-1]['sql'] self.assertEqual(sql.count(str(self.author1.id)), 1, sql) 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 try: related = getattr(obj, part[0]) except ObjectDoesNotExist: continue if related is not None: rel_objs.extend(cls.traverse_qs(related, [part[1:]])) ret_val.append((obj, rel_objs)) return ret_val @classmethod def setUpTestData(cls): cls.person1 = Person.objects.create(name='Joe') cls.person2 = Person.objects.create(name='Mary') # Set main_room for each house before creating the next one for # databases where supports_nullable_unique_constraints is False. cls.house1 = House.objects.create(name='House 1', address='123 Main St', owner=cls.person1) cls.room1_1 = Room.objects.create(name='Dining room', house=cls.house1) cls.room1_2 = Room.objects.create(name='Lounge', house=cls.house1) cls.room1_3 = Room.objects.create(name='Kitchen', house=cls.house1) cls.house1.main_room = cls.room1_1 cls.house1.save() cls.person1.houses.add(cls.house1) cls.house2 = House.objects.create(name='House 2', address='45 Side St', owner=cls.person1) cls.room2_1 = Room.objects.create(name='Dining room', house=cls.house2) cls.room2_2 = Room.objects.create(name='Lounge', house=cls.house2) cls.room2_3 = Room.objects.create(name='Kitchen', house=cls.house2) cls.house2.main_room = cls.room2_1 cls.house2.save() cls.person1.houses.add(cls.house2) cls.house3 = House.objects.create(name='House 3', address='6 Downing St', owner=cls.person2) cls.room3_1 = Room.objects.create(name='Dining room', house=cls.house3) cls.room3_2 = Room.objects.create(name='Lounge', house=cls.house3) cls.room3_3 = Room.objects.create(name='Kitchen', house=cls.house3) cls.house3.main_room = cls.room3_1 cls.house3.save() cls.person2.houses.add(cls.house3) cls.house4 = House.objects.create(name='house 4', address="7 Regents St", owner=cls.person2) cls.room4_1 = Room.objects.create(name='Dining room', house=cls.house4) cls.room4_2 = Room.objects.create(name='Lounge', house=cls.house4) cls.room4_3 = Room.objects.create(name='Kitchen', house=cls.house4) cls.house4.main_room = cls.room4_1 cls.house4.save() cls.person2.houses.add(cls.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: Lookup was already seen with a different queryset. with self.assertRaises(ValueError): self.traverse_qs( Person.objects.prefetch_related('houses__rooms', Prefetch('houses', queryset=House.objects.all())), [['houses', 'rooms']] ) # Ambiguous: Lookup houses_lst doesn't yet exist when performing houses_lst__rooms. with self.assertRaises(AttributeError): self.traverse_qs( Person.objects.prefetch_related( 'houses_lst__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_traverse_single_item_property(self): # Control lookups. with self.assertNumQueries(5): lst1 = self.traverse_qs( Person.objects.prefetch_related( 'houses__rooms', 'primary_house__occupants__houses', ), [['primary_house', 'occupants', 'houses']] ) # Test lookups. with self.assertNumQueries(5): lst2 = self.traverse_qs( Person.objects.prefetch_related( 'houses__rooms', Prefetch('primary_house__occupants', to_attr='occupants_lst'), 'primary_house__occupants_lst__houses', ), [['primary_house', 'occupants_lst', 'houses']] ) self.assertEqual(lst1, lst2) def test_traverse_multiple_items_property(self): # Control lookups. with self.assertNumQueries(4): lst1 = self.traverse_qs( Person.objects.prefetch_related( 'houses', 'all_houses__occupants__houses', ), [['all_houses', 'occupants', 'houses']] ) # Test lookups. with self.assertNumQueries(4): lst2 = self.traverse_qs( Person.objects.prefetch_related( 'houses', Prefetch('all_houses__occupants', to_attr='occupants_lst'), 'all_houses__occupants_lst__houses', ), [['all_houses', 'occupants_lst', 'houses']] ) 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(4): lst2 = list(Person.objects.prefetch_related( Prefetch('houses', queryset=houses_qs_prf.filter(pk=self.house1.pk), to_attr='houses_lst'), Prefetch('houses_lst__rooms_lst__main_room_of') )) 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(lst2[0].houses_lst[0].rooms_lst[0].main_room_of, self.house1) self.assertEqual(len(lst2[1].houses_lst), 0) # Test ForwardManyToOneDescriptor. houses = House.objects.select_related('owner') with self.assertNumQueries(6): rooms = Room.objects.all().prefetch_related('house') lst1 = self.traverse_qs(rooms, [['house', 'owner']]) with self.assertNumQueries(2): rooms = Room.objects.all().prefetch_related(Prefetch('house', queryset=houses.all())) lst2 = self.traverse_qs(rooms, [['house', 'owner']]) self.assertEqual(lst1, lst2) with self.assertNumQueries(2): houses = House.objects.select_related('owner') rooms = Room.objects.all().prefetch_related(Prefetch('house', queryset=houses.all(), to_attr='house_attr')) lst2 = self.traverse_qs(rooms, [['house_attr', 'owner']]) self.assertEqual(lst1, lst2) room = Room.objects.all().prefetch_related( Prefetch('house', queryset=houses.filter(address='DoesNotExist')) ).first() with self.assertRaises(ObjectDoesNotExist): getattr(room, 'house') room = Room.objects.all().prefetch_related( Prefetch('house', queryset=houses.filter(address='DoesNotExist'), to_attr='house_attr') ).first() self.assertIsNone(room.house_attr) rooms = Room.objects.all().prefetch_related(Prefetch('house', queryset=House.objects.only('name'))) with self.assertNumQueries(2): getattr(rooms.first().house, 'name') with self.assertNumQueries(3): getattr(rooms.first().house, 'address') # Test ReverseOneToOneDescriptor. houses = House.objects.select_related('owner') with self.assertNumQueries(6): rooms = Room.objects.all().prefetch_related('main_room_of') lst1 = self.traverse_qs(rooms, [['main_room_of', 'owner']]) with self.assertNumQueries(2): rooms = Room.objects.all().prefetch_related(Prefetch('main_room_of', queryset=houses.all())) lst2 = self.traverse_qs(rooms, [['main_room_of', 'owner']]) self.assertEqual(lst1, lst2) with self.assertNumQueries(2): rooms = list( Room.objects.all().prefetch_related( Prefetch('main_room_of', queryset=houses.all(), to_attr='main_room_of_attr') ) ) lst2 = self.traverse_qs(rooms, [['main_room_of_attr', 'owner']]) self.assertEqual(lst1, lst2) room = Room.objects.filter(main_room_of__isnull=False).prefetch_related( Prefetch('main_room_of', queryset=houses.filter(address='DoesNotExist')) ).first() with self.assertRaises(ObjectDoesNotExist): getattr(room, 'main_room_of') room = Room.objects.filter(main_room_of__isnull=False).prefetch_related( Prefetch('main_room_of', queryset=houses.filter(address='DoesNotExist'), to_attr='main_room_of_attr') ).first() self.assertIsNone(room.main_room_of_attr) # The custom queryset filters should be applied to the queryset # instance returned by the manager. person = Person.objects.prefetch_related( Prefetch('houses', queryset=House.objects.filter(name='House 1')), ).get(pk=self.person1.pk) self.assertEqual( list(person.houses.all()), list(person.houses.all().all()), ) def test_nested_prefetch_related_are_not_overwritten(self): # Regression test for #24873 houses_2 = House.objects.prefetch_related(Prefetch('rooms')) persons = Person.objects.prefetch_related(Prefetch('houses', queryset=houses_2)) houses = House.objects.prefetch_related(Prefetch('occupants', queryset=persons)) list(houses) # queryset must be evaluated once to reproduce the bug. self.assertEqual( houses.all()[0].occupants.all()[0].houses.all()[1].rooms.all()[0], self.room2_1 ) def test_apply_rel_filters_deprecation_shim(self): # Simulate a missing `_apply_rel_filters` method. del Person.houses.related_manager_cls._apply_rel_filters # Also remove `get_queryset` as it rely on `_apply_rel_filters`. del Person.houses.related_manager_cls.get_queryset try: with warnings.catch_warnings(record=True) as warns: warnings.simplefilter('always') list(Person.objects.prefetch_related( Prefetch('houses', queryset=House.objects.filter(name='House 1')) )) finally: # Deleting `related_manager_cls` will force the creation of a new # class since it's a `cached_property`. del Person.houses.related_manager_cls msg = ( 'The `django.db.models.fields.related_descriptors.ManyRelatedManager` class ' 'must implement a `_apply_rel_filters()` method that accepts a `QuerySet` as ' 'its single argument and returns an appropriately filtered version of it.' ) self.assertEqual(len(warns), 2) # Once person. self.assertEqual(str(warns[0].message), msg) self.assertEqual(str(warns[0].message), msg) def test_values_queryset(self): with self.assertRaisesMessage(ValueError, 'Prefetch querysets cannot use values().'): Prefetch('houses', House.objects.values('pk')) def test_to_attr_doesnt_cache_through_attr_as_list(self): house = House.objects.prefetch_related( Prefetch('rooms', queryset=Room.objects.all(), to_attr='to_rooms'), ).get(pk=self.house3.pk) self.assertIsInstance(house.rooms.all(), QuerySet) def test_to_attr_cached_property(self): persons = Person.objects.prefetch_related( Prefetch('houses', House.objects.all(), to_attr='cached_all_houses'), ) for person in persons: # To bypass caching at the related descriptor level, don't use # person.houses.all() here. all_houses = list(House.objects.filter(occupants=person)) with self.assertNumQueries(0): self.assertEqual(person.cached_all_houses, all_houses) class DefaultManagerTests(TestCase): def setUp(self): self.qual1 = Qualification.objects.create(name="BA") self.qual2 = Qualification.objects.create(name="BSci") self.qual3 = Qualification.objects.create(name="MA") self.qual4 = Qualification.objects.create(name="PhD") self.teacher1 = Teacher.objects.create(name="Mr Cleese") self.teacher2 = Teacher.objects.create(name="Mr Idle") self.teacher3 = Teacher.objects.create(name="Mr Chapman") self.teacher1.qualifications.add(self.qual1, self.qual2, self.qual3, self.qual4) self.teacher2.qualifications.add(self.qual1) self.teacher3.qualifications.add(self.qual2) self.dept1 = Department.objects.create(name="English") self.dept2 = Department.objects.create(name="Physics") self.dept1.teachers.add(self.teacher1, self.teacher2) self.dept2.teachers.add(self.teacher1, self.teacher3) def test_m2m_then_m2m(self): with self.assertNumQueries(3): # When we prefetch the teachers, and force the query, we don't want # the default manager on teachers to immediately get all the related # qualifications, since this will do one query per teacher. qs = Department.objects.prefetch_related('teachers') depts = "".join("%s department: %s\n" % (dept.name, ", ".join(six.text_type(t) for t in dept.teachers.all())) for dept in qs) self.assertEqual(depts, "English department: Mr Cleese (BA, BSci, MA, PhD), Mr Idle (BA)\n" "Physics department: Mr Cleese (BA, BSci, MA, PhD), Mr Chapman (BSci)\n") class GenericRelationTests(TestCase): @classmethod def setUpTestData(cls): book1 = Book.objects.create(title="Winnie the Pooh") book2 = Book.objects.create(title="Do you like green eggs and spam?") book3 = Book.objects.create(title="Three Men In A Boat") reader1 = Reader.objects.create(name="me") reader2 = Reader.objects.create(name="you") reader3 = Reader.objects.create(name="someone") book1.read_by.add(reader1, reader2) book2.read_by.add(reader2) book3.read_by.add(reader3) cls.book1, cls.book2, cls.book3 = book1, book2, book3 cls.reader1, cls.reader2, cls.reader3 = reader1, reader2, reader3 def test_prefetch_GFK(self): TaggedItem.objects.create(tag="awesome", content_object=self.book1) TaggedItem.objects.create(tag="great", content_object=self.reader1) TaggedItem.objects.create(tag="outstanding", content_object=self.book2) TaggedItem.objects.create(tag="amazing", content_object=self.reader3) # 1 for TaggedItem table, 1 for Book table, 1 for Reader table with self.assertNumQueries(3): qs = TaggedItem.objects.prefetch_related('content_object') list(qs) def test_prefetch_GFK_nonint_pk(self): Comment.objects.create(comment="awesome", content_object=self.book1) # 1 for Comment table, 1 for Book table with self.assertNumQueries(2): qs = Comment.objects.prefetch_related('content_object') [c.content_object for c in qs] def test_traverse_GFK(self): """ Test that we can traverse a 'content_object' with prefetch_related() and get to related objects on the other side (assuming it is suitably filtered) """ TaggedItem.objects.create(tag="awesome", content_object=self.book1) TaggedItem.objects.create(tag="awesome", content_object=self.book2) TaggedItem.objects.create(tag="awesome", content_object=self.book3) TaggedItem.objects.create(tag="awesome", content_object=self.reader1) TaggedItem.objects.create(tag="awesome", content_object=self.reader2) ct = ContentType.objects.get_for_model(Book) # We get 3 queries - 1 for main query, 1 for content_objects since they # all use the same table, and 1 for the 'read_by' relation. with self.assertNumQueries(3): # If we limit to books, we know that they will have 'read_by' # attributes, so the following makes sense: qs = TaggedItem.objects.filter(content_type=ct, tag='awesome').prefetch_related('content_object__read_by') readers_of_awesome_books = {r.name for tag in qs for r in tag.content_object.read_by.all()} self.assertEqual(readers_of_awesome_books, {"me", "you", "someone"}) def test_nullable_GFK(self): TaggedItem.objects.create(tag="awesome", content_object=self.book1, created_by=self.reader1) TaggedItem.objects.create(tag="great", content_object=self.book2) TaggedItem.objects.create(tag="rubbish", content_object=self.book3) with self.assertNumQueries(2): result = [t.created_by for t in TaggedItem.objects.prefetch_related('created_by')] self.assertEqual(result, [t.created_by for t in TaggedItem.objects.all()]) def test_generic_relation(self): bookmark = Bookmark.objects.create(url='http://www.djangoproject.com/') TaggedItem.objects.create(content_object=bookmark, tag='django') TaggedItem.objects.create(content_object=bookmark, tag='python') with self.assertNumQueries(2): tags = [t.tag for b in Bookmark.objects.prefetch_related('tags') for t in b.tags.all()] self.assertEqual(sorted(tags), ["django", "python"]) def test_charfield_GFK(self): b = Bookmark.objects.create(url='http://www.djangoproject.com/') TaggedItem.objects.create(content_object=b, tag='django') TaggedItem.objects.create(content_object=b, favorite=b, tag='python') with self.assertNumQueries(3): bookmark = Bookmark.objects.filter(pk=b.pk).prefetch_related('tags', 'favorite_tags')[0] self.assertEqual(sorted([i.tag for i in bookmark.tags.all()]), ["django", "python"]) self.assertEqual([i.tag for i in bookmark.favorite_tags.all()], ["python"]) def test_custom_queryset(self): bookmark = Bookmark.objects.create(url='http://www.djangoproject.com/') django_tag = TaggedItem.objects.create(content_object=bookmark, tag='django') TaggedItem.objects.create(content_object=bookmark, tag='python') with self.assertNumQueries(2): bookmark = Bookmark.objects.prefetch_related( Prefetch('tags', TaggedItem.objects.filter(tag='django')), ).get() with self.assertNumQueries(0): self.assertEqual(list(bookmark.tags.all()), [django_tag]) # The custom queryset filters should be applied to the queryset # instance returned by the manager. self.assertEqual(list(bookmark.tags.all()), list(bookmark.tags.all().all())) class MultiTableInheritanceTest(TestCase): @classmethod def setUpTestData(cls): cls.book1 = BookWithYear.objects.create(title='Poems', published_year=2010) cls.book2 = BookWithYear.objects.create(title='More poems', published_year=2011) cls.author1 = AuthorWithAge.objects.create(name='Jane', first_book=cls.book1, age=50) cls.author2 = AuthorWithAge.objects.create(name='Tom', first_book=cls.book1, age=49) cls.author3 = AuthorWithAge.objects.create(name='Robert', first_book=cls.book2, age=48) cls.author_address = AuthorAddress.objects.create(author=cls.author1, address='SomeStreet 1') cls.book2.aged_authors.add(cls.author2, cls.author3) cls.br1 = BookReview.objects.create(book=cls.book1, notes='review book1') cls.br2 = BookReview.objects.create(book=cls.book2, notes='review book2') def test_foreignkey(self): with self.assertNumQueries(2): qs = AuthorWithAge.objects.prefetch_related('addresses') addresses = [[six.text_type(address) for address in obj.addresses.all()] for obj in qs] self.assertEqual(addresses, [[six.text_type(self.author_address)], [], []]) def test_foreignkey_to_inherited(self): with self.assertNumQueries(2): qs = BookReview.objects.prefetch_related('book') titles = [obj.book.title for obj in qs] self.assertEqual(titles, ["Poems", "More poems"]) def test_m2m_to_inheriting_model(self): qs = AuthorWithAge.objects.prefetch_related('books_with_year') with self.assertNumQueries(2): lst = [[six.text_type(book) for book in author.books_with_year.all()] for author in qs] qs = AuthorWithAge.objects.all() lst2 = [[six.text_type(book) for book in author.books_with_year.all()] for author in qs] self.assertEqual(lst, lst2) qs = BookWithYear.objects.prefetch_related('aged_authors') with self.assertNumQueries(2): lst = [[six.text_type(author) for author in book.aged_authors.all()] for book in qs] qs = BookWithYear.objects.all() lst2 = [[six.text_type(author) for author in book.aged_authors.all()] for book in qs] self.assertEqual(lst, lst2) def test_parent_link_prefetch(self): with self.assertNumQueries(2): [a.author for a in AuthorWithAge.objects.prefetch_related('author')] @override_settings(DEBUG=True) def test_child_link_prefetch(self): with self.assertNumQueries(2): l = [a.authorwithage for a in Author.objects.prefetch_related('authorwithage')] # Regression for #18090: the prefetching query must include an IN clause. # Note that on Oracle the table name is upper case in the generated SQL, # thus the .lower() call. self.assertIn('authorwithage', connection.queries[-1]['sql'].lower()) self.assertIn(' IN ', connection.queries[-1]['sql']) self.assertEqual(l, [a.authorwithage for a in Author.objects.all()]) class ForeignKeyToFieldTest(TestCase): @classmethod def setUpTestData(cls): cls.book = Book.objects.create(title='Poems') cls.author1 = Author.objects.create(name='Jane', first_book=cls.book) cls.author2 = Author.objects.create(name='Tom', first_book=cls.book) cls.author3 = Author.objects.create(name='Robert', first_book=cls.book) cls.author_address = AuthorAddress.objects.create(author=cls.author1, address='SomeStreet 1') FavoriteAuthors.objects.create(author=cls.author1, likes_author=cls.author2) FavoriteAuthors.objects.create(author=cls.author2, likes_author=cls.author3) FavoriteAuthors.objects.create(author=cls.author3, likes_author=cls.author1) def test_foreignkey(self): with self.assertNumQueries(2): qs = Author.objects.prefetch_related('addresses') addresses = [[six.text_type(address) for address in obj.addresses.all()] for obj in qs] self.assertEqual(addresses, [[six.text_type(self.author_address)], [], []]) def test_m2m(self): with self.assertNumQueries(3): qs = Author.objects.all().prefetch_related('favorite_authors', 'favors_me') favorites = [( [six.text_type(i_like) for i_like in author.favorite_authors.all()], [six.text_type(likes_me) for likes_me in author.favors_me.all()] ) for author in qs] self.assertEqual( favorites, [ ([six.text_type(self.author2)], [six.text_type(self.author3)]), ([six.text_type(self.author3)], [six.text_type(self.author1)]), ([six.text_type(self.author1)], [six.text_type(self.author2)]) ] ) class LookupOrderingTest(TestCase): """ Test cases that demonstrate that ordering of lookups is important, and ensure it is preserved. """ def setUp(self): self.person1 = Person.objects.create(name="Joe") self.person2 = Person.objects.create(name="Mary") # Set main_room for each house before creating the next one for # databases where supports_nullable_unique_constraints is False. self.house1 = House.objects.create(address="123 Main St") 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.house1.main_room = self.room1_1 self.house1.save() self.person1.houses.add(self.house1) self.house2 = House.objects.create(address="45 Side St") self.room2_1 = Room.objects.create(name="Dining room", house=self.house2) self.room2_2 = Room.objects.create(name="Lounge", house=self.house2) self.house2.main_room = self.room2_1 self.house2.save() self.person1.houses.add(self.house2) self.house3 = House.objects.create(address="6 Downing St") 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.house3.main_room = self.room3_1 self.house3.save() self.person2.houses.add(self.house3) self.house4 = House.objects.create(address="7 Regents St") self.room4_1 = Room.objects.create(name="Dining room", house=self.house4) self.room4_2 = Room.objects.create(name="Lounge", house=self.house4) self.house4.main_room = self.room4_1 self.house4.save() self.person2.houses.add(self.house4) def test_order(self): with self.assertNumQueries(4): # The following two queries must be done in the same order as written, # otherwise 'primary_house' will cause non-prefetched lookups qs = Person.objects.prefetch_related('houses__rooms', 'primary_house__occupants') [list(p.primary_house.occupants.all()) for p in qs] class NullableTest(TestCase): @classmethod def setUpTestData(cls): boss = Employee.objects.create(name="Peter") Employee.objects.create(name="Joe", boss=boss) Employee.objects.create(name="Angela", boss=boss) def test_traverse_nullable(self): # Because we use select_related() for 'boss', it doesn't need to be # prefetched, but we can still traverse it although it contains some nulls with self.assertNumQueries(2): qs = Employee.objects.select_related('boss').prefetch_related('boss__serfs') co_serfs = [list(e.boss.serfs.all()) if e.boss is not None else [] for e in qs] qs2 = Employee.objects.select_related('boss') co_serfs2 = [list(e.boss.serfs.all()) if e.boss is not None else [] for e in qs2] self.assertEqual(co_serfs, co_serfs2) def test_prefetch_nullable(self): # One for main employee, one for boss, one for serfs with self.assertNumQueries(3): qs = Employee.objects.prefetch_related('boss__serfs') co_serfs = [list(e.boss.serfs.all()) if e.boss is not None else [] for e in qs] qs2 = Employee.objects.all() co_serfs2 = [list(e.boss.serfs.all()) if e.boss is not None else [] for e in qs2] self.assertEqual(co_serfs, co_serfs2) def test_in_bulk(self): """ In-bulk does correctly prefetch objects by not using .iterator() directly. """ boss1 = Employee.objects.create(name="Peter") boss2 = Employee.objects.create(name="Jack") with self.assertNumQueries(2): # Check that prefetch is done and it does not cause any errors. bulk = Employee.objects.prefetch_related('serfs').in_bulk([boss1.pk, boss2.pk]) for b in bulk.values(): list(b.serfs.all()) class MultiDbTests(TestCase): multi_db = True def test_using_is_honored_m2m(self): B = Book.objects.using('other') A = Author.objects.using('other') book1 = B.create(title="Poems") book2 = B.create(title="Jane Eyre") book3 = B.create(title="Wuthering Heights") book4 = B.create(title="Sense and Sensibility") author1 = A.create(name="Charlotte", first_book=book1) author2 = A.create(name="Anne", first_book=book1) author3 = A.create(name="Emily", first_book=book1) author4 = A.create(name="Jane", first_book=book4) book1.authors.add(author1, author2, author3) book2.authors.add(author1) book3.authors.add(author3) book4.authors.add(author4) # Forward qs1 = B.prefetch_related('authors') with self.assertNumQueries(2, using='other'): books = "".join("%s (%s)\n" % (book.title, ", ".join(a.name for a in book.authors.all())) for book in qs1) self.assertEqual(books, "Poems (Charlotte, Anne, Emily)\n" "Jane Eyre (Charlotte)\n" "Wuthering Heights (Emily)\n" "Sense and Sensibility (Jane)\n") # Reverse qs2 = A.prefetch_related('books') with self.assertNumQueries(2, using='other'): authors = "".join("%s: %s\n" % (author.name, ", ".join(b.title for b in author.books.all())) for author in qs2) self.assertEqual(authors, "Charlotte: Poems, Jane Eyre\n" "Anne: Poems\n" "Emily: Poems, Wuthering Heights\n" "Jane: Sense and Sensibility\n") def test_using_is_honored_fkey(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) # Forward with self.assertNumQueries(2, using='other'): books = ", ".join(a.first_book.title for a in A.prefetch_related('first_book')) self.assertEqual("Poems, Sense and Sensibility", books) # Reverse with self.assertNumQueries(2, 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('first_time_authors')) self.assertEqual(books, "Poems (Charlotte Bronte)\n" "Sense and Sensibility (Jane Austen)\n") def test_using_is_honored_inheritance(self): B = BookWithYear.objects.using('other') A = AuthorWithAge.objects.using('other') book1 = B.create(title="Poems", published_year=2010) B.create(title="More poems", published_year=2011) A.create(name='Jane', first_book=book1, age=50) A.create(name='Tom', first_book=book1, age=49) # parent link with self.assertNumQueries(2, using='other'): authors = ", ".join(a.author.name for a in A.prefetch_related('author')) self.assertEqual(authors, "Jane, Tom") # child link with self.assertNumQueries(2, using='other'): ages = ", ".join(str(a.authorwithage.age) for a in A.prefetch_related('authorwithage')) 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): def setUp(self): for id, name1, name2 in [ (1, 'einfach', 'simple'), (2, 'schwierig', 'difficult'), ]: LessonEntry.objects.create(id=id, name1=name1, name2=name2) for id, lesson_entry_id, name in [ (1, 1, 'einfach'), (2, 1, 'simple'), (3, 2, 'schwierig'), (4, 2, 'difficult'), ]: WordEntry.objects.create(id=id, lesson_entry_id=lesson_entry_id, name=name) def test_bug(self): list(WordEntry.objects.prefetch_related('lesson_entry', 'lesson_entry__wordentry_set')) class Ticket21410Tests(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") self.book4 = Book.objects.create(title="Sense and Sensibility") self.author1 = Author2.objects.create(name="Charlotte", first_book=self.book1) self.author2 = Author2.objects.create(name="Anne", first_book=self.book1) self.author3 = Author2.objects.create(name="Emily", first_book=self.book1) self.author4 = Author2.objects.create(name="Jane", first_book=self.book4) self.author1.favorite_books.add(self.book1, self.book2, self.book3) self.author2.favorite_books.add(self.book1) self.author3.favorite_books.add(self.book2) self.author4.favorite_books.add(self.book3) def test_bug(self): list(Author2.objects.prefetch_related('first_book', 'favorite_books')) class Ticket21760Tests(TestCase): def setUp(self): self.rooms = [] for _ in range(3): house = House.objects.create() for _ in range(3): self.rooms.append(Room.objects.create(house=house)) # Set main_room for each house before creating the next one for # databases where supports_nullable_unique_constraints is False. house.main_room = self.rooms[-3] house.save() def test_bug(self): prefetcher = get_prefetcher(self.rooms[0], 'house', 'house')[0] queryset = prefetcher.get_prefetch_queryset(list(Room.objects.all()))[0] self.assertNotIn(' JOIN ', force_text(queryset.query)) class Ticket25546Tests(TestCase): """ Nested prefetch_related() shouldn't trigger duplicate queries for the same lookup. Before, prefetch queries were for 'addresses', 'first_time_authors', and 'first_time_authors__addresses'. The last query is the duplicate. """ @classmethod def setUpTestData(cls): cls.book1, cls.book2 = [ Book.objects.create(title='book1'), Book.objects.create(title='book2'), ] cls.author11, cls.author12, cls.author21 = [ Author.objects.create(first_book=cls.book1, name='Author11'), Author.objects.create(first_book=cls.book1, name='Author12'), Author.objects.create(first_book=cls.book2, name='Author21'), ] cls.author1_address1, cls.author1_address2, cls.author2_address1 = [ AuthorAddress.objects.create(author=cls.author11, address='Happy place'), AuthorAddress.objects.create(author=cls.author12, address='Haunted house'), AuthorAddress.objects.create(author=cls.author21, address='Happy place'), ] def test_prefetch(self): with self.assertNumQueries(3): books = Book.objects.filter( title__in=['book1', 'book2'], ).prefetch_related( Prefetch( 'first_time_authors', Author.objects.prefetch_related( Prefetch( 'addresses', AuthorAddress.objects.filter(address='Happy place'), ) ), ), ) book1, book2 = list(books) with self.assertNumQueries(0): self.assertListEqual(list(book1.first_time_authors.all()), [self.author11, self.author12]) self.assertListEqual(list(book2.first_time_authors.all()), [self.author21]) self.assertListEqual(list(book1.first_time_authors.all()[0].addresses.all()), [self.author1_address1]) self.assertListEqual(list(book1.first_time_authors.all()[1].addresses.all()), []) self.assertListEqual(list(book2.first_time_authors.all()[0].addresses.all()), [self.author2_address1]) self.assertEqual( list(book1.first_time_authors.all()), list(book1.first_time_authors.all().all()) ) self.assertEqual( list(book2.first_time_authors.all()), list(book2.first_time_authors.all().all()) ) self.assertEqual( list(book1.first_time_authors.all()[0].addresses.all()), list(book1.first_time_authors.all()[0].addresses.all().all()) ) self.assertEqual( list(book1.first_time_authors.all()[1].addresses.all()), list(book1.first_time_authors.all()[1].addresses.all().all()) ) self.assertEqual( list(book2.first_time_authors.all()[0].addresses.all()), list(book2.first_time_authors.all()[0].addresses.all().all()) ) def test_prefetch_with_to_attr(self): with self.assertNumQueries(3): books = Book.objects.filter( title__in=['book1', 'book2'], ).prefetch_related( Prefetch( 'first_time_authors', Author.objects.prefetch_related( Prefetch( 'addresses', AuthorAddress.objects.filter(address='Happy place'), to_attr='happy_place', ) ), to_attr='first_authors', ), ) book1, book2 = list(books) with self.assertNumQueries(0): self.assertListEqual(book1.first_authors, [self.author11, self.author12]) self.assertListEqual(book2.first_authors, [self.author21]) self.assertListEqual(book1.first_authors[0].happy_place, [self.author1_address1]) self.assertListEqual(book1.first_authors[1].happy_place, []) self.assertListEqual(book2.first_authors[0].happy_place, [self.author2_address1])