Fixed #27554 -- Fixed prefetch_related() crash when fetching relations in nested Prefetches.
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@ -1423,10 +1423,15 @@ def prefetch_related_objects(model_instances, *related_lookups):
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# that we can continue with nullable or reverse relations.
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new_obj_list = []
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for obj in obj_list:
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try:
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new_obj = getattr(obj, through_attr)
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except exceptions.ObjectDoesNotExist:
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continue
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if through_attr in getattr(obj, '_prefetched_objects_cache', ()):
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# If related objects have been prefetched, use the
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# cache rather than the object's through_attr.
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new_obj = list(obj._prefetched_objects_cache.get(through_attr))
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else:
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try:
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new_obj = getattr(obj, through_attr)
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except exceptions.ObjectDoesNotExist:
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continue
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if new_obj is None:
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continue
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# We special-case `list` rather than something more generic
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@ -91,3 +91,6 @@ Bugfixes
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* Corrected the return type of ``ArrayField(CITextField())`` values retrieved
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from the database (:ticket:`28161`).
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* Fixed ``QuerySet.prefetch_related()`` crash when fetching relations in nested
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``Prefetch`` objects (:ticket:`27554`).
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@ -1361,3 +1361,37 @@ class Ticket25546Tests(TestCase):
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self.assertEqual(book1.first_authors[0].happy_place, [self.author1_address1])
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self.assertEqual(book1.first_authors[1].happy_place, [])
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self.assertEqual(book2.first_authors[0].happy_place, [self.author2_address1])
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class ReadPrefetchedObjectsCacheTests(TestCase):
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@classmethod
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def setUpTestData(cls):
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cls.book1 = Book.objects.create(title='Les confessions Volume I')
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cls.book2 = Book.objects.create(title='Candide')
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cls.author1 = AuthorWithAge.objects.create(name='Rousseau', first_book=cls.book1, age=70)
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cls.author2 = AuthorWithAge.objects.create(name='Voltaire', first_book=cls.book2, age=65)
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cls.book1.authors.add(cls.author1)
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cls.book2.authors.add(cls.author2)
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FavoriteAuthors.objects.create(author=cls.author1, likes_author=cls.author2)
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def test_retrieves_results_from_prefetched_objects_cache(self):
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"""
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When intermediary results are prefetched without a destination
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attribute, they are saved in the RelatedManager's cache
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(_prefetched_objects_cache). prefetch_related() uses this cache
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(#27554).
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"""
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authors = AuthorWithAge.objects.prefetch_related(
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Prefetch(
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'author',
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queryset=Author.objects.prefetch_related(
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# Results are saved in the RelatedManager's cache
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# (_prefetched_objects_cache) and do not replace the
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# RelatedManager on Author instances (favorite_authors)
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Prefetch('favorite_authors__first_book'),
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),
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),
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)
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with self.assertNumQueries(4):
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# AuthorWithAge -> Author -> FavoriteAuthors, Book
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self.assertQuerysetEqual(authors, ['<AuthorWithAge: Rousseau>', '<AuthorWithAge: Voltaire>'])
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