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Code Issues 25 Releases Wiki Activity

Fixed #25546 -- Prevented duplicate queries with nested prefetch_related().

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François Freitag 2016-01-10 17:54:57 +01:00 committed by Tim Graham
parent 13023ba867
commit bdbe50a491
2 changed files with 81 additions and 0 deletions
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2
django/db/models/query.py
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@ -1521,6 +1521,7 @@ def get_prefetcher(instance, attr):
rel_obj = getattr(instance, attr)
if hasattr(rel_obj, 'get_prefetch_queryset'):
prefetcher = rel_obj
is_fetched = attr in instance._prefetched_objects_cache
return prefetcher, rel_obj_descriptor, attr_found, is_fetched
@ -1597,6 +1598,7 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
else:
if as_attr:
setattr(obj, to_attr, vals)
obj._prefetched_objects_cache[cache_name] = vals
else:
# Cache in the QuerySet.all().
qs = getattr(obj, to_attr).all()

79
tests/prefetch_related/tests.py
View File

@ -1241,3 +1241,82 @@ class Ticket21760Tests(TestCase):
prefetcher = get_prefetcher(self.rooms[0], '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])
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])