def test_foreignkey_reverse(self):
books = list(Book.objects.all())
with self.assertNumQueries(1):
prefetch_related_objects(books, 'first_time_authors')
with self.assertNumQueries(0):
[list(book.first_time_authors.all()) for book in books]
def test_foreignkey_forward(self):
authors = list(Author.objects.all())
with self.assertNumQueries(1):
prefetch_related_objects(authors, 'first_book')
with self.assertNumQueries(0):
[author.first_book for author in authors]
def test_prefetch_object(self):
book1 = Book.objects.get(id=self.book1.id)
with self.assertNumQueries(1):
prefetch_related_objects([book1], Prefetch('authors'))
with self.assertNumQueries(0):
self.assertCountEqual(book1.authors.all(),
[self.author1, self.author2, self.author3])
def test_m2m_reverse(self):
author1 = Author.objects.get(id=self.author1.id)
with self.assertNumQueries(1):
prefetch_related_objects([author1], 'books')
with self.assertNumQueries(0):
self.assertCountEqual(author1.books.all(),
[self.book1, self.book2])
def test_prefetch_queryset(self):
book1 = Book.objects.get(id=self.book1.id)
with self.assertNumQueries(1):
prefetch_related_objects(
[book1],
Prefetch('authors',
queryset=Author.objects.filter(
id__in=[self.author1.id, self.author2.id])))
with self.assertNumQueries(0):
self.assertCountEqual(book1.authors.all(),
[self.author1, self.author2])
def test_m2m_then_m2m(self):
"""A m2m can be followed through another m2m."""
authors = list(Author.objects.all())
with self.assertNumQueries(2):
prefetch_related_objects(authors, 'books__read_by')
with self.assertNumQueries(0):
self.assertEqual(
[[[str(r) for r in b.read_by.all()] for b in a.books.all()]
for a in authors],
[
[['Amy'], ['Belinda']], # Charlotte - Poems, Jane Eyre
[['Amy']], # Anne - Poems
[['Amy'], []], # Emily - Poems, Wuthering Heights
[['Amy', 'Belinda']], # Jane - Sense and Sense
])
def test_unknown(self):
book1 = Book.objects.get(id=self.book1.id)
with self.assertRaises(AttributeError):
prefetch_related_objects([book1], 'unknown_attribute')