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from django.db.models import Prefetch, prefetch_related_objects
from django.test import TestCase
from .models import Author, Book, Reader
class PrefetchRelatedObjectsTests(TestCase):
"""
Since prefetch_related_objects() is just the inner part of
prefetch_related(), only do basic tests to ensure its API hasn't changed.
"""
@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_unknown(self):
book1 = Book.objects.get(id=self.book1.id)
with self.assertRaises(AttributeError):
prefetch_related_objects([book1], 'unknown_attribute')
def test_m2m_forward(self):
book1 = Book.objects.get(id=self.book1.id)
with self.assertNumQueries(1):
prefetch_related_objects([book1], 'authors')
with self.assertNumQueries(0):
self.assertEqual(set(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.assertEqual(set(author1.books.all()), {self.book1, self.book2})
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_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_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_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.assertEqual(set(book1.authors.all()), {self.author1, self.author2, self.author3})
def test_prefetch_object_to_attr(self):
book1 = Book.objects.get(id=self.book1.id)
with self.assertNumQueries(1):
prefetch_related_objects([book1], Prefetch('authors', to_attr='the_authors'))
with self.assertNumQueries(0):
self.assertEqual(set(book1.the_authors), {self.author1, self.author2, self.author3})
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.assertEqual(set(book1.authors.all()), {self.author1, self.author2})
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