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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.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_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.assertCountEqual(
book1.authors.all(), [self.author1, self.author2, self.author3]
)
def test_prefetch_object_twice(self):
book1 = Book.objects.get(id=self.book1.id)
book2 = Book.objects.get(id=self.book2.id)
with self.assertNumQueries(1):
prefetch_related_objects([book1], Prefetch("authors"))
with self.assertNumQueries(1):
prefetch_related_objects([book1, book2], Prefetch("authors"))
with self.assertNumQueries(0):
self.assertCountEqual(book2.authors.all(), [self.author1])
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.assertCountEqual(
book1.the_authors, [self.author1, self.author2, self.author3]
)
def test_prefetch_object_to_attr_twice(self):
book1 = Book.objects.get(id=self.book1.id)
book2 = Book.objects.get(id=self.book2.id)
with self.assertNumQueries(1):
prefetch_related_objects(
[book1],
Prefetch("authors", to_attr="the_authors"),
)
with self.assertNumQueries(1):
prefetch_related_objects(
[book1, book2],
Prefetch("authors", to_attr="the_authors"),
)
with self.assertNumQueries(0):
self.assertCountEqual(book2.the_authors, [self.author1])
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])
|
