Fixed #25279 -- Made prefetch_related_objects() public.

tests/prefetch_related/test_prefetch_related_objects.py

@@ -0,0 +1,119 @@
+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):
+        """
+        We can follow a m2m and 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})