Repository: django/django
File: tests/prefetch_related/test_prefetch_related_objects.py (Python)

Code before:
        prefetch_related_objects(deque([book]), "authors")
        self.assertCountEqual(
            book.authors.all(), [self.author1, self.author2, self.author3]
        )

        # custom iterable
        class MyIterable:
            def __iter__(self_inner):
                yield book

        prefetch_related_objects(MyIterable(), "authors")
        self.assertCountEqual(
            book.authors.all(), [self.author1, self.author2, self.author3]
        )

        # empty iterable
        prefetch_related_objects([], "authors")
        prefetch_related_objects(set(), "authors")
        prefetch_related_objects((), "authors")
        prefetch_related_objects(frozenset(), "authors")
        prefetch_related_objects({}.values(), "authors")
        prefetch_related_objects((x for x in []), "authors")
        prefetch_related_objects(map(lambda x: x, []), "authors")
        prefetch_related_objects(filter(lambda x: True, []), "authors")
        prefetch_related_objects(deque([]), "authors")
        prefetch_related_objects([book, book, book], "authors")


Review comment (suggestion):
Note that this is under the " # empty iterable" comment but is not an empty iterable. There's no asserts, other than you showing that this doesn't error, not sure what is being tested here

Code after:
from collections import deque

from django.db.models import Prefetch, prefetch_related_objects
from django.test import TestCase

from .models import Author, Book, House, Reader, Room


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)

        cls.house1 = House.objects.create(name="b1", address="1")
        cls.house2 = House.objects.create(name="b2", address="2")

        cls.room1 = Room.objects.create(name="a1", house=cls.house1)
        cls.room2 = Room.objects.create(name="a2", house=cls.house2)

        cls.house1.main_room = cls.room1
        cls.house1.save()
        cls.house2.main_room = cls.room2
        cls.house2.save()

    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) as ctx:
            prefetch_related_objects(authors, "first_book")
        self.assertNotIn("ORDER BY", ctx.captured_queries[0]["sql"])

        with self.assertNumQueries(0):
            [author.first_book for author in authors]

        authors = list(Author.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(
                authors,
                Prefetch("first_book", queryset=Book.objects.order_by("-title")),
            )
        self.assertNotIn("ORDER BY", ctx.captured_queries[0]["sql"])

    def test_foreignkey_reverse(self):
        books = list(Book.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(books, "first_time_authors")
        self.assertIn("ORDER BY", ctx.captured_queries[0]["sql"])

        with self.assertNumQueries(0):
            [list(book.first_time_authors.all()) for book in books]

        books = list(Book.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(
                books,
                Prefetch(
                    "first_time_authors",
                    queryset=Author.objects.order_by("-name"),
                ),
            )
        self.assertIn("ORDER BY", ctx.captured_queries[0]["sql"])

    def test_one_to_one_forward(self):
        houses = list(House.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(houses, "main_room")
        self.assertNotIn("ORDER BY", ctx.captured_queries[0]["sql"])

        with self.assertNumQueries(0):
            [house.main_room for house in houses]

        houses = list(House.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(
                houses,
                Prefetch("main_room", queryset=Room.objects.order_by("-name")),
            )
        self.assertNotIn("ORDER BY", ctx.captured_queries[0]["sql"])

    def test_one_to_one_reverse(self):
        rooms = list(Room.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(rooms, "main_room_of")
        self.assertNotIn("ORDER BY", ctx.captured_queries[0]["sql"])

        with self.assertNumQueries(0):
            [room.main_room_of for room in rooms]

        rooms = list(Room.objects.all())
        with self.assertNumQueries(1) as ctx:
            prefetch_related_objects(
                rooms,
                Prefetch("main_room_of", queryset=House.objects.order_by("-name")),
            )
        self.assertNotIn("ORDER BY", ctx.captured_queries[0]["sql"])

    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])

    def test_prefetch_related_objects_with_various_iterables(self):
        book = self.book1

        class MyIterable:
            def __iter__(self):
                yield book

        cases = {
            "set": {book},
            "tuple": (book,),
            "dict_values": {"a": book}.values(),
            "frozenset": frozenset([book]),
            "deque": deque([book]),
            "custom iterator": MyIterable(),
        }
        for case_type, case in cases.items():
            with self.subTest(case=case_type):
                # Clear the prefetch cache.
                book._prefetched_objects_cache = {}
                with self.assertNumQueries(1):
                    prefetch_related_objects(case, "authors")
                with self.assertNumQueries(0):
                    self.assertCountEqual(
                        book.authors.all(), [self.author1, self.author2, self.author3]
                    )

    def test_prefetch_related_objects_empty(self):
        prefetch_related_objects([], "authors")