tests.py

from __future__ import absolute_import, unicode_literals

from django.contrib.contenttypes.models import ContentType
from django.db import connection
from django.test import TestCase
from django.test.utils import override_settings
from django.utils import six

from .models import (Author, Book, Reader, Qualification, Teacher, Department,
    TaggedItem, Bookmark, AuthorAddress, FavoriteAuthors, AuthorWithAge,
    BookWithYear, BookReview, Person, House, Room, Employee, Comment,
    LessonEntry, WordEntry, Author2)


class PrefetchRelatedTests(TestCase):

    def setUp(self):

        self.book1 = Book.objects.create(title="Poems")
        self.book2 = Book.objects.create(title="Jane Eyre")
        self.book3 = Book.objects.create(title="Wuthering Heights")
        self.book4 = Book.objects.create(title="Sense and Sensibility")

        self.author1 = Author.objects.create(name="Charlotte",
                                             first_book=self.book1)
        self.author2 = Author.objects.create(name="Anne",
                                             first_book=self.book1)
        self.author3 = Author.objects.create(name="Emily",
                                             first_book=self.book1)
        self.author4 = Author.objects.create(name="Jane",
                                             first_book=self.book4)

        self.book1.authors.add(self.author1, self.author2, self.author3)
        self.book2.authors.add(self.author1)
        self.book3.authors.add(self.author3)
        self.book4.authors.add(self.author4)

        self.reader1 = Reader.objects.create(name="Amy")
        self.reader2 = Reader.objects.create(name="Belinda")

        self.reader1.books_read.add(self.book1, self.book4)
        self.reader2.books_read.add(self.book2, self.book4)

    def test_m2m_forward(self):
        with self.assertNumQueries(2):
            lists = [list(b.authors.all()) for b in Book.objects.prefetch_related('authors')]

        normal_lists = [list(b.authors.all()) for b in Book.objects.all()]
        self.assertEqual(lists, normal_lists)


    def test_m2m_reverse(self):
        with self.assertNumQueries(2):
            lists = [list(a.books.all()) for a in Author.objects.prefetch_related('books')]

        normal_lists = [list(a.books.all()) for a in Author.objects.all()]
        self.assertEqual(lists, normal_lists)

    def test_foreignkey_forward(self):
        with self.assertNumQueries(2):
            books = [a.first_book for a in Author.objects.prefetch_related('first_book')]

        normal_books = [a.first_book for a in Author.objects.all()]
        self.assertEqual(books, normal_books)

    def test_foreignkey_reverse(self):
        with self.assertNumQueries(2):
            lists = [list(b.first_time_authors.all())
                     for b in Book.objects.prefetch_related('first_time_authors')]

        self.assertQuerysetEqual(self.book2.authors.all(), ["<Author: Charlotte>"])

    def test_onetoone_reverse_no_match(self):
        # Regression for #17439
        with self.assertNumQueries(2):
            book = Book.objects.prefetch_related('bookwithyear').all()[0]
        with self.assertNumQueries(0):
            with self.assertRaises(BookWithYear.DoesNotExist):
                book.bookwithyear

    def test_survives_clone(self):
        with self.assertNumQueries(2):
            lists = [list(b.first_time_authors.all())
                     for b in Book.objects.prefetch_related('first_time_authors').exclude(id=1000)]

    def test_len(self):
        with self.assertNumQueries(2):
            qs = Book.objects.prefetch_related('first_time_authors')
            length = len(qs)
            lists = [list(b.first_time_authors.all())
                     for b in qs]

    def test_bool(self):
        with self.assertNumQueries(2):
            qs = Book.objects.prefetch_related('first_time_authors')
            x = bool(qs)
            lists = [list(b.first_time_authors.all())
                     for b in qs]

    def test_count(self):
        with self.assertNumQueries(2):
            qs = Book.objects.prefetch_related('first_time_authors')
            [b.first_time_authors.count() for b in qs]

    def test_exists(self):
        with self.assertNumQueries(2):
            qs = Book.objects.prefetch_related('first_time_authors')
            [b.first_time_authors.exists() for b in qs]

    def test_in_and_prefetch_related(self):
        """
        Regression test for #20242 - QuerySet "in" didn't work the first time
        when using prefetch_related. This was fixed by the removal of chunked
        reads from QuerySet iteration in
        70679243d1786e03557c28929f9762a119e3ac14.
        """
        qs = Book.objects.prefetch_related('first_time_authors')
        self.assertTrue(qs[0] in qs)

    def test_clear(self):
        """
        Test that we can clear the behavior by calling prefetch_related()
        """
        with self.assertNumQueries(5):
            with_prefetch = Author.objects.prefetch_related('books')
            without_prefetch = with_prefetch.prefetch_related(None)
            lists = [list(a.books.all()) for a in without_prefetch]

    def test_m2m_then_m2m(self):
        """
        Test we can follow a m2m and another m2m
        """
        with self.assertNumQueries(3):
            qs = Author.objects.prefetch_related('books__read_by')
            lists = [[[six.text_type(r) for r in b.read_by.all()]
                      for b in a.books.all()]
                     for a in qs]
            self.assertEqual(lists,
            [
                [["Amy"], ["Belinda"]],  # Charlotte - Poems, Jane Eyre
                [["Amy"]],                # Anne - Poems
                [["Amy"], []],            # Emily - Poems, Wuthering Heights
                [["Amy", "Belinda"]],    # Jane - Sense and Sense
            ])

    def test_overriding_prefetch(self):
        with self.assertNumQueries(3):
            qs = Author.objects.prefetch_related('books', 'books__read_by')
            lists = [[[six.text_type(r) for r in b.read_by.all()]
                      for b in a.books.all()]
                     for a in qs]
            self.assertEqual(lists,
            [
                [["Amy"], ["Belinda"]],  # Charlotte - Poems, Jane Eyre
                [["Amy"]],                # Anne - Poems
                [["Amy"], []],            # Emily - Poems, Wuthering Heights
                [["Amy", "Belinda"]],    # Jane - Sense and Sense
            ])
        with self.assertNumQueries(3):
            qs = Author.objects.prefetch_related('books__read_by', 'books')
            lists = [[[six.text_type(r) for r in b.read_by.all()]
                      for b in a.books.all()]
                     for a in qs]
            self.assertEqual(lists,
            [
                [["Amy"], ["Belinda"]],  # Charlotte - Poems, Jane Eyre
                [["Amy"]],                # Anne - Poems
                [["Amy"], []],            # Emily - Poems, Wuthering Heights
                [["Amy", "Belinda"]],    # Jane - Sense and Sense
            ])

    def test_get(self):
        """
        Test that objects retrieved with .get() get the prefetch behavior.
        """
        # Need a double
        with self.assertNumQueries(3):
            author = Author.objects.prefetch_related('books__read_by').get(name="Charlotte")
            lists = [[six.text_type(r) for r in b.read_by.all()]
                      for b in author.books.all()]
            self.assertEqual(lists, [["Amy"], ["Belinda"]])  # Poems, Jane Eyre

    def test_foreign_key_then_m2m(self):
        """
        Test we can follow an m2m relation after a relation like ForeignKey
        that doesn't have many objects
        """
        with self.assertNumQueries(2):
            qs = Author.objects.select_related('first_book').prefetch_related('first_book__read_by')
            lists = [[six.text_type(r) for r in a.first_book.read_by.all()]
                     for a in qs]
            self.assertEqual(lists, [["Amy"],
                                     ["Amy"],
                                     ["Amy"],
                                     ["Amy", "Belinda"]])

    def test_attribute_error(self):
        qs = Reader.objects.all().prefetch_related('books_read__xyz')
        with self.assertRaises(AttributeError) as cm:
            list(qs)

        self.assertTrue('prefetch_related' in str(cm.exception))

    def test_invalid_final_lookup(self):
        qs = Book.objects.prefetch_related('authors__name')
        with self.assertRaises(ValueError) as cm:
            list(qs)

        self.assertTrue('prefetch_related' in str(cm.exception))
        self.assertTrue("name" in str(cm.exception))


class DefaultManagerTests(TestCase):

    def setUp(self):
        self.qual1 = Qualification.objects.create(name="BA")
        self.qual2 = Qualification.objects.create(name="BSci")
        self.qual3 = Qualification.objects.create(name="MA")
        self.qual4 = Qualification.objects.create(name="PhD")

        self.teacher1 = Teacher.objects.create(name="Mr Cleese")
        self.teacher2 = Teacher.objects.create(name="Mr Idle")
        self.teacher3 = Teacher.objects.create(name="Mr Chapman")

        self.teacher1.qualifications.add(self.qual1, self.qual2, self.qual3, self.qual4)
        self.teacher2.qualifications.add(self.qual1)
        self.teacher3.qualifications.add(self.qual2)

        self.dept1 = Department.objects.create(name="English")
        self.dept2 = Department.objects.create(name="Physics")

        self.dept1.teachers.add(self.teacher1, self.teacher2)
        self.dept2.teachers.add(self.teacher1, self.teacher3)

    def test_m2m_then_m2m(self):
        with self.assertNumQueries(3):
            # When we prefetch the teachers, and force the query, we don't want
            # the default manager on teachers to immediately get all the related
            # qualifications, since this will do one query per teacher.
            qs = Department.objects.prefetch_related('teachers')
            depts = "".join(["%s department: %s\n" %
                             (dept.name, ", ".join(six.text_type(t) for t in dept.teachers.all()))
                             for dept in qs])

            self.assertEqual(depts,
                             "English department: Mr Cleese (BA, BSci, MA, PhD), Mr Idle (BA)\n"
                             "Physics department: Mr Cleese (BA, BSci, MA, PhD), Mr Chapman (BSci)\n")


class GenericRelationTests(TestCase):

    def setUp(self):
        book1 = Book.objects.create(title="Winnie the Pooh")
        book2 = Book.objects.create(title="Do you like green eggs and spam?")
        book3 = Book.objects.create(title="Three Men In A Boat")

        reader1 = Reader.objects.create(name="me")
        reader2 = Reader.objects.create(name="you")
        reader3 = Reader.objects.create(name="someone")

        book1.read_by.add(reader1, reader2)
        book2.read_by.add(reader2)
        book3.read_by.add(reader3)

        self.book1, self.book2, self.book3 = book1, book2, book3
        self.reader1, self.reader2, self.reader3 = reader1, reader2, reader3

    def test_prefetch_GFK(self):
        TaggedItem.objects.create(tag="awesome", content_object=self.book1)
        TaggedItem.objects.create(tag="great", content_object=self.reader1)
        TaggedItem.objects.create(tag="stupid", content_object=self.book2)
        TaggedItem.objects.create(tag="amazing", content_object=self.reader3)

        # 1 for TaggedItem table, 1 for Book table, 1 for Reader table
        with self.assertNumQueries(3):
            qs = TaggedItem.objects.prefetch_related('content_object')
            list(qs)

    def test_prefetch_GFK_nonint_pk(self):
        Comment.objects.create(comment="awesome", content_object=self.book1)

        # 1 for Comment table, 1 for Book table
        with self.assertNumQueries(2):
            qs = Comment.objects.prefetch_related('content_object')
            [c.content_object for c in qs]

    def test_traverse_GFK(self):
        """
        Test that we can traverse a 'content_object' with prefetch_related() and
        get to related objects on the other side (assuming it is suitably
        filtered)
        """
        TaggedItem.objects.create(tag="awesome", content_object=self.book1)
        TaggedItem.objects.create(tag="awesome", content_object=self.book2)
        TaggedItem.objects.create(tag="awesome", content_object=self.book3)
        TaggedItem.objects.create(tag="awesome", content_object=self.reader1)
        TaggedItem.objects.create(tag="awesome", content_object=self.reader2)

        ct = ContentType.objects.get_for_model(Book)

        # We get 3 queries - 1 for main query, 1 for content_objects since they
        # all use the same table, and 1 for the 'read_by' relation.
        with self.assertNumQueries(3):
            # If we limit to books, we know that they will have 'read_by'
            # attributes, so the following makes sense:
            qs = TaggedItem.objects.filter(content_type=ct, tag='awesome').prefetch_related('content_object__read_by')
            readers_of_awesome_books = set([r.name for tag in qs
                                            for r in tag.content_object.read_by.all()])
            self.assertEqual(readers_of_awesome_books, set(["me", "you", "someone"]))

    def test_nullable_GFK(self):
        TaggedItem.objects.create(tag="awesome", content_object=self.book1,
                                  created_by=self.reader1)
        TaggedItem.objects.create(tag="great", content_object=self.book2)
        TaggedItem.objects.create(tag="rubbish", content_object=self.book3)

        with self.assertNumQueries(2):
            result = [t.created_by for t in TaggedItem.objects.prefetch_related('created_by')]

        self.assertEqual(result,
                         [t.created_by for t in TaggedItem.objects.all()])

    def test_generic_relation(self):
        b = Bookmark.objects.create(url='http://www.djangoproject.com/')
        t1 = TaggedItem.objects.create(content_object=b, tag='django')
        t2 = TaggedItem.objects.create(content_object=b, tag='python')

        with self.assertNumQueries(2):
            tags = [t.tag for b in Bookmark.objects.prefetch_related('tags')
                    for t in b.tags.all()]
            self.assertEqual(sorted(tags), ["django", "python"])

    def test_charfield_GFK(self):
        b = Bookmark.objects.create(url='http://www.djangoproject.com/')
        t1 = TaggedItem.objects.create(content_object=b, tag='django')
        t2 = TaggedItem.objects.create(content_object=b, favorite=b, tag='python')

        with self.assertNumQueries(3):
            bookmark = Bookmark.objects.filter(pk=b.pk).prefetch_related('tags', 'favorite_tags')[0]
            self.assertEqual(sorted([i.tag for i in bookmark.tags.all()]), ["django", "python"])
            self.assertEqual([i.tag for i in bookmark.favorite_tags.all()], ["python"])


class MultiTableInheritanceTest(TestCase):

    def setUp(self):
        self.book1 = BookWithYear.objects.create(
            title="Poems", published_year=2010)
        self.book2 = BookWithYear.objects.create(
            title="More poems", published_year=2011)
        self.author1 = AuthorWithAge.objects.create(
            name='Jane', first_book=self.book1, age=50)
        self.author2 = AuthorWithAge.objects.create(
            name='Tom', first_book=self.book1, age=49)
        self.author3 = AuthorWithAge.objects.create(
            name='Robert', first_book=self.book2, age=48)
        self.authorAddress = AuthorAddress.objects.create(
            author=self.author1, address='SomeStreet 1')
        self.book2.aged_authors.add(self.author2, self.author3)
        self.br1 = BookReview.objects.create(
            book=self.book1, notes="review book1")
        self.br2 = BookReview.objects.create(
            book=self.book2, notes="review book2")

    def test_foreignkey(self):
        with self.assertNumQueries(2):
            qs = AuthorWithAge.objects.prefetch_related('addresses')
            addresses = [[six.text_type(address) for address in obj.addresses.all()]
                         for obj in qs]
        self.assertEqual(addresses, [[six.text_type(self.authorAddress)], [], []])

    def test_foreignkey_to_inherited(self):
        with self.assertNumQueries(2):
            qs = BookReview.objects.prefetch_related('book')
            titles = [obj.book.title for obj in qs]
        self.assertEqual(titles, ["Poems", "More poems"])

    def test_m2m_to_inheriting_model(self):
        qs = AuthorWithAge.objects.prefetch_related('books_with_year')
        with self.assertNumQueries(2):
            lst = [[six.text_type(book) for book in author.books_with_year.all()]
                   for author in qs]
        qs = AuthorWithAge.objects.all()
        lst2 = [[six.text_type(book) for book in author.books_with_year.all()]
                for author in qs]
        self.assertEqual(lst, lst2)

        qs = BookWithYear.objects.prefetch_related('aged_authors')
        with self.assertNumQueries(2):
            lst = [[six.text_type(author) for author in book.aged_authors.all()]
                   for book in qs]
        qs = BookWithYear.objects.all()
        lst2 = [[six.text_type(author) for author in book.aged_authors.all()]
               for book in qs]
        self.assertEqual(lst, lst2)

    def test_parent_link_prefetch(self):
        with self.assertNumQueries(2):
            [a.author for a in AuthorWithAge.objects.prefetch_related('author')]

    @override_settings(DEBUG=True)
    def test_child_link_prefetch(self):
        with self.assertNumQueries(2):
            l = [a.authorwithage for a in Author.objects.prefetch_related('authorwithage')]

        # Regression for #18090: the prefetching query must include an IN clause.
        # Note that on Oracle the table name is upper case in the generated SQL,
        # thus the .lower() call.
        self.assertIn('authorwithage', connection.queries[-1]['sql'].lower())
        self.assertIn(' IN ', connection.queries[-1]['sql'])

        self.assertEqual(l, [a.authorwithage for a in Author.objects.all()])


class ForeignKeyToFieldTest(TestCase):

    def setUp(self):
        self.book = Book.objects.create(title="Poems")
        self.author1 = Author.objects.create(name='Jane', first_book=self.book)
        self.author2 = Author.objects.create(name='Tom', first_book=self.book)
        self.author3 = Author.objects.create(name='Robert', first_book=self.book)
        self.authorAddress = AuthorAddress.objects.create(
            author=self.author1, address='SomeStreet 1'
        )
        FavoriteAuthors.objects.create(author=self.author1,
                                       likes_author=self.author2)
        FavoriteAuthors.objects.create(author=self.author2,
                                       likes_author=self.author3)
        FavoriteAuthors.objects.create(author=self.author3,
                                       likes_author=self.author1)

    def test_foreignkey(self):
        with self.assertNumQueries(2):
            qs = Author.objects.prefetch_related('addresses')
            addresses = [[six.text_type(address) for address in obj.addresses.all()]
                         for obj in qs]
        self.assertEqual(addresses, [[six.text_type(self.authorAddress)], [], []])

    def test_m2m(self):
        with self.assertNumQueries(3):
            qs = Author.objects.all().prefetch_related('favorite_authors', 'favors_me')
            favorites = [(
                 [six.text_type(i_like) for i_like in author.favorite_authors.all()],
                 [six.text_type(likes_me) for likes_me in author.favors_me.all()]
                ) for author in qs]
            self.assertEqual(
                favorites,
                [
                    ([six.text_type(self.author2)],[six.text_type(self.author3)]),
                    ([six.text_type(self.author3)],[six.text_type(self.author1)]),
                    ([six.text_type(self.author1)],[six.text_type(self.author2)])
                ]
            )


class LookupOrderingTest(TestCase):
    """
    Test cases that demonstrate that ordering of lookups is important, and
    ensure it is preserved.
    """

    def setUp(self):
        self.person1 = Person.objects.create(name="Joe")
        self.person2 = Person.objects.create(name="Mary")

        self.house1 = House.objects.create(address="123 Main St")
        self.house2 = House.objects.create(address="45 Side St")
        self.house3 = House.objects.create(address="6 Downing St")
        self.house4 = House.objects.create(address="7 Regents St")

        self.room1_1 = Room.objects.create(name="Dining room", house=self.house1)
        self.room1_2 = Room.objects.create(name="Lounge", house=self.house1)
        self.room1_3 = Room.objects.create(name="Kitchen", house=self.house1)

        self.room2_1 = Room.objects.create(name="Dining room", house=self.house2)
        self.room2_2 = Room.objects.create(name="Lounge", house=self.house2)

        self.room3_1 = Room.objects.create(name="Dining room", house=self.house3)
        self.room3_2 = Room.objects.create(name="Lounge", house=self.house3)
        self.room3_3 = Room.objects.create(name="Kitchen", house=self.house3)

        self.room4_1 = Room.objects.create(name="Dining room", house=self.house4)
        self.room4_2 = Room.objects.create(name="Lounge", house=self.house4)

        self.person1.houses.add(self.house1, self.house2)
        self.person2.houses.add(self.house3, self.house4)

    def test_order(self):
        with self.assertNumQueries(4):
            # The following two queries must be done in the same order as written,
            # otherwise 'primary_house' will cause non-prefetched lookups
            qs = Person.objects.prefetch_related('houses__rooms',
                                                 'primary_house__occupants')
            [list(p.primary_house.occupants.all()) for p in qs]


class NullableTest(TestCase):

    def setUp(self):
        boss = Employee.objects.create(name="Peter")
        worker1 = Employee.objects.create(name="Joe", boss=boss)
        worker2 = Employee.objects.create(name="Angela", boss=boss)

    def test_traverse_nullable(self):
        # Because we use select_related() for 'boss', it doesn't need to be
        # prefetched, but we can still traverse it although it contains some nulls
        with self.assertNumQueries(2):
            qs = Employee.objects.select_related('boss').prefetch_related('boss__serfs')
            co_serfs = [list(e.boss.serfs.all()) if e.boss is not None else []
                        for e in qs]

        qs2 =  Employee.objects.select_related('boss')
        co_serfs2 =  [list(e.boss.serfs.all()) if e.boss is not None else []
                        for e in qs2]

        self.assertEqual(co_serfs, co_serfs2)

    def test_prefetch_nullable(self):
        # One for main employee, one for boss, one for serfs
        with self.assertNumQueries(3):
            qs = Employee.objects.prefetch_related('boss__serfs')
            co_serfs = [list(e.boss.serfs.all()) if e.boss is not None else []
                        for e in qs]

        qs2 =  Employee.objects.all()
        co_serfs2 =  [list(e.boss.serfs.all()) if e.boss is not None else []
                        for e in qs2]

        self.assertEqual(co_serfs, co_serfs2)

    def test_in_bulk(self):
        """
        In-bulk does correctly prefetch objects by not using .iterator()
        directly.
        """
        boss1 = Employee.objects.create(name="Peter")
        boss2 = Employee.objects.create(name="Jack")
        with self.assertNumQueries(2):
            # Check that prefetch is done and it does not cause any errors.
            bulk = Employee.objects.prefetch_related('serfs').in_bulk([boss1.pk, boss2.pk])
            for b in bulk.values():
                list(b.serfs.all())


class MultiDbTests(TestCase):
    multi_db = True

    def test_using_is_honored_m2m(self):
        B = Book.objects.using('other')
        A = Author.objects.using('other')
        book1 = B.create(title="Poems")
        book2 = B.create(title="Jane Eyre")
        book3 = B.create(title="Wuthering Heights")
        book4 = B.create(title="Sense and Sensibility")

        author1 = A.create(name="Charlotte", first_book=book1)
        author2 = A.create(name="Anne", first_book=book1)
        author3 = A.create(name="Emily", first_book=book1)
        author4 = A.create(name="Jane", first_book=book4)

        book1.authors.add(author1, author2, author3)
        book2.authors.add(author1)
        book3.authors.add(author3)
        book4.authors.add(author4)

        # Forward
        qs1 = B.prefetch_related('authors')
        with self.assertNumQueries(2, using='other'):
            books = "".join(["%s (%s)\n" %
                             (book.title, ", ".join(a.name for a in book.authors.all()))
                             for book in qs1])
        self.assertEqual(books,
                         "Poems (Charlotte, Anne, Emily)\n"
                         "Jane Eyre (Charlotte)\n"
                         "Wuthering Heights (Emily)\n"
                         "Sense and Sensibility (Jane)\n")

        # Reverse
        qs2 = A.prefetch_related('books')
        with self.assertNumQueries(2, using='other'):
            authors = "".join(["%s: %s\n" %
                               (author.name, ", ".join(b.title for b in author.books.all()))
                               for author in qs2])
        self.assertEqual(authors,
                          "Charlotte: Poems, Jane Eyre\n"
                          "Anne: Poems\n"
                          "Emily: Poems, Wuthering Heights\n"
                          "Jane: Sense and Sensibility\n")

    def test_using_is_honored_fkey(self):
        B = Book.objects.using('other')
        A = Author.objects.using('other')
        book1 = B.create(title="Poems")
        book2 = B.create(title="Sense and Sensibility")

        author1 = A.create(name="Charlotte Bronte", first_book=book1)
        author2 = A.create(name="Jane Austen", first_book=book2)

        # Forward
        with self.assertNumQueries(2, using='other'):
            books = ", ".join(a.first_book.title for a in A.prefetch_related('first_book'))
        self.assertEqual("Poems, Sense and Sensibility", books)

        # Reverse
        with self.assertNumQueries(2, using='other'):
            books = "".join("%s (%s)\n" %
                            (b.title, ", ".join(a.name for a in b.first_time_authors.all()))
                            for b in B.prefetch_related('first_time_authors'))
        self.assertEqual(books,
                         "Poems (Charlotte Bronte)\n"
                         "Sense and Sensibility (Jane Austen)\n")

    def test_using_is_honored_inheritance(self):
        B = BookWithYear.objects.using('other')
        A = AuthorWithAge.objects.using('other')
        book1 = B.create(title="Poems", published_year=2010)
        book2 = B.create(title="More poems", published_year=2011)
        author1 = A.create(name='Jane', first_book=book1, age=50)
        author2 = A.create(name='Tom', first_book=book1, age=49)

        # parent link
        with self.assertNumQueries(2, using='other'):
            authors = ", ".join(a.author.name for a in A.prefetch_related('author'))

        self.assertEqual(authors, "Jane, Tom")

        # child link
        with self.assertNumQueries(2, using='other'):
            ages = ", ".join(str(a.authorwithage.age) for a in A.prefetch_related('authorwithage'))

        self.assertEqual(ages, "50, 49")


class Ticket19607Tests(TestCase):

    def setUp(self):

        for id, name1, name2 in [
            (1, 'einfach', 'simple'),
            (2, 'schwierig', 'difficult'),
            ]:
            LessonEntry.objects.create(id=id, name1=name1, name2=name2)

        for id, lesson_entry_id, name in [
            (1, 1, 'einfach'),
            (2, 1, 'simple'),
            (3, 2, 'schwierig'),
            (4, 2, 'difficult'),
            ]:
            WordEntry.objects.create(id=id, lesson_entry_id=lesson_entry_id, name=name)

    def test_bug(self):
        list(WordEntry.objects.prefetch_related('lesson_entry', 'lesson_entry__wordentry_set'))


class Ticket21410Tests(TestCase):

    def setUp(self):
        self.book1 = Book.objects.create(title="Poems")
        self.book2 = Book.objects.create(title="Jane Eyre")
        self.book3 = Book.objects.create(title="Wuthering Heights")
        self.book4 = Book.objects.create(title="Sense and Sensibility")

        self.author1 = Author2.objects.create(name="Charlotte",
                                             first_book=self.book1)
        self.author2 = Author2.objects.create(name="Anne",
                                             first_book=self.book1)
        self.author3 = Author2.objects.create(name="Emily",
                                             first_book=self.book1)
        self.author4 = Author2.objects.create(name="Jane",
                                             first_book=self.book4)

        self.author1.favorite_books.add(self.book1, self.book2, self.book3)
        self.author2.favorite_books.add(self.book1)
        self.author3.favorite_books.add(self.book2)
        self.author4.favorite_books.add(self.book3)

    def test_bug(self):
        list(Author2.objects.prefetch_related('first_book', 'favorite_books'))