django/tests/many_to_one/tests.py

import datetime
from copy import deepcopy

from django.core.exceptions import (
    FieldError,
    FieldFetchBlocked,
    MultipleObjectsReturned,
)
from django.db import IntegrityError, models, transaction
from django.db.models import FETCH_PEERS, RAISE
from django.test import TestCase
from django.utils.translation import gettext_lazy

from .models import (
    Article,
    Category,
    Child,
    ChildNullableParent,
    ChildStringPrimaryKeyParent,
    City,
    Country,
    District,
    First,
    Parent,
    ParentStringPrimaryKey,
    Record,
    Relation,
    Reporter,
    School,
    Student,
    Third,
    ToFieldChild,
)


class ManyToOneTests(TestCase):
    @classmethod
    def setUpTestData(cls):
        # Create a few Reporters.
        cls.r = Reporter(first_name="John", last_name="Smith", email="john@example.com")
        cls.r.save()
        cls.r2 = Reporter(
            first_name="Paul", last_name="Jones", email="paul@example.com"
        )
        cls.r2.save()
        # Create an Article.
        cls.a = Article(
            headline="This is a test",
            pub_date=datetime.date(2005, 7, 27),
            reporter=cls.r,
        )
        cls.a.save()

    def test_get(self):
        # Article objects have access to their related Reporter objects.
        r = self.a.reporter
        self.assertEqual(r.id, self.r.id)
        self.assertEqual((r.first_name, self.r.last_name), ("John", "Smith"))

    def test_create(self):
        # You can also instantiate an Article by passing the Reporter's ID
        # instead of a Reporter object.
        a3 = Article(
            headline="Third article",
            pub_date=datetime.date(2005, 7, 27),
            reporter_id=self.r.id,
        )
        a3.save()
        self.assertEqual(a3.reporter.id, self.r.id)

        # Similarly, the reporter ID can be a string.
        a4 = Article(
            headline="Fourth article",
            pub_date=datetime.date(2005, 7, 27),
            reporter_id=str(self.r.id),
        )
        a4.save()
        self.assertEqual(repr(a4.reporter), "<Reporter: John Smith>")

    def test_add(self):
        # Create an Article via the Reporter object.
        new_article = self.r.article_set.create(
            headline="John's second story", pub_date=datetime.date(2005, 7, 29)
        )
        self.assertEqual(repr(new_article), "<Article: John's second story>")
        self.assertEqual(new_article.reporter.id, self.r.id)

        # Create a new article, and add it to the article set.
        new_article2 = Article(
            headline="Paul's story", pub_date=datetime.date(2006, 1, 17)
        )
        msg = (
            "<Article: Paul's story> instance isn't saved. Use bulk=False or save the "
            "object first."
        )
        with self.assertRaisesMessage(ValueError, msg):
            self.r.article_set.add(new_article2)

        self.r.article_set.add(new_article2, bulk=False)
        self.assertEqual(new_article2.reporter.id, self.r.id)
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article, new_article2, self.a],
        )

        # Add the same article to a different article set - check that it
        # moves.
        self.r2.article_set.add(new_article2)
        self.assertEqual(new_article2.reporter.id, self.r2.id)
        self.assertSequenceEqual(self.r2.article_set.all(), [new_article2])

        # Adding an object of the wrong type raises TypeError.
        with transaction.atomic():
            with self.assertRaisesMessage(
                TypeError, "'Article' instance expected, got <Reporter:"
            ):
                self.r.article_set.add(self.r2)
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article, self.a],
        )

    def test_set(self):
        new_article = self.r.article_set.create(
            headline="John's second story", pub_date=datetime.date(2005, 7, 29)
        )
        new_article2 = self.r2.article_set.create(
            headline="Paul's story", pub_date=datetime.date(2006, 1, 17)
        )

        # Assign the article to the reporter.
        new_article2.reporter = self.r
        new_article2.save()
        self.assertEqual(repr(new_article2.reporter), "<Reporter: John Smith>")
        self.assertEqual(new_article2.reporter.id, self.r.id)
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article, new_article2, self.a],
        )
        self.assertSequenceEqual(self.r2.article_set.all(), [])

        # Set the article back again.
        self.r2.article_set.set([new_article, new_article2])
        self.assertSequenceEqual(self.r.article_set.all(), [self.a])
        self.assertSequenceEqual(
            self.r2.article_set.all(),
            [new_article, new_article2],
        )

        # Funny case - because the ForeignKey cannot be null,
        # existing members of the set must remain.
        self.r.article_set.set([new_article])
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article, self.a],
        )
        self.assertSequenceEqual(self.r2.article_set.all(), [new_article2])

    def test_reverse_assignment_deprecation(self):
        msg = (
            "Direct assignment to the reverse side of a related set is "
            "prohibited. Use article_set.set() instead."
        )
        with self.assertRaisesMessage(TypeError, msg):
            self.r2.article_set = []

    def test_assign(self):
        new_article = self.r.article_set.create(
            headline="John's second story", pub_date=datetime.date(2005, 7, 29)
        )
        new_article2 = self.r2.article_set.create(
            headline="Paul's story", pub_date=datetime.date(2006, 1, 17)
        )

        # Assign the article to the reporter directly using the descriptor.
        new_article2.reporter = self.r
        new_article2.save()
        self.assertEqual(repr(new_article2.reporter), "<Reporter: John Smith>")
        self.assertEqual(new_article2.reporter.id, self.r.id)
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article, new_article2, self.a],
        )
        self.assertSequenceEqual(self.r2.article_set.all(), [])

        # Set the article back again using set() method.
        self.r2.article_set.set([new_article, new_article2])
        self.assertSequenceEqual(self.r.article_set.all(), [self.a])
        self.assertSequenceEqual(
            self.r2.article_set.all(),
            [new_article, new_article2],
        )

        # Because the ForeignKey cannot be null, existing members of the set
        # must remain.
        self.r.article_set.set([new_article])
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article, self.a],
        )
        self.assertSequenceEqual(self.r2.article_set.all(), [new_article2])
        # Reporter cannot be null - there should not be a clear or remove
        # method
        self.assertFalse(hasattr(self.r2.article_set, "remove"))
        self.assertFalse(hasattr(self.r2.article_set, "clear"))

    def test_assign_fk_id_value(self):
        parent = Parent.objects.create(name="jeff")
        child1 = Child.objects.create(name="frank", parent=parent)
        child2 = Child.objects.create(name="randy", parent=parent)
        parent.bestchild = child1
        parent.save()
        parent.bestchild_id = child2.pk
        parent.save()
        self.assertEqual(parent.bestchild_id, child2.pk)
        self.assertFalse(Parent.bestchild.is_cached(parent))
        self.assertEqual(parent.bestchild, child2)
        self.assertTrue(Parent.bestchild.is_cached(parent))
        # Reassigning the same value doesn't clear cached instance.
        parent.bestchild_id = child2.pk
        self.assertTrue(Parent.bestchild.is_cached(parent))

    def test_assign_fk_id_none(self):
        parent = Parent.objects.create(name="jeff")
        child = Child.objects.create(name="frank", parent=parent)
        parent.bestchild = child
        parent.save()
        parent.bestchild_id = None
        parent.save()
        self.assertIsNone(parent.bestchild_id)
        self.assertFalse(Parent.bestchild.is_cached(parent))
        self.assertIsNone(parent.bestchild)
        self.assertTrue(Parent.bestchild.is_cached(parent))

    def test_selects(self):
        new_article1 = self.r.article_set.create(
            headline="John's second story",
            pub_date=datetime.date(2005, 7, 29),
        )
        new_article2 = self.r2.article_set.create(
            headline="Paul's story",
            pub_date=datetime.date(2006, 1, 17),
        )
        # Reporter objects have access to their related Article objects.
        self.assertSequenceEqual(
            self.r.article_set.all(),
            [new_article1, self.a],
        )
        self.assertSequenceEqual(
            self.r.article_set.filter(headline__startswith="This"), [self.a]
        )
        self.assertEqual(self.r.article_set.count(), 2)
        self.assertEqual(self.r2.article_set.count(), 1)
        # Get articles by id
        self.assertSequenceEqual(Article.objects.filter(id__exact=self.a.id), [self.a])
        self.assertSequenceEqual(Article.objects.filter(pk=self.a.id), [self.a])
        # Query on an article property
        self.assertSequenceEqual(
            Article.objects.filter(headline__startswith="This"), [self.a]
        )
        # The API automatically follows relationships as far as you need.
        # Use double underscores to separate relationships.
        # This works as many levels deep as you want. There's no limit.
        # Find all Articles for any Reporter whose first name is "John".
        self.assertSequenceEqual(
            Article.objects.filter(reporter__first_name__exact="John"),
            [new_article1, self.a],
        )
        # Implied __exact also works
        self.assertSequenceEqual(
            Article.objects.filter(reporter__first_name="John"),
            [new_article1, self.a],
        )
        # Query twice over the related field.
        self.assertSequenceEqual(
            Article.objects.filter(
                reporter__first_name__exact="John", reporter__last_name__exact="Smith"
            ),
            [new_article1, self.a],
        )
        # The underlying query only makes one join when a related table is
        # referenced twice.
        queryset = Article.objects.filter(
            reporter__first_name__exact="John", reporter__last_name__exact="Smith"
        )
        self.assertNumQueries(1, list, queryset)
        self.assertEqual(
            queryset.query.get_compiler(queryset.db).as_sql()[0].count("INNER JOIN"), 1
        )

        # The automatically joined table has a predictable name.
        self.assertSequenceEqual(
            Article.objects.filter(reporter__first_name__exact="John").extra(
                where=["many_to_one_reporter.last_name='Smith'"]
            ),
            [new_article1, self.a],
        )
        # ... and should work fine with the string that comes out of
        # forms.Form.cleaned_data.
        self.assertQuerySetEqual(
            (
                Article.objects.filter(reporter__first_name__exact="John").extra(
                    where=["many_to_one_reporter.last_name='%s'" % "Smith"]
                )
            ),
            [new_article1, self.a],
        )
        # Find all Articles for a Reporter.
        # Use direct ID check, pk check, and object comparison
        self.assertSequenceEqual(
            Article.objects.filter(reporter__id__exact=self.r.id),
            [new_article1, self.a],
        )
        self.assertSequenceEqual(
            Article.objects.filter(reporter__pk=self.r.id),
            [new_article1, self.a],
        )
        self.assertSequenceEqual(
            Article.objects.filter(reporter=self.r.id),
            [new_article1, self.a],
        )
        self.assertSequenceEqual(
            Article.objects.filter(reporter=self.r),
            [new_article1, self.a],
        )
        self.assertSequenceEqual(
            Article.objects.filter(reporter__in=[self.r.id, self.r2.id]).distinct(),
            [new_article1, new_article2, self.a],
        )
        self.assertSequenceEqual(
            Article.objects.filter(reporter__in=[self.r, self.r2]).distinct(),
            [new_article1, new_article2, self.a],
        )
        # You can also use a queryset instead of a literal list of instances.
        # The queryset must be reduced to a list of values using values(),
        # then converted into a query
        self.assertSequenceEqual(
            Article.objects.filter(
                reporter__in=Reporter.objects.filter(first_name="John")
                .values("pk")
                .query
            ).distinct(),
            [new_article1, self.a],
        )

    def test_reverse_selects(self):
        a3 = Article.objects.create(
            headline="Third article",
            pub_date=datetime.date(2005, 7, 27),
            reporter_id=self.r.id,
        )
        Article.objects.create(
            headline="Fourth article",
            pub_date=datetime.date(2005, 7, 27),
            reporter_id=self.r.id,
        )
        john_smith = [self.r]
        # Reporters can be queried
        self.assertSequenceEqual(
            Reporter.objects.filter(id__exact=self.r.id), john_smith
        )
        self.assertSequenceEqual(Reporter.objects.filter(pk=self.r.id), john_smith)
        self.assertSequenceEqual(
            Reporter.objects.filter(first_name__startswith="John"), john_smith
        )
        # Reporters can query in opposite direction of ForeignKey definition
        self.assertSequenceEqual(
            Reporter.objects.filter(article__id__exact=self.a.id), john_smith
        )
        self.assertSequenceEqual(
            Reporter.objects.filter(article__pk=self.a.id), john_smith
        )
        self.assertSequenceEqual(Reporter.objects.filter(article=self.a.id), john_smith)
        self.assertSequenceEqual(Reporter.objects.filter(article=self.a), john_smith)
        self.assertSequenceEqual(
            Reporter.objects.filter(article__in=[self.a.id, a3.id]).distinct(),
            john_smith,
        )
        self.assertSequenceEqual(
            Reporter.objects.filter(article__in=[self.a.id, a3]).distinct(), john_smith
        )
        self.assertSequenceEqual(
            Reporter.objects.filter(article__in=[self.a, a3]).distinct(), john_smith
        )
        self.assertCountEqual(
            Reporter.objects.filter(article__headline__startswith="T"),
            [self.r, self.r],
        )
        self.assertSequenceEqual(
            Reporter.objects.filter(article__headline__startswith="T").distinct(),
            john_smith,
        )

        # Counting in the opposite direction works in conjunction with
        # distinct()
        self.assertEqual(
            Reporter.objects.filter(article__headline__startswith="T").count(), 2
        )
        self.assertEqual(
            Reporter.objects.filter(article__headline__startswith="T")
            .distinct()
            .count(),
            1,
        )

        # Queries can go round in circles.
        self.assertCountEqual(
            Reporter.objects.filter(article__reporter__first_name__startswith="John"),
            [self.r, self.r, self.r],
        )
        self.assertSequenceEqual(
            Reporter.objects.filter(
                article__reporter__first_name__startswith="John"
            ).distinct(),
            john_smith,
        )
        self.assertSequenceEqual(
            Reporter.objects.filter(article__reporter__exact=self.r).distinct(),
            john_smith,
        )

        # Implied __exact also works.
        self.assertSequenceEqual(
            Reporter.objects.filter(article__reporter=self.r).distinct(), john_smith
        )

        # It's possible to use values() calls across many-to-one relations.
        # (Note, too, that we clear the ordering here so as not to drag the
        # 'headline' field into the columns being used to determine uniqueness)
        d = {"reporter__first_name": "John", "reporter__last_name": "Smith"}
        qs = (
            Article.objects.filter(
                reporter=self.r,
            )
            .distinct()
            .order_by()
            .values("reporter__first_name", "reporter__last_name")
        )
        self.assertEqual([d], list(qs))

    def test_select_related(self):
        # Article.objects.select_related().dates() works properly when there
        # are multiple Articles with the same date but different foreign-key
        # objects (Reporters).
        r1 = Reporter.objects.create(
            first_name="Mike", last_name="Royko", email="royko@suntimes.com"
        )
        r2 = Reporter.objects.create(
            first_name="John", last_name="Kass", email="jkass@tribune.com"
        )
        Article.objects.create(
            headline="First", pub_date=datetime.date(1980, 4, 23), reporter=r1
        )
        Article.objects.create(
            headline="Second", pub_date=datetime.date(1980, 4, 23), reporter=r2
        )
        self.assertEqual(
            list(Article.objects.select_related().dates("pub_date", "day")),
            [datetime.date(1980, 4, 23), datetime.date(2005, 7, 27)],
        )
        self.assertEqual(
            list(Article.objects.select_related().dates("pub_date", "month")),
            [datetime.date(1980, 4, 1), datetime.date(2005, 7, 1)],
        )
        self.assertEqual(
            list(Article.objects.select_related().dates("pub_date", "year")),
            [datetime.date(1980, 1, 1), datetime.date(2005, 1, 1)],
        )

    def test_delete(self):
        new_article1 = self.r.article_set.create(
            headline="John's second story",
            pub_date=datetime.date(2005, 7, 29),
        )
        new_article2 = self.r2.article_set.create(
            headline="Paul's story",
            pub_date=datetime.date(2006, 1, 17),
        )
        new_article3 = Article.objects.create(
            headline="Third article",
            pub_date=datetime.date(2005, 7, 27),
            reporter_id=self.r.id,
        )
        new_article4 = Article.objects.create(
            headline="Fourth article",
            pub_date=datetime.date(2005, 7, 27),
            reporter_id=str(self.r.id),
        )
        # If you delete a reporter, their articles will be deleted.
        self.assertSequenceEqual(
            Article.objects.all(),
            [new_article4, new_article1, new_article2, new_article3, self.a],
        )
        self.assertSequenceEqual(
            Reporter.objects.order_by("first_name"),
            [self.r, self.r2],
        )
        self.r2.delete()
        self.assertSequenceEqual(
            Article.objects.all(),
            [new_article4, new_article1, new_article3, self.a],
        )
        self.assertSequenceEqual(Reporter.objects.order_by("first_name"), [self.r])
        # You can delete using a JOIN in the query.
        Reporter.objects.filter(article__headline__startswith="This").delete()
        self.assertSequenceEqual(Reporter.objects.all(), [])
        self.assertSequenceEqual(Article.objects.all(), [])

    def test_explicit_fk(self):
        # Create a new Article with get_or_create using an explicit value
        # for a ForeignKey.
        a2, created = Article.objects.get_or_create(
            headline="John's second test",
            pub_date=datetime.date(2011, 5, 7),
            reporter_id=self.r.id,
        )
        self.assertTrue(created)
        self.assertEqual(a2.reporter.id, self.r.id)

        # You can specify filters containing the explicit FK value.
        self.assertSequenceEqual(
            Article.objects.filter(reporter_id__exact=self.r.id),
            [a2, self.a],
        )

        # Create an Article by Paul for the same date.
        a3 = Article.objects.create(
            headline="Paul's commentary",
            pub_date=datetime.date(2011, 5, 7),
            reporter_id=self.r2.id,
        )
        self.assertEqual(a3.reporter.id, self.r2.id)

        # Get should respect explicit foreign keys as well.
        msg = "get() returned more than one Article -- it returned 2!"
        with self.assertRaisesMessage(MultipleObjectsReturned, msg):
            Article.objects.get(reporter_id=self.r.id)
        self.assertEqual(
            repr(a3),
            repr(
                Article.objects.get(
                    reporter_id=self.r2.id, pub_date=datetime.date(2011, 5, 7)
                )
            ),
        )

    def test_deepcopy_and_circular_references(self):
        # Regression for #12876 -- Model methods that include queries that
        # recursive don't cause recursion depth problems under deepcopy.
        self.r.cached_query = Article.objects.filter(reporter=self.r)
        self.assertEqual(repr(deepcopy(self.r)), "<Reporter: John Smith>")

    def test_manager_class_caching(self):
        r1 = Reporter.objects.create(first_name="Mike")
        r2 = Reporter.objects.create(first_name="John")

        # Same twice
        self.assertIs(r1.article_set.__class__, r1.article_set.__class__)

        # Same as each other
        self.assertIs(r1.article_set.__class__, r2.article_set.__class__)

    def test_create_relation_with_gettext_lazy(self):
        reporter = Reporter.objects.create(
            first_name="John", last_name="Smith", email="john.smith@example.com"
        )
        lazy = gettext_lazy("test")
        reporter.article_set.create(headline=lazy, pub_date=datetime.date(2011, 6, 10))
        notlazy = str(lazy)
        article = reporter.article_set.get()
        self.assertEqual(article.headline, notlazy)

    def test_values_list_exception(self):
        expected_message = (
            "Cannot resolve keyword 'notafield' into field. Choices are: %s"
        )
        reporter_fields = ", ".join(sorted(f.name for f in Reporter._meta.get_fields()))
        with self.assertRaisesMessage(FieldError, expected_message % reporter_fields):
            Article.objects.values_list("reporter__notafield")
        article_fields = ", ".join(
            ["EXTRA"] + sorted(f.name for f in Article._meta.get_fields())
        )
        with self.assertRaisesMessage(FieldError, expected_message % article_fields):
            Article.objects.extra(select={"EXTRA": "EXTRA_SELECT"}).values_list(
                "notafield"
            )

    def test_fk_assignment_and_related_object_cache(self):
        # Tests of ForeignKey assignment and the related-object cache (see
        # #6886).

        p = Parent.objects.create(name="Parent")
        c = Child.objects.create(name="Child", parent=p)

        # Look up the object again so that we get a "fresh" object.
        c = Child.objects.get(name="Child")
        p = c.parent

        # Accessing the related object again returns the exactly same object.
        self.assertIs(c.parent, p)

        # But if we kill the cache, we get a new object.
        del c._state.fields_cache["parent"]
        self.assertIsNot(c.parent, p)

        # Assigning a new object results in that object getting cached
        # immediately.
        p2 = Parent.objects.create(name="Parent 2")
        c.parent = p2
        self.assertIs(c.parent, p2)

        # Assigning None succeeds if field is null=True.
        p.bestchild = None
        self.assertIsNone(p.bestchild)

        # bestchild should still be None after saving.
        p.save()
        self.assertIsNone(p.bestchild)

        # bestchild should still be None after fetching the object again.
        p = Parent.objects.get(name="Parent")
        self.assertIsNone(p.bestchild)

        # Assigning None will not fail: Child.parent is null=False.
        setattr(c, "parent", None)

        # You also can't assign an object of the wrong type here
        msg = (
            'Cannot assign "<First: First object (1)>": "Child.parent" must '
            'be a "Parent" instance.'
        )
        with self.assertRaisesMessage(ValueError, msg):
            setattr(c, "parent", First(id=1, second=1))

        # You can assign None to Child.parent during object creation.
        Child(name="xyzzy", parent=None)

        # But when trying to save a Child with parent=None, the database will
        # raise IntegrityError.
        with self.assertRaises(IntegrityError), transaction.atomic():
            Child.objects.create(name="xyzzy", parent=None)

        # Creation using keyword argument should cache the related object.
        p = Parent.objects.get(name="Parent")
        c = Child(parent=p)
        self.assertIs(c.parent, p)

        # Creation using keyword argument and unsaved related instance (#8070).
        p = Parent()
        msg = (
            "save() prohibited to prevent data loss due to unsaved related object "
            "'parent'."
        )
        with self.assertRaisesMessage(ValueError, msg):
            Child.objects.create(parent=p)

        with self.assertRaisesMessage(ValueError, msg):
            ToFieldChild.objects.create(parent=p)

        # Creation using attname keyword argument and an id will cause the
        # related object to be fetched.
        p = Parent.objects.get(name="Parent")
        c = Child(parent_id=p.id)
        self.assertIsNot(c.parent, p)
        self.assertEqual(c.parent, p)

    def test_save_parent_after_assign(self):
        category = Category(name="cats")
        record = Record(category=category)
        category.save()
        record.save()
        category.name = "dogs"
        with self.assertNumQueries(0):
            self.assertEqual(category.id, record.category_id)
            self.assertEqual(category.name, record.category.name)

    def test_save_nullable_fk_after_parent(self):
        parent = Parent()
        child = ChildNullableParent(parent=parent)
        parent.save()
        child.save()
        child.refresh_from_db()
        self.assertEqual(child.parent, parent)

    def test_save_nullable_fk_after_parent_with_to_field(self):
        parent = Parent(name="jeff")
        child = ToFieldChild(parent=parent)
        parent.save()
        child.save()
        child.refresh_from_db()
        self.assertEqual(child.parent, parent)
        self.assertEqual(child.parent_id, parent.name)

    def test_save_fk_after_parent_with_non_numeric_pk_set_on_child(self):
        parent = ParentStringPrimaryKey()
        child = ChildStringPrimaryKeyParent(parent=parent)
        child.parent.name = "jeff"
        parent.save()
        child.save()
        child.refresh_from_db()
        self.assertEqual(child.parent, parent)
        self.assertEqual(child.parent_id, parent.name)

    def test_fk_to_bigautofield(self):
        ch = City.objects.create(name="Chicago")
        District.objects.create(city=ch, name="Far South")
        District.objects.create(city=ch, name="North")

        ny = City.objects.create(name="New York", id=2**33)
        District.objects.create(city=ny, name="Brooklyn")
        District.objects.create(city=ny, name="Manhattan")

    def test_fk_to_smallautofield(self):
        us = Country.objects.create(name="United States")
        City.objects.create(country=us, name="Chicago")
        City.objects.create(country=us, name="New York")

        uk = Country.objects.create(name="United Kingdom", id=2**11)
        City.objects.create(country=uk, name="London")
        City.objects.create(country=uk, name="Edinburgh")

    def test_multiple_foreignkeys(self):
        # Test of multiple ForeignKeys to the same model (bug #7125).
        c1 = Category.objects.create(name="First")
        c2 = Category.objects.create(name="Second")
        c3 = Category.objects.create(name="Third")
        r1 = Record.objects.create(category=c1)
        r2 = Record.objects.create(category=c1)
        r3 = Record.objects.create(category=c2)
        r4 = Record.objects.create(category=c2)
        r5 = Record.objects.create(category=c3)
        Relation.objects.create(left=r1, right=r2)
        Relation.objects.create(left=r3, right=r4)
        rel = Relation.objects.create(left=r1, right=r3)
        Relation.objects.create(left=r5, right=r2)
        Relation.objects.create(left=r3, right=r2)

        q1 = Relation.objects.filter(
            left__category__name__in=["First"], right__category__name__in=["Second"]
        )
        self.assertSequenceEqual(q1, [rel])

        q2 = Category.objects.filter(
            record__left_set__right__category__name="Second"
        ).order_by("name")
        self.assertSequenceEqual(q2, [c1, c2])

        p = Parent.objects.create(name="Parent")
        c = Child.objects.create(name="Child", parent=p)
        msg = 'Cannot assign "%r": "Child.parent" must be a "Parent" instance.' % c
        with self.assertRaisesMessage(ValueError, msg):
            Child.objects.create(name="Grandchild", parent=c)

    def test_fk_instantiation_outside_model(self):
        # Regression for #12190 -- Should be able to instantiate a FK outside
        # of a model, and interrogate its related field.
        cat = models.ForeignKey(Category, models.CASCADE)
        self.assertEqual("id", cat.remote_field.get_related_field().name)

    def test_relation_unsaved(self):
        Third.objects.create(name="Third 1")
        Third.objects.create(name="Third 2")
        th = Third(name="testing")
        # The object isn't saved and the relation cannot be used.
        msg = (
            "'Third' instance needs to have a primary key value before this "
            "relationship can be used."
        )
        with self.assertRaisesMessage(ValueError, msg):
            th.child_set.count()
        # The reverse foreign key manager can be created.
        self.assertEqual(th.child_set.model, Third)

        th.save()
        # Now the model is saved, so we will need to execute a query.
        with self.assertNumQueries(1):
            self.assertEqual(th.child_set.count(), 0)

    def test_related_object(self):
        public_school = School.objects.create(is_public=True)
        public_student = Student.objects.create(school=public_school)

        private_school = School.objects.create(is_public=False)
        private_student = Student.objects.create(school=private_school)

        # Only one school is available via all() due to the custom default
        # manager.
        self.assertSequenceEqual(School.objects.all(), [public_school])

        self.assertEqual(public_student.school, public_school)

        # Make sure the base manager is used so that a student can still access
        # its related school even if the default manager doesn't normally
        # allow it.
        self.assertEqual(private_student.school, private_school)

        School._meta.base_manager_name = "objects"
        School._meta._expire_cache()
        try:
            private_student = Student.objects.get(pk=private_student.pk)
            with self.assertRaises(School.DoesNotExist):
                private_student.school
        finally:
            School._meta.base_manager_name = None
            School._meta._expire_cache()

    def test_hasattr_related_object(self):
        # The exception raised on attribute access when a related object
        # doesn't exist should be an instance of a subclass of `AttributeError`
        # refs #21563
        self.assertFalse(hasattr(Article(), "reporter"))

    def test_create_after_prefetch(self):
        c = City.objects.create(name="Musical City")
        d1 = District.objects.create(name="Ladida", city=c)
        city = City.objects.prefetch_related("districts").get(id=c.id)
        self.assertSequenceEqual(city.districts.all(), [d1])
        d2 = city.districts.create(name="Goa")
        self.assertSequenceEqual(city.districts.all(), [d1, d2])

    def test_clear_after_prefetch(self):
        c = City.objects.create(name="Musical City")
        d = District.objects.create(name="Ladida", city=c)
        city = City.objects.prefetch_related("districts").get(id=c.id)
        self.assertSequenceEqual(city.districts.all(), [d])
        city.districts.clear()
        self.assertSequenceEqual(city.districts.all(), [])

    def test_remove_after_prefetch(self):
        c = City.objects.create(name="Musical City")
        d = District.objects.create(name="Ladida", city=c)
        city = City.objects.prefetch_related("districts").get(id=c.id)
        self.assertSequenceEqual(city.districts.all(), [d])
        city.districts.remove(d)
        self.assertSequenceEqual(city.districts.all(), [])

    def test_add_after_prefetch(self):
        c = City.objects.create(name="Musical City")
        District.objects.create(name="Ladida", city=c)
        d2 = District.objects.create(name="Ladidu")
        city = City.objects.prefetch_related("districts").get(id=c.id)
        self.assertEqual(city.districts.count(), 1)
        city.districts.add(d2)
        self.assertEqual(city.districts.count(), 2)

    def test_set_after_prefetch(self):
        c = City.objects.create(name="Musical City")
        District.objects.create(name="Ladida", city=c)
        d2 = District.objects.create(name="Ladidu")
        city = City.objects.prefetch_related("districts").get(id=c.id)
        self.assertEqual(city.districts.count(), 1)
        city.districts.set([d2])
        self.assertSequenceEqual(city.districts.all(), [d2])

    def test_add_then_remove_after_prefetch(self):
        c = City.objects.create(name="Musical City")
        District.objects.create(name="Ladida", city=c)
        d2 = District.objects.create(name="Ladidu")
        city = City.objects.prefetch_related("districts").get(id=c.id)
        self.assertEqual(city.districts.count(), 1)
        city.districts.add(d2)
        self.assertEqual(city.districts.count(), 2)
        city.districts.remove(d2)
        self.assertEqual(city.districts.count(), 1)

    def test_cached_relation_invalidated_on_save(self):
        """
        Model.save() invalidates stale ForeignKey relations after a primary key
        assignment.
        """
        self.assertEqual(self.a.reporter, self.r)  # caches a.reporter
        self.a.reporter_id = self.r2.pk
        self.a.save()
        self.assertEqual(self.a.reporter, self.r2)

    def test_cached_foreign_key_with_to_field_not_cleared_by_save(self):
        parent = Parent.objects.create(name="a")
        child = ToFieldChild.objects.create(parent=parent)
        with self.assertNumQueries(0):
            self.assertIs(child.parent, parent)

    def test_reverse_foreign_key_instance_to_field_caching(self):
        parent = Parent.objects.create(name="a")
        ToFieldChild.objects.create(parent=parent)
        child = parent.to_field_children.get()
        with self.assertNumQueries(0):
            self.assertIs(child.parent, parent)

    def test_add_remove_set_by_pk_raises(self):
        usa = Country.objects.create(name="United States")
        chicago = City.objects.create(name="Chicago")
        msg = "'City' instance expected, got %s" % chicago.pk
        with self.assertRaisesMessage(TypeError, msg):
            usa.cities.add(chicago.pk)
        with self.assertRaisesMessage(TypeError, msg):
            usa.cities.remove(chicago.pk)
        with self.assertRaisesMessage(TypeError, msg):
            usa.cities.set([chicago.pk])

    def test_get_prefetch_querysets_invalid_querysets_length(self):
        City.objects.create(name="Chicago")
        cities = City.objects.all()
        msg = (
            "querysets argument of get_prefetch_querysets() should have a length of 1."
        )
        with self.assertRaisesMessage(ValueError, msg):
            City.country.get_prefetch_querysets(
                instances=cities,
                querysets=[Country.objects.all(), Country.objects.all()],
            )

    def test_get_prefetch_querysets_reverse_invalid_querysets_length(self):
        usa = Country.objects.create(name="United States")
        City.objects.create(name="Chicago")
        countries = Country.objects.all()
        msg = (
            "querysets argument of get_prefetch_querysets() should have a length of 1."
        )
        with self.assertRaisesMessage(ValueError, msg):
            usa.cities.get_prefetch_querysets(
                instances=countries,
                querysets=[City.objects.all(), City.objects.all()],
            )

    def test_fetch_mode_fetch_peers_forward(self):
        Article.objects.create(
            headline="This is another test",
            pub_date=datetime.date(2005, 7, 27),
            reporter=self.r2,
        )
        a1, a2 = Article.objects.fetch_mode(FETCH_PEERS)
        with self.assertNumQueries(1):
            a1.reporter
        with self.assertNumQueries(0):
            a2.reporter

    def test_fetch_mode_raise_forward(self):
        a = Article.objects.fetch_mode(RAISE).get(pk=self.a.pk)
        msg = "Fetching of Article.reporter blocked."
        with self.assertRaisesMessage(FieldFetchBlocked, msg) as cm:
            a.reporter
        self.assertIsNone(cm.exception.__cause__)
        self.assertTrue(cm.exception.__suppress_context__)

    def test_fetch_mode_copied_forward_fetching_one(self):
        a1 = Article.objects.fetch_mode(FETCH_PEERS).get()
        self.assertEqual(a1._state.fetch_mode, FETCH_PEERS)
        self.assertEqual(
            a1.reporter._state.fetch_mode,
            FETCH_PEERS,
        )

    def test_fetch_mode_copied_forward_fetching_many(self):
        Article.objects.create(
            headline="This is another test",
            pub_date=datetime.date(2005, 7, 27),
            reporter=self.r2,
        )
        a1, a2 = Article.objects.fetch_mode(FETCH_PEERS)
        self.assertEqual(a1._state.fetch_mode, FETCH_PEERS)
        self.assertEqual(
            a1.reporter._state.fetch_mode,
            FETCH_PEERS,
        )

    def test_fetch_mode_copied_reverse_fetching_one(self):
        r1 = Reporter.objects.fetch_mode(FETCH_PEERS).get(pk=self.r.pk)
        self.assertEqual(r1._state.fetch_mode, FETCH_PEERS)
        article = r1.article_set.get()
        self.assertEqual(
            article._state.fetch_mode,
            FETCH_PEERS,
        )

    def test_fetch_mode_copied_reverse_fetching_many(self):
        Article.objects.create(
            headline="This is another test",
            pub_date=datetime.date(2005, 7, 27),
            reporter=self.r2,
        )
        r1, r2 = Reporter.objects.fetch_mode(FETCH_PEERS)
        self.assertEqual(r1._state.fetch_mode, FETCH_PEERS)
        a1 = r1.article_set.get()
        self.assertEqual(
            a1._state.fetch_mode,
            FETCH_PEERS,
        )
        a2 = r2.article_set.get()
        self.assertEqual(
            a2._state.fetch_mode,
            FETCH_PEERS,
        )