django/tests/many_to_one/tests.py

import datetime
from copy import deepcopy

from django.core.exceptions import FieldError, MultipleObjectsReturned
from django.db import models, transaction
from django.test import TestCase
from django.utils import six
from django.utils.translation import ugettext_lazy

from .models import (
    Article, Category, Child, First, Parent, Record, Relation, Reporter,
    School, Student, Third, ToFieldChild,
)


class ManyToOneTests(TestCase):
    def setUp(self):
        # Create a few Reporters.
        self.r = Reporter(first_name='John', last_name='Smith', email='john@example.com')
        self.r.save()
        self.r2 = Reporter(first_name='Paul', last_name='Jones', email='paul@example.com')
        self.r2.save()
        # Create an Article.
        self.a = Article(id=None, headline="This is a test",
                         pub_date=datetime.date(2005, 7, 27), reporter=self.r)
        self.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)
        # These are strings instead of unicode strings because that's what was used in
        # the creation of this reporter (and we haven't refreshed the data from the
        # database, which always returns unicode strings).
        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(id=None, 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(id=None, 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))
        self.r.article_set.add(new_article2)
        self.assertEqual(new_article2.reporter.id, self.r.id)
        self.assertQuerysetEqual(self.r.article_set.all(),
            [
                "<Article: John's second story>",
                "<Article: Paul's story>",
                "<Article: This is a test>",
            ])

        # 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.assertQuerysetEqual(self.r2.article_set.all(), ["<Article: Paul's story>"])

        # Adding an object of the wrong type raises TypeError.
        with transaction.atomic():
            with six.assertRaisesRegex(self, TypeError,
                                       "'Article' instance expected, got <Reporter.*"):
                self.r.article_set.add(self.r2)
        self.assertQuerysetEqual(self.r.article_set.all(),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])

    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.assertQuerysetEqual(self.r.article_set.all(), [
            "<Article: John's second story>",
            "<Article: Paul's story>",
            "<Article: This is a test>",
        ])
        self.assertQuerysetEqual(self.r2.article_set.all(), [])

        # Set the article back again.
        self.r2.article_set.set([new_article, new_article2])
        self.assertQuerysetEqual(self.r.article_set.all(), ["<Article: This is a test>"])
        self.assertQuerysetEqual(self.r2.article_set.all(),
            [
                "<Article: John's second story>",
                "<Article: Paul's story>",
            ])

        # Funny case - because the ForeignKey cannot be null,
        # existing members of the set must remain.
        self.r.article_set.set([new_article])
        self.assertQuerysetEqual(self.r.article_set.all(),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(self.r2.article_set.all(), ["<Article: Paul's story>"])

    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.assertQuerysetEqual(self.r.article_set.all(), [
            "<Article: John's second story>",
            "<Article: Paul's story>",
            "<Article: This is a test>",
        ])
        self.assertQuerysetEqual(self.r2.article_set.all(), [])

        # Set the article back again using set descriptor.
        self.r2.article_set = [new_article, new_article2]
        self.assertQuerysetEqual(self.r.article_set.all(), ["<Article: This is a test>"])
        self.assertQuerysetEqual(self.r2.article_set.all(),
            [
                "<Article: John's second story>",
                "<Article: Paul's story>",
            ])

        # Funny case - assignment notation can only go so far; because the
        # ForeignKey cannot be null, existing members of the set must remain.
        self.r.article_set = [new_article]
        self.assertQuerysetEqual(self.r.article_set.all(),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(self.r2.article_set.all(), ["<Article: Paul's story>"])
        # 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_unsaved_check_override(self):
        """
        #24495 - Assigning an unsaved object to a ForeignKey
        should be allowed when the allow_unsaved_instance_assignment
        attribute has been set to True.
        """
        class UnsavedForeignKey(models.ForeignKey):
            # A ForeignKey which can point to an unsaved object
            allow_unsaved_instance_assignment = True

        class Band(models.Model):
            name = models.CharField(max_length=50)

        class BandMember(models.Model):
            band = UnsavedForeignKey(Band)
            first_name = models.CharField(max_length=50)
            last_name = models.CharField(max_length=50)

        beatles = Band(name='The Beatles')
        john = BandMember(first_name='John', last_name='Lennon')
        # This should not raise an exception as the ForeignKey between member
        # and band has allow_unsaved_instance_assignment=True.
        john.band = beatles
        self.assertEqual(john.band, beatles)

    def test_selects(self):
        self.r.article_set.create(headline="John's second story",
                                  pub_date=datetime.date(2005, 7, 29))
        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.assertQuerysetEqual(self.r.article_set.all(), [
            "<Article: John's second story>",
            "<Article: This is a test>",
        ])
        self.assertQuerysetEqual(self.r.article_set.filter(headline__startswith='This'),
                                 ["<Article: This is a test>"])
        self.assertEqual(self.r.article_set.count(), 2)
        self.assertEqual(self.r2.article_set.count(), 1)
        # Get articles by id
        self.assertQuerysetEqual(Article.objects.filter(id__exact=self.a.id),
                                 ["<Article: This is a test>"])
        self.assertQuerysetEqual(Article.objects.filter(pk=self.a.id),
                                 ["<Article: This is a test>"])
        # Query on an article property
        self.assertQuerysetEqual(Article.objects.filter(headline__startswith='This'),
                                 ["<Article: This is a test>"])
        # 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.assertQuerysetEqual(Article.objects.filter(reporter__first_name__exact='John'),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        # Check that implied __exact also works
        self.assertQuerysetEqual(Article.objects.filter(reporter__first_name='John'),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        # Query twice over the related field.
        self.assertQuerysetEqual(
            Article.objects.filter(reporter__first_name__exact='John',
                                   reporter__last_name__exact='Smith'),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        # 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.assertQuerysetEqual(
            Article.objects.filter(reporter__first_name__exact='John').extra(
                where=["many_to_one_reporter.last_name='Smith'"]),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        # ... and should work fine with the unicode 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'])),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        # Find all Articles for a Reporter.
        # Use direct ID check, pk check, and object comparison
        self.assertQuerysetEqual(
            Article.objects.filter(reporter__id__exact=self.r.id),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(
            Article.objects.filter(reporter__pk=self.r.id),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(
            Article.objects.filter(reporter=self.r.id),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(
            Article.objects.filter(reporter=self.r),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(
            Article.objects.filter(reporter__in=[self.r.id, self.r2.id]).distinct(),
            [
                "<Article: John's second story>",
                "<Article: Paul's story>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(
            Article.objects.filter(reporter__in=[self.r, self.r2]).distinct(),
            [
                "<Article: John's second story>",
                "<Article: Paul's story>",
                "<Article: This is a test>",
            ])
        # 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.assertQuerysetEqual(
            Article.objects.filter(
                reporter__in=Reporter.objects.filter(first_name='John').values('pk').query
            ).distinct(),
            [
                "<Article: John's second story>",
                "<Article: This is a test>",
            ])

    def test_reverse_selects(self):
        a3 = Article.objects.create(id=None, headline="Third article",
                                    pub_date=datetime.date(2005, 7, 27), reporter_id=self.r.id)
        Article.objects.create(id=None, headline="Fourth article",
                               pub_date=datetime.date(2005, 7, 27), reporter_id=str(self.r.id))
        # Reporters can be queried
        self.assertQuerysetEqual(Reporter.objects.filter(id__exact=self.r.id),
                                 ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(Reporter.objects.filter(pk=self.r.id),
                                 ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(Reporter.objects.filter(first_name__startswith='John'),
                                 ["<Reporter: John Smith>"])
        # Reporters can query in opposite direction of ForeignKey definition
        self.assertQuerysetEqual(Reporter.objects.filter(article__id__exact=self.a.id),
                                 ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(Reporter.objects.filter(article__pk=self.a.id),
                                 ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(Reporter.objects.filter(article=self.a.id),
                                 ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(Reporter.objects.filter(article=self.a),
                                 ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__in=[self.a.id, a3.id]).distinct(),
            ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__in=[self.a.id, a3]).distinct(),
            ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__in=[self.a, a3]).distinct(),
            ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__headline__startswith='T'),
            ["<Reporter: John Smith>", "<Reporter: John Smith>"],
            ordered=False
        )
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__headline__startswith='T').distinct(),
            ["<Reporter: 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.assertQuerysetEqual(
            Reporter.objects.filter(article__reporter__first_name__startswith='John'),
            [
                "<Reporter: John Smith>",
                "<Reporter: John Smith>",
                "<Reporter: John Smith>",
            ],
            ordered=False
        )
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__reporter__first_name__startswith='John').distinct(),
            ["<Reporter: John Smith>"])
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__reporter__exact=self.r).distinct(),
            ["<Reporter: John Smith>"])

        # Check that implied __exact also works.
        self.assertQuerysetEqual(
            Reporter.objects.filter(article__reporter=self.r).distinct(),
            ["<Reporter: 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'}
        self.assertEqual([d],
            list(Article.objects.filter(reporter=self.r).distinct().order_by()
                 .values('reporter__first_name', 'reporter__last_name')))

    def test_select_related(self):
        # Check that 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):
        self.r.article_set.create(headline="John's second story",
                                  pub_date=datetime.date(2005, 7, 29))
        self.r2.article_set.create(headline="Paul's story",
                                   pub_date=datetime.date(2006, 1, 17))
        Article.objects.create(id=None, headline="Third article",
                               pub_date=datetime.date(2005, 7, 27), reporter_id=self.r.id)
        Article.objects.create(id=None, headline="Fourth article",
                               pub_date=datetime.date(2005, 7, 27), reporter_id=str(self.r.id))
        # If you delete a reporter, his articles will be deleted.
        self.assertQuerysetEqual(Article.objects.all(),
            [
                "<Article: Fourth article>",
                "<Article: John's second story>",
                "<Article: Paul's story>",
                "<Article: Third article>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(Reporter.objects.order_by('first_name'),
            [
                "<Reporter: John Smith>",
                "<Reporter: Paul Jones>",
            ])
        self.r2.delete()
        self.assertQuerysetEqual(Article.objects.all(),
            [
                "<Article: Fourth article>",
                "<Article: John's second story>",
                "<Article: Third article>",
                "<Article: This is a test>",
            ])
        self.assertQuerysetEqual(Reporter.objects.order_by('first_name'),
                                 ["<Reporter: John Smith>"])
        # You can delete using a JOIN in the query.
        Reporter.objects.filter(article__headline__startswith='This').delete()
        self.assertQuerysetEqual(Reporter.objects.all(), [])
        self.assertQuerysetEqual(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(id=None,
                                                    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.assertQuerysetEqual(
            Article.objects.filter(reporter_id__exact=self.r.id),
            [
                "<Article: John's second test>",
                "<Article: This is a test>",
            ])

        # Create an Article by Paul for the same date.
        a3 = Article.objects.create(id=None, 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.
        self.assertRaises(MultipleObjectsReturned,
                          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_ugettext_lazy(self):
        reporter = Reporter.objects.create(first_name='John',
                                           last_name='Smith',
                                           email='john.smith@example.com')
        lazy = ugettext_lazy('test')
        reporter.article_set.create(headline=lazy,
                                    pub_date=datetime.date(2011, 6, 10))
        notlazy = six.text_type(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"

        self.assertRaisesMessage(FieldError,
                                 expected_message % ', '.join(sorted(f.name for f in Reporter._meta.get_fields())),
                                 Article.objects.values_list,
                                 'reporter__notafield')
        self.assertRaisesMessage(FieldError,
                                 expected_message % ', '.join(['EXTRA'] + sorted(f.name for f in Article._meta.get_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._parent_cache
        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 fails: Child.parent is null=False.
        self.assertRaises(ValueError, setattr, c, "parent", None)

        # You also can't assign an object of the wrong type here
        self.assertRaises(ValueError, setattr, c, "parent", First(id=1, second=1))

        # Nor can you explicitly assign None to Child.parent during object
        # creation (regression for #9649).
        self.assertRaises(ValueError, Child, name='xyzzy', parent=None)
        self.assertRaises(ValueError, 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()
        with self.assertRaisesMessage(ValueError,
                'Cannot assign "%r": "%s" instance isn\'t saved in the database.'
                % (p, Child.parent.field.remote_field.model._meta.object_name)):
            Child(parent=p)

        with self.assertRaisesMessage(ValueError,
                'Cannot assign "%r": "%s" instance isn\'t saved in the database.'
                % (p, Child.parent.field.remote_field.model._meta.object_name)):
            ToFieldChild(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_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)
        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.assertQuerysetEqual(q1, ["<Relation: First - Second>"])

        q2 = Category.objects.filter(record__left_set__right__category__name='Second').order_by('name')
        self.assertQuerysetEqual(q2, ["<Category: First>", "<Category: Second>"])

        p = Parent.objects.create(name="Parent")
        c = Child.objects.create(name="Child", parent=p)
        self.assertRaises(ValueError, 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)
        self.assertEqual('id', cat.remote_field.get_related_field().name)

    def test_relation_unsaved(self):
        # Test that the <field>_set manager does not join on Null value fields (#17541)
        Third.objects.create(name='Third 1')
        Third.objects.create(name='Third 2')
        th = Third(name="testing")
        # The object isn't saved an thus the relation field is null - we won't even
        # execute a query in this case.
        with self.assertNumQueries(0):
            self.assertEqual(th.child_set.count(), 0)
        th.save()
        # Now the model is saved, so we will need to execute an 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.assertQuerysetEqual(
            School.objects.all(),
            ["<School: School object>"]
        )

        self.assertEqual(public_student.school, public_school)

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

        # If the manager is marked "use_for_related_fields", it'll get used instead
        # of the "bare" queryset. Usually you'd define this as a property on the class,
        # but this approximates that in a way that's easier in tests.
        School.objects.use_for_related_fields = True
        try:
            private_student = Student.objects.get(pk=private_student.pk)
            self.assertRaises(School.DoesNotExist, lambda: private_student.school)
        finally:
            School.objects.use_for_related_fields = False

    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'))