Refs #18081 -- Asserted db constraints are created for fk to proxy models.

        else:

            self.fail("No FK constraint for author_id found")

    @skipUnlessDBFeature('supports_foreign_keys')

    def test_fk_to_proxy(self):

        "Tests that creating a FK to a proxy model creates database constraints."

        class AuthorProxy(Author):

            class Meta:

                app_label = 'schema'

                apps = new_apps

                proxy = True

        class AuthorRef(Model):

            author = ForeignKey(AuthorProxy, on_delete=CASCADE)

            class Meta:

                app_label = 'schema'

                apps = new_apps

        self.local_models = [AuthorProxy, AuthorRef]

        # Create the table

        with connection.schema_editor() as editor:

            editor.create_model(Author)

            editor.create_model(AuthorRef)

        constraints = self.get_constraints(AuthorRef._meta.db_table)

        for details in constraints.values():

            if details['columns'] == ['author_id'] and details['foreign_key']:

                self.assertEqual(details['foreign_key'], ('schema_author', 'id'))

                break

        else:

            self.fail('No FK constraint for author_id found')

    @skipUnlessDBFeature('supports_foreign_keys')

    def test_fk_db_constraint(self):

        "Tests that the db_constraint parameter is respected"