django1/tests/multiple_database/tests.py

import datetime
import pickle
from io import StringIO
from operator import attrgetter
from unittest.mock import Mock

from django.contrib.auth.models import User
from django.contrib.contenttypes.models import ContentType
from django.core import management
from django.db import DEFAULT_DB_ALIAS, connections, router, transaction
from django.db.models import signals
from django.db.utils import ConnectionRouter
from django.test import SimpleTestCase, TestCase, override_settings

from .models import Book, Person, Pet, Review, UserProfile
from .routers import AuthRouter, TestRouter, WriteRouter


class QueryTestCase(TestCase):
    databases = {'default', 'other'}

    def test_db_selection(self):
        "Querysets will use the default database by default"
        self.assertEqual(Book.objects.db, DEFAULT_DB_ALIAS)
        self.assertEqual(Book.objects.all().db, DEFAULT_DB_ALIAS)

        self.assertEqual(Book.objects.using('other').db, 'other')

        self.assertEqual(Book.objects.db_manager('other').db, 'other')
        self.assertEqual(Book.objects.db_manager('other').all().db, 'other')

    def test_default_creation(self):
        "Objects created on the default database don't leak onto other databases"
        # Create a book on the default database using create()
        Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))

        # Create a book on the default database using a save
        dive = Book()
        dive.title = "Dive into Python"
        dive.published = datetime.date(2009, 5, 4)
        dive.save()

        # Book exists on the default database, but not on other database
        try:
            Book.objects.get(title="Pro Django")
            Book.objects.using('default').get(title="Pro Django")
        except Book.DoesNotExist:
            self.fail('"Pro Django" should exist on default database')

        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('other').get(title="Pro Django")

        try:
            Book.objects.get(title="Dive into Python")
            Book.objects.using('default').get(title="Dive into Python")
        except Book.DoesNotExist:
            self.fail('"Dive into Python" should exist on default database')

        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('other').get(title="Dive into Python")

    def test_other_creation(self):
        "Objects created on another database don't leak onto the default database"
        # Create a book on the second database
        Book.objects.using('other').create(title="Pro Django",
                                           published=datetime.date(2008, 12, 16))

        # Create a book on the default database using a save
        dive = Book()
        dive.title = "Dive into Python"
        dive.published = datetime.date(2009, 5, 4)
        dive.save(using='other')

        # Book exists on the default database, but not on other database
        try:
            Book.objects.using('other').get(title="Pro Django")
        except Book.DoesNotExist:
            self.fail('"Pro Django" should exist on other database')

        with self.assertRaises(Book.DoesNotExist):
            Book.objects.get(title="Pro Django")
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(title="Pro Django")

        try:
            Book.objects.using('other').get(title="Dive into Python")
        except Book.DoesNotExist:
            self.fail('"Dive into Python" should exist on other database')

        with self.assertRaises(Book.DoesNotExist):
            Book.objects.get(title="Dive into Python")
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(title="Dive into Python")

    def test_refresh(self):
        dive = Book(title="Dive into Python", published=datetime.date(2009, 5, 4))
        dive.save(using='other')
        dive2 = Book.objects.using('other').get()
        dive2.title = "Dive into Python (on default)"
        dive2.save(using='default')
        dive.refresh_from_db()
        self.assertEqual(dive.title, "Dive into Python")
        dive.refresh_from_db(using='default')
        self.assertEqual(dive.title, "Dive into Python (on default)")
        self.assertEqual(dive._state.db, "default")

    def test_refresh_router_instance_hint(self):
        router = Mock()
        router.db_for_read.return_value = None
        book = Book.objects.create(title='Dive Into Python', published=datetime.date(1957, 10, 12))
        with self.settings(DATABASE_ROUTERS=[router]):
            book.refresh_from_db()
        router.db_for_read.assert_called_once_with(Book, instance=book)

    def test_basic_queries(self):
        "Queries are constrained to a single database"
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        dive = Book.objects.using('other').get(published=datetime.date(2009, 5, 4))
        self.assertEqual(dive.title, "Dive into Python")
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(published=datetime.date(2009, 5, 4))

        dive = Book.objects.using('other').get(title__icontains="dive")
        self.assertEqual(dive.title, "Dive into Python")
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(title__icontains="dive")

        dive = Book.objects.using('other').get(title__iexact="dive INTO python")
        self.assertEqual(dive.title, "Dive into Python")
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(title__iexact="dive INTO python")

        dive = Book.objects.using('other').get(published__year=2009)
        self.assertEqual(dive.title, "Dive into Python")
        self.assertEqual(dive.published, datetime.date(2009, 5, 4))
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(published__year=2009)

        years = Book.objects.using('other').dates('published', 'year')
        self.assertEqual([o.year for o in years], [2009])
        years = Book.objects.using('default').dates('published', 'year')
        self.assertEqual([o.year for o in years], [])

        months = Book.objects.using('other').dates('published', 'month')
        self.assertEqual([o.month for o in months], [5])
        months = Book.objects.using('default').dates('published', 'month')
        self.assertEqual([o.month for o in months], [])

    def test_m2m_separation(self):
        "M2M fields are constrained to a single database"
        # Create a book and author on the default database
        pro = Book.objects.create(title="Pro Django",
                                  published=datetime.date(2008, 12, 16))

        marty = Person.objects.create(name="Marty Alchin")

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        mark = Person.objects.using('other').create(name="Mark Pilgrim")

        # Save the author relations
        pro.authors.set([marty])
        dive.authors.set([mark])

        # Inspect the m2m tables directly.
        # There should be 1 entry in each database
        self.assertEqual(Book.authors.through.objects.using('default').count(), 1)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 1)

        # Queries work across m2m joins
        self.assertEqual(
            list(Book.objects.using('default').filter(authors__name='Marty Alchin').values_list('title', flat=True)),
            ['Pro Django']
        )
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Marty Alchin').values_list('title', flat=True)),
            []
        )

        self.assertEqual(
            list(Book.objects.using('default').filter(authors__name='Mark Pilgrim').values_list('title', flat=True)),
            []
        )
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Mark Pilgrim').values_list('title', flat=True)),
            ['Dive into Python']
        )

        # Reget the objects to clear caches
        dive = Book.objects.using('other').get(title="Dive into Python")
        mark = Person.objects.using('other').get(name="Mark Pilgrim")

        # Retrieve related object by descriptor. Related objects should be database-bound
        self.assertEqual(list(dive.authors.all().values_list('name', flat=True)), ['Mark Pilgrim'])

        self.assertEqual(list(mark.book_set.all().values_list('title', flat=True)), ['Dive into Python'])

    def test_m2m_forward_operations(self):
        "M2M forward manipulations are all constrained to a single DB"
        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        mark = Person.objects.using('other').create(name="Mark Pilgrim")

        # Save the author relations
        dive.authors.set([mark])

        # Add a second author
        john = Person.objects.using('other').create(name="John Smith")
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='John Smith').values_list('title', flat=True)),
            []
        )

        dive.authors.add(john)
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Mark Pilgrim').values_list('title', flat=True)),
            ['Dive into Python']
        )
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='John Smith').values_list('title', flat=True)),
            ['Dive into Python']
        )

        # Remove the second author
        dive.authors.remove(john)
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Mark Pilgrim').values_list('title', flat=True)),
            ['Dive into Python']
        )
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='John Smith').values_list('title', flat=True)),
            []
        )

        # Clear all authors
        dive.authors.clear()
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Mark Pilgrim').values_list('title', flat=True)),
            []
        )
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='John Smith').values_list('title', flat=True)),
            []
        )

        # Create an author through the m2m interface
        dive.authors.create(name='Jane Brown')
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Mark Pilgrim').values_list('title', flat=True)),
            []
        )
        self.assertEqual(
            list(Book.objects.using('other').filter(authors__name='Jane Brown').values_list('title', flat=True)),
            ['Dive into Python']
        )

    def test_m2m_reverse_operations(self):
        "M2M reverse manipulations are all constrained to a single DB"
        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        mark = Person.objects.using('other').create(name="Mark Pilgrim")

        # Save the author relations
        dive.authors.set([mark])

        # Create a second book on the other database
        grease = Book.objects.using('other').create(title="Greasemonkey Hacks", published=datetime.date(2005, 11, 1))

        # Add a books to the m2m
        mark.book_set.add(grease)
        self.assertEqual(
            list(Person.objects.using('other').filter(book__title='Dive into Python').values_list('name', flat=True)),
            ['Mark Pilgrim']
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(book__title='Greasemonkey Hacks').values_list('name', flat=True)
            ),
            ['Mark Pilgrim']
        )

        # Remove a book from the m2m
        mark.book_set.remove(grease)
        self.assertEqual(
            list(Person.objects.using('other').filter(book__title='Dive into Python').values_list('name', flat=True)),
            ['Mark Pilgrim']
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(book__title='Greasemonkey Hacks').values_list('name', flat=True)
            ),
            []
        )

        # Clear the books associated with mark
        mark.book_set.clear()
        self.assertEqual(
            list(Person.objects.using('other').filter(book__title='Dive into Python').values_list('name', flat=True)),
            []
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(book__title='Greasemonkey Hacks').values_list('name', flat=True)
            ),
            []
        )

        # Create a book through the m2m interface
        mark.book_set.create(title="Dive into HTML5", published=datetime.date(2020, 1, 1))
        self.assertEqual(
            list(Person.objects.using('other').filter(book__title='Dive into Python').values_list('name', flat=True)),
            []
        )
        self.assertEqual(
            list(Person.objects.using('other').filter(book__title='Dive into HTML5').values_list('name', flat=True)),
            ['Mark Pilgrim']
        )

    def test_m2m_cross_database_protection(self):
        "Operations that involve sharing M2M objects across databases raise an error"
        # Create a book and author on the default database
        pro = Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))

        marty = Person.objects.create(name="Marty Alchin")

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        mark = Person.objects.using('other').create(name="Mark Pilgrim")
        # Set a foreign key set with an object from a different database
        msg = (
            'Cannot assign "<Person: Marty Alchin>": the current database '
            'router prevents this relation.'
        )
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='default'):
                marty.edited.set([pro, dive])

        # Add to an m2m with an object from a different database
        msg = (
            'Cannot add "<Book: Dive into Python>": instance is on '
            'database "default", value is on database "other"'
        )
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='default'):
                marty.book_set.add(dive)

        # Set a m2m with an object from a different database
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='default'):
                marty.book_set.set([pro, dive])

        # Add to a reverse m2m with an object from a different database
        msg = (
            'Cannot add "<Person: Marty Alchin>": instance is on '
            'database "other", value is on database "default"'
        )
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='other'):
                dive.authors.add(marty)

        # Set a reverse m2m with an object from a different database
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='other'):
                dive.authors.set([mark, marty])

    def test_m2m_deletion(self):
        "Cascaded deletions of m2m relations issue queries on the right database"
        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        mark = Person.objects.using('other').create(name="Mark Pilgrim")
        dive.authors.set([mark])

        # Check the initial state
        self.assertEqual(Person.objects.using('default').count(), 0)
        self.assertEqual(Book.objects.using('default').count(), 0)
        self.assertEqual(Book.authors.through.objects.using('default').count(), 0)

        self.assertEqual(Person.objects.using('other').count(), 1)
        self.assertEqual(Book.objects.using('other').count(), 1)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 1)

        # Delete the object on the other database
        dive.delete(using='other')

        self.assertEqual(Person.objects.using('default').count(), 0)
        self.assertEqual(Book.objects.using('default').count(), 0)
        self.assertEqual(Book.authors.through.objects.using('default').count(), 0)

        # The person still exists ...
        self.assertEqual(Person.objects.using('other').count(), 1)
        # ... but the book has been deleted
        self.assertEqual(Book.objects.using('other').count(), 0)
        # ... and the relationship object has also been deleted.
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

        # Now try deletion in the reverse direction. Set up the relation again
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        dive.authors.set([mark])

        # Check the initial state
        self.assertEqual(Person.objects.using('default').count(), 0)
        self.assertEqual(Book.objects.using('default').count(), 0)
        self.assertEqual(Book.authors.through.objects.using('default').count(), 0)

        self.assertEqual(Person.objects.using('other').count(), 1)
        self.assertEqual(Book.objects.using('other').count(), 1)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 1)

        # Delete the object on the other database
        mark.delete(using='other')

        self.assertEqual(Person.objects.using('default').count(), 0)
        self.assertEqual(Book.objects.using('default').count(), 0)
        self.assertEqual(Book.authors.through.objects.using('default').count(), 0)

        # The person has been deleted ...
        self.assertEqual(Person.objects.using('other').count(), 0)
        # ... but the book still exists
        self.assertEqual(Book.objects.using('other').count(), 1)
        # ... and the relationship object has been deleted.
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

    def test_foreign_key_separation(self):
        "FK fields are constrained to a single database"
        # Create a book and author on the default database
        pro = Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))

        george = Person.objects.create(name="George Vilches")

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        chris = Person.objects.using('other').create(name="Chris Mills")

        # Save the author's favorite books
        pro.editor = george
        pro.save()

        dive.editor = chris
        dive.save()

        pro = Book.objects.using('default').get(title="Pro Django")
        self.assertEqual(pro.editor.name, "George Vilches")

        dive = Book.objects.using('other').get(title="Dive into Python")
        self.assertEqual(dive.editor.name, "Chris Mills")

        # Queries work across foreign key joins
        self.assertEqual(
            list(Person.objects.using('default').filter(edited__title='Pro Django').values_list('name', flat=True)),
            ['George Vilches']
        )
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Pro Django').values_list('name', flat=True)),
            []
        )

        self.assertEqual(
            list(
                Person.objects.using('default').filter(edited__title='Dive into Python').values_list('name', flat=True)
            ),
            []
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(edited__title='Dive into Python').values_list('name', flat=True)
            ),
            ['Chris Mills']
        )

        # Reget the objects to clear caches
        chris = Person.objects.using('other').get(name="Chris Mills")
        dive = Book.objects.using('other').get(title="Dive into Python")

        # Retrieve related object by descriptor. Related objects should be database-bound
        self.assertEqual(list(chris.edited.values_list('title', flat=True)), ['Dive into Python'])

    def test_foreign_key_reverse_operations(self):
        "FK reverse manipulations are all constrained to a single DB"
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        chris = Person.objects.using('other').create(name="Chris Mills")

        # Save the author relations
        dive.editor = chris
        dive.save()

        # Add a second book edited by chris
        html5 = Book.objects.using('other').create(title="Dive into HTML5", published=datetime.date(2010, 3, 15))
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Dive into HTML5').values_list('name', flat=True)),
            []
        )

        chris.edited.add(html5)
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Dive into HTML5').values_list('name', flat=True)),
            ['Chris Mills']
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(edited__title='Dive into Python').values_list('name', flat=True)
            ),
            ['Chris Mills']
        )

        # Remove the second editor
        chris.edited.remove(html5)
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Dive into HTML5').values_list('name', flat=True)),
            []
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(edited__title='Dive into Python').values_list('name', flat=True)
            ),
            ['Chris Mills']
        )

        # Clear all edited books
        chris.edited.clear()
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Dive into HTML5').values_list('name', flat=True)),
            []
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(edited__title='Dive into Python').values_list('name', flat=True)
            ),
            []
        )

        # Create an author through the m2m interface
        chris.edited.create(title='Dive into Water', published=datetime.date(2010, 3, 15))
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Dive into HTML5').values_list('name', flat=True)),
            []
        )
        self.assertEqual(
            list(Person.objects.using('other').filter(edited__title='Dive into Water').values_list('name', flat=True)),
            ['Chris Mills']
        )
        self.assertEqual(
            list(
                Person.objects.using('other').filter(edited__title='Dive into Python').values_list('name', flat=True)
            ),
            []
        )

    def test_foreign_key_cross_database_protection(self):
        "Operations that involve sharing FK objects across databases raise an error"
        # Create a book and author on the default database
        pro = Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))
        marty = Person.objects.create(name="Marty Alchin")

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        # Set a foreign key with an object from a different database
        msg = (
            'Cannot assign "<Person: Marty Alchin>": the current database '
            'router prevents this relation.'
        )
        with self.assertRaisesMessage(ValueError, msg):
            dive.editor = marty

        # Set a foreign key set with an object from a different database
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='default'):
                marty.edited.set([pro, dive])

        # Add to a foreign key set with an object from a different database
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='default'):
                marty.edited.add(dive)

    def test_foreign_key_deletion(self):
        "Cascaded deletions of Foreign Key relations issue queries on the right database"
        mark = Person.objects.using('other').create(name="Mark Pilgrim")
        Pet.objects.using('other').create(name="Fido", owner=mark)

        # Check the initial state
        self.assertEqual(Person.objects.using('default').count(), 0)
        self.assertEqual(Pet.objects.using('default').count(), 0)

        self.assertEqual(Person.objects.using('other').count(), 1)
        self.assertEqual(Pet.objects.using('other').count(), 1)

        # Delete the person object, which will cascade onto the pet
        mark.delete(using='other')

        self.assertEqual(Person.objects.using('default').count(), 0)
        self.assertEqual(Pet.objects.using('default').count(), 0)

        # Both the pet and the person have been deleted from the right database
        self.assertEqual(Person.objects.using('other').count(), 0)
        self.assertEqual(Pet.objects.using('other').count(), 0)

    def test_foreign_key_validation(self):
        "ForeignKey.validate() uses the correct database"
        mickey = Person.objects.using('other').create(name="Mickey")
        pluto = Pet.objects.using('other').create(name="Pluto", owner=mickey)
        self.assertIsNone(pluto.full_clean())

    # Any router that accesses `model` in db_for_read() works here.
    @override_settings(DATABASE_ROUTERS=[AuthRouter()])
    def test_foreign_key_validation_with_router(self):
        """
        ForeignKey.validate() passes `model` to db_for_read() even if
        model_instance=None.
        """
        mickey = Person.objects.create(name="Mickey")
        owner_field = Pet._meta.get_field('owner')
        self.assertEqual(owner_field.clean(mickey.pk, None), mickey.pk)

    def test_o2o_separation(self):
        "OneToOne fields are constrained to a single database"
        # Create a user and profile on the default database
        alice = User.objects.db_manager('default').create_user('alice', 'alice@example.com')
        alice_profile = UserProfile.objects.using('default').create(user=alice, flavor='chocolate')

        # Create a user and profile on the other database
        bob = User.objects.db_manager('other').create_user('bob', 'bob@example.com')
        bob_profile = UserProfile.objects.using('other').create(user=bob, flavor='crunchy frog')

        # Retrieve related objects; queries should be database constrained
        alice = User.objects.using('default').get(username="alice")
        self.assertEqual(alice.userprofile.flavor, "chocolate")

        bob = User.objects.using('other').get(username="bob")
        self.assertEqual(bob.userprofile.flavor, "crunchy frog")

        # Queries work across joins
        self.assertEqual(
            list(
                User.objects.using('default')
                .filter(userprofile__flavor='chocolate').values_list('username', flat=True)
            ),
            ['alice']
        )
        self.assertEqual(
            list(
                User.objects.using('other')
                .filter(userprofile__flavor='chocolate').values_list('username', flat=True)
            ),
            []
        )

        self.assertEqual(
            list(
                User.objects.using('default')
                .filter(userprofile__flavor='crunchy frog').values_list('username', flat=True)
            ),
            []
        )
        self.assertEqual(
            list(
                User.objects.using('other')
                .filter(userprofile__flavor='crunchy frog').values_list('username', flat=True)
            ),
            ['bob']
        )

        # Reget the objects to clear caches
        alice_profile = UserProfile.objects.using('default').get(flavor='chocolate')
        bob_profile = UserProfile.objects.using('other').get(flavor='crunchy frog')

        # Retrieve related object by descriptor. Related objects should be database-bound
        self.assertEqual(alice_profile.user.username, 'alice')
        self.assertEqual(bob_profile.user.username, 'bob')

    def test_o2o_cross_database_protection(self):
        "Operations that involve sharing FK objects across databases raise an error"
        # Create a user and profile on the default database
        alice = User.objects.db_manager('default').create_user('alice', 'alice@example.com')

        # Create a user and profile on the other database
        bob = User.objects.db_manager('other').create_user('bob', 'bob@example.com')

        # Set a one-to-one relation with an object from a different database
        alice_profile = UserProfile.objects.using('default').create(user=alice, flavor='chocolate')
        msg = (
            'Cannot assign "%r": the current database router prevents this '
            'relation.' % alice_profile
        )
        with self.assertRaisesMessage(ValueError, msg):
            bob.userprofile = alice_profile

        # BUT! if you assign a FK object when the base object hasn't
        # been saved yet, you implicitly assign the database for the
        # base object.
        bob_profile = UserProfile.objects.using('other').create(user=bob, flavor='crunchy frog')

        new_bob_profile = UserProfile(flavor="spring surprise")

        # assigning a profile requires an explicit pk as the object isn't saved
        charlie = User(pk=51, username='charlie', email='charlie@example.com')
        charlie.set_unusable_password()

        # initially, no db assigned
        self.assertIsNone(new_bob_profile._state.db)
        self.assertIsNone(charlie._state.db)

        # old object comes from 'other', so the new object is set to use 'other'...
        new_bob_profile.user = bob
        charlie.userprofile = bob_profile
        self.assertEqual(new_bob_profile._state.db, 'other')
        self.assertEqual(charlie._state.db, 'other')

        # ... but it isn't saved yet
        self.assertEqual(list(User.objects.using('other').values_list('username', flat=True)), ['bob'])
        self.assertEqual(list(UserProfile.objects.using('other').values_list('flavor', flat=True)), ['crunchy frog'])

        # When saved (no using required), new objects goes to 'other'
        charlie.save()
        bob_profile.save()
        new_bob_profile.save()
        self.assertEqual(list(User.objects.using('default').values_list('username', flat=True)), ['alice'])
        self.assertEqual(list(User.objects.using('other').values_list('username', flat=True)), ['bob', 'charlie'])
        self.assertEqual(list(UserProfile.objects.using('default').values_list('flavor', flat=True)), ['chocolate'])
        self.assertEqual(
            list(UserProfile.objects.using('other').values_list('flavor', flat=True)),
            ['crunchy frog', 'spring surprise']
        )

        # This also works if you assign the O2O relation in the constructor
        denise = User.objects.db_manager('other').create_user('denise', 'denise@example.com')
        denise_profile = UserProfile(flavor="tofu", user=denise)

        self.assertEqual(denise_profile._state.db, 'other')
        # ... but it isn't saved yet
        self.assertEqual(list(UserProfile.objects.using('default').values_list('flavor', flat=True)), ['chocolate'])
        self.assertEqual(
            list(UserProfile.objects.using('other').values_list('flavor', flat=True)),
            ['crunchy frog', 'spring surprise']
        )

        # When saved, the new profile goes to 'other'
        denise_profile.save()
        self.assertEqual(list(UserProfile.objects.using('default').values_list('flavor', flat=True)), ['chocolate'])
        self.assertEqual(
            list(UserProfile.objects.using('other').values_list('flavor', flat=True)),
            ['crunchy frog', 'spring surprise', 'tofu']
        )

    def test_generic_key_separation(self):
        "Generic fields are constrained to a single database"
        # Create a book and author on the default database
        pro = Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))
        review1 = Review.objects.create(source="Python Monthly", content_object=pro)

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        review2 = Review.objects.using('other').create(source="Python Weekly", content_object=dive)

        review1 = Review.objects.using('default').get(source="Python Monthly")
        self.assertEqual(review1.content_object.title, "Pro Django")

        review2 = Review.objects.using('other').get(source="Python Weekly")
        self.assertEqual(review2.content_object.title, "Dive into Python")

        # Reget the objects to clear caches
        dive = Book.objects.using('other').get(title="Dive into Python")

        # Retrieve related object by descriptor. Related objects should be database-bound
        self.assertEqual(list(dive.reviews.all().values_list('source', flat=True)), ['Python Weekly'])

    def test_generic_key_reverse_operations(self):
        "Generic reverse manipulations are all constrained to a single DB"
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        temp = Book.objects.using('other').create(title="Temp", published=datetime.date(2009, 5, 4))
        review1 = Review.objects.using('other').create(source="Python Weekly", content_object=dive)
        review2 = Review.objects.using('other').create(source="Python Monthly", content_object=temp)

        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=dive.pk).values_list('source', flat=True)),
            []
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            ['Python Weekly']
        )

        # Add a second review
        dive.reviews.add(review2)
        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=dive.pk).values_list('source', flat=True)),
            []
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            ['Python Monthly', 'Python Weekly']
        )

        # Remove the second author
        dive.reviews.remove(review1)
        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=dive.pk).values_list('source', flat=True)),
            []
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            ['Python Monthly']
        )

        # Clear all reviews
        dive.reviews.clear()
        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=dive.pk).values_list('source', flat=True)),
            []
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            []
        )

        # Create an author through the generic interface
        dive.reviews.create(source='Python Daily')
        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=dive.pk).values_list('source', flat=True)),
            []
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            ['Python Daily']
        )

    def test_generic_key_cross_database_protection(self):
        "Operations that involve sharing generic key objects across databases raise an error"
        # Create a book and author on the default database
        pro = Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))
        review1 = Review.objects.create(source="Python Monthly", content_object=pro)

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        Review.objects.using('other').create(source="Python Weekly", content_object=dive)

        # Set a foreign key with an object from a different database
        msg = (
            'Cannot assign "<ContentType: multiple_database | book>": the '
            'current database router prevents this relation.'
        )
        with self.assertRaisesMessage(ValueError, msg):
            review1.content_object = dive

        # Add to a foreign key set with an object from a different database
        msg = (
            "<Review: Python Monthly> instance isn't saved. "
            "Use bulk=False or save the object first."
        )
        with self.assertRaisesMessage(ValueError, msg):
            with transaction.atomic(using='other'):
                dive.reviews.add(review1)

        # BUT! if you assign a FK object when the base object hasn't
        # been saved yet, you implicitly assign the database for the
        # base object.
        review3 = Review(source="Python Daily")
        # initially, no db assigned
        self.assertIsNone(review3._state.db)

        # Dive comes from 'other', so review3 is set to use 'other'...
        review3.content_object = dive
        self.assertEqual(review3._state.db, 'other')
        # ... but it isn't saved yet
        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=pro.pk).values_list('source', flat=True)),
            ['Python Monthly']
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            ['Python Weekly']
        )

        # When saved, John goes to 'other'
        review3.save()
        self.assertEqual(
            list(Review.objects.using('default').filter(object_id=pro.pk).values_list('source', flat=True)),
            ['Python Monthly']
        )
        self.assertEqual(
            list(Review.objects.using('other').filter(object_id=dive.pk).values_list('source', flat=True)),
            ['Python Daily', 'Python Weekly']
        )

    def test_generic_key_deletion(self):
        "Cascaded deletions of Generic Key relations issue queries on the right database"
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        Review.objects.using('other').create(source="Python Weekly", content_object=dive)

        # Check the initial state
        self.assertEqual(Book.objects.using('default').count(), 0)
        self.assertEqual(Review.objects.using('default').count(), 0)

        self.assertEqual(Book.objects.using('other').count(), 1)
        self.assertEqual(Review.objects.using('other').count(), 1)

        # Delete the Book object, which will cascade onto the pet
        dive.delete(using='other')

        self.assertEqual(Book.objects.using('default').count(), 0)
        self.assertEqual(Review.objects.using('default').count(), 0)

        # Both the pet and the person have been deleted from the right database
        self.assertEqual(Book.objects.using('other').count(), 0)
        self.assertEqual(Review.objects.using('other').count(), 0)

    def test_ordering(self):
        "get_next_by_XXX commands stick to a single database"
        Book.objects.create(title="Pro Django", published=datetime.date(2008, 12, 16))
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        learn = Book.objects.using('other').create(title="Learning Python", published=datetime.date(2008, 7, 16))

        self.assertEqual(learn.get_next_by_published().title, "Dive into Python")
        self.assertEqual(dive.get_previous_by_published().title, "Learning Python")

    def test_raw(self):
        "test the raw() method across databases"
        dive = Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))
        val = Book.objects.db_manager("other").raw('SELECT id FROM multiple_database_book')
        self.assertQuerysetEqual(val, [dive.pk], attrgetter("pk"))

        val = Book.objects.raw('SELECT id FROM multiple_database_book').using('other')
        self.assertQuerysetEqual(val, [dive.pk], attrgetter("pk"))

    def test_select_related(self):
        "Database assignment is retained if an object is retrieved with select_related()"
        # Create a book and author on the other database
        mark = Person.objects.using('other').create(name="Mark Pilgrim")
        Book.objects.using('other').create(
            title="Dive into Python",
            published=datetime.date(2009, 5, 4),
            editor=mark,
        )

        # Retrieve the Person using select_related()
        book = Book.objects.using('other').select_related('editor').get(title="Dive into Python")

        # The editor instance should have a db state
        self.assertEqual(book.editor._state.db, 'other')

    def test_subquery(self):
        """Make sure as_sql works with subqueries and primary/replica."""
        sub = Person.objects.using('other').filter(name='fff')
        qs = Book.objects.filter(editor__in=sub)

        # When you call __str__ on the query object, it doesn't know about using
        # so it falls back to the default. If the subquery explicitly uses a
        # different database, an error should be raised.
        msg = (
            "Subqueries aren't allowed across different databases. Force the "
            "inner query to be evaluated using `list(inner_query)`."
        )
        with self.assertRaisesMessage(ValueError, msg):
            str(qs.query)

        # Evaluating the query shouldn't work, either
        with self.assertRaisesMessage(ValueError, msg):
            for obj in qs:
                pass

    def test_related_manager(self):
        "Related managers return managers, not querysets"
        mark = Person.objects.using('other').create(name="Mark Pilgrim")

        # extra_arg is removed by the BookManager's implementation of
        # create(); but the BookManager's implementation won't get called
        # unless edited returns a Manager, not a queryset
        mark.book_set.create(title="Dive into Python", published=datetime.date(2009, 5, 4), extra_arg=True)
        mark.book_set.get_or_create(title="Dive into Python", published=datetime.date(2009, 5, 4), extra_arg=True)
        mark.edited.create(title="Dive into Water", published=datetime.date(2009, 5, 4), extra_arg=True)
        mark.edited.get_or_create(title="Dive into Water", published=datetime.date(2009, 5, 4), extra_arg=True)


class ConnectionRouterTestCase(SimpleTestCase):
    @override_settings(DATABASE_ROUTERS=[
        'multiple_database.tests.TestRouter',
        'multiple_database.tests.WriteRouter'])
    def test_router_init_default(self):
        connection_router = ConnectionRouter()
        self.assertEqual([r.__class__.__name__ for r in connection_router.routers], ['TestRouter', 'WriteRouter'])

    def test_router_init_arg(self):
        connection_router = ConnectionRouter([
            'multiple_database.tests.TestRouter',
            'multiple_database.tests.WriteRouter'
        ])
        self.assertEqual([r.__class__.__name__ for r in connection_router.routers], ['TestRouter', 'WriteRouter'])

        # Init with instances instead of strings
        connection_router = ConnectionRouter([TestRouter(), WriteRouter()])
        self.assertEqual([r.__class__.__name__ for r in connection_router.routers], ['TestRouter', 'WriteRouter'])


# Make the 'other' database appear to be a replica of the 'default'
@override_settings(DATABASE_ROUTERS=[TestRouter()])
class RouterTestCase(TestCase):
    databases = {'default', 'other'}

    def test_db_selection(self):
        "Querysets obey the router for db suggestions"
        self.assertEqual(Book.objects.db, 'other')
        self.assertEqual(Book.objects.all().db, 'other')

        self.assertEqual(Book.objects.using('default').db, 'default')

        self.assertEqual(Book.objects.db_manager('default').db, 'default')
        self.assertEqual(Book.objects.db_manager('default').all().db, 'default')

    def test_migrate_selection(self):
        "Synchronization behavior is predictable"

        self.assertTrue(router.allow_migrate_model('default', User))
        self.assertTrue(router.allow_migrate_model('default', Book))

        self.assertTrue(router.allow_migrate_model('other', User))
        self.assertTrue(router.allow_migrate_model('other', Book))

        with override_settings(DATABASE_ROUTERS=[TestRouter(), AuthRouter()]):
            # Add the auth router to the chain. TestRouter is a universal
            # synchronizer, so it should have no effect.
            self.assertTrue(router.allow_migrate_model('default', User))
            self.assertTrue(router.allow_migrate_model('default', Book))

            self.assertTrue(router.allow_migrate_model('other', User))
            self.assertTrue(router.allow_migrate_model('other', Book))

        with override_settings(DATABASE_ROUTERS=[AuthRouter(), TestRouter()]):
            # Now check what happens if the router order is reversed.
            self.assertFalse(router.allow_migrate_model('default', User))
            self.assertTrue(router.allow_migrate_model('default', Book))

            self.assertTrue(router.allow_migrate_model('other', User))
            self.assertTrue(router.allow_migrate_model('other', Book))

    def test_partial_router(self):
        "A router can choose to implement a subset of methods"
        dive = Book.objects.using('other').create(title="Dive into Python",
                                                  published=datetime.date(2009, 5, 4))

        # First check the baseline behavior.

        self.assertEqual(router.db_for_read(User), 'other')
        self.assertEqual(router.db_for_read(Book), 'other')

        self.assertEqual(router.db_for_write(User), 'default')
        self.assertEqual(router.db_for_write(Book), 'default')

        self.assertTrue(router.allow_relation(dive, dive))

        self.assertTrue(router.allow_migrate_model('default', User))
        self.assertTrue(router.allow_migrate_model('default', Book))

        with override_settings(DATABASE_ROUTERS=[WriteRouter(), AuthRouter(), TestRouter()]):
            self.assertEqual(router.db_for_read(User), 'default')
            self.assertEqual(router.db_for_read(Book), 'other')

            self.assertEqual(router.db_for_write(User), 'writer')
            self.assertEqual(router.db_for_write(Book), 'writer')

            self.assertTrue(router.allow_relation(dive, dive))

            self.assertFalse(router.allow_migrate_model('default', User))
            self.assertTrue(router.allow_migrate_model('default', Book))

    def test_database_routing(self):
        marty = Person.objects.using('default').create(name="Marty Alchin")
        pro = Book.objects.using('default').create(
            title='Pro Django',
            published=datetime.date(2008, 12, 16),
            editor=marty,
        )
        pro.authors.set([marty])

        # Create a book and author on the other database
        Book.objects.using('other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        # An update query will be routed to the default database
        Book.objects.filter(title='Pro Django').update(pages=200)

        with self.assertRaises(Book.DoesNotExist):
            # By default, the get query will be directed to 'other'
            Book.objects.get(title='Pro Django')

        # But the same query issued explicitly at a database will work.
        pro = Book.objects.using('default').get(title='Pro Django')

        # The update worked.
        self.assertEqual(pro.pages, 200)

        # An update query with an explicit using clause will be routed
        # to the requested database.
        Book.objects.using('other').filter(title='Dive into Python').update(pages=300)
        self.assertEqual(Book.objects.get(title='Dive into Python').pages, 300)

        # Related object queries stick to the same database
        # as the original object, regardless of the router
        self.assertEqual(list(pro.authors.values_list('name', flat=True)), ['Marty Alchin'])
        self.assertEqual(pro.editor.name, 'Marty Alchin')

        # get_or_create is a special case. The get needs to be targeted at
        # the write database in order to avoid potential transaction
        # consistency problems
        book, created = Book.objects.get_or_create(title="Pro Django")
        self.assertFalse(created)

        book, created = Book.objects.get_or_create(title="Dive Into Python",
                                                   defaults={'published': datetime.date(2009, 5, 4)})
        self.assertTrue(created)

        # Check the head count of objects
        self.assertEqual(Book.objects.using('default').count(), 2)
        self.assertEqual(Book.objects.using('other').count(), 1)
        # If a database isn't specified, the read database is used
        self.assertEqual(Book.objects.count(), 1)

        # A delete query will also be routed to the default database
        Book.objects.filter(pages__gt=150).delete()

        # The default database has lost the book.
        self.assertEqual(Book.objects.using('default').count(), 1)
        self.assertEqual(Book.objects.using('other').count(), 1)

    def test_invalid_set_foreign_key_assignment(self):
        marty = Person.objects.using('default').create(name="Marty Alchin")
        dive = Book.objects.using('other').create(
            title="Dive into Python",
            published=datetime.date(2009, 5, 4),
        )
        # Set a foreign key set with an object from a different database
        msg = "<Book: Dive into Python> instance isn't saved. Use bulk=False or save the object first."
        with self.assertRaisesMessage(ValueError, msg):
            marty.edited.set([dive])

    def test_foreign_key_cross_database_protection(self):
        "Foreign keys can cross databases if they two databases have a common source"
        # Create a book and author on the default database
        pro = Book.objects.using('default').create(title="Pro Django",
                                                   published=datetime.date(2008, 12, 16))

        marty = Person.objects.using('default').create(name="Marty Alchin")

        # Create a book and author on the other database
        dive = Book.objects.using('other').create(title="Dive into Python",
                                                  published=datetime.date(2009, 5, 4))

        mark = Person.objects.using('other').create(name="Mark Pilgrim")

        # Set a foreign key with an object from a different database
        dive.editor = marty

        # Database assignments of original objects haven't changed...
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(mark._state.db, 'other')

        # ... but they will when the affected object is saved.
        dive.save()
        self.assertEqual(dive._state.db, 'default')

        # ...and the source database now has a copy of any object saved
        Book.objects.using('default').get(title='Dive into Python').delete()

        # This isn't a real primary/replica database, so restore the original from other
        dive = Book.objects.using('other').get(title='Dive into Python')
        self.assertEqual(dive._state.db, 'other')

        # Set a foreign key set with an object from a different database
        marty.edited.set([pro, dive], bulk=False)

        # Assignment implies a save, so database assignments of original objects have changed...
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'default')
        self.assertEqual(mark._state.db, 'other')

        # ...and the source database now has a copy of any object saved
        Book.objects.using('default').get(title='Dive into Python').delete()

        # This isn't a real primary/replica database, so restore the original from other
        dive = Book.objects.using('other').get(title='Dive into Python')
        self.assertEqual(dive._state.db, 'other')

        # Add to a foreign key set with an object from a different database
        marty.edited.add(dive, bulk=False)

        # Add implies a save, so database assignments of original objects have changed...
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'default')
        self.assertEqual(mark._state.db, 'other')

        # ...and the source database now has a copy of any object saved
        Book.objects.using('default').get(title='Dive into Python').delete()

        # This isn't a real primary/replica database, so restore the original from other
        dive = Book.objects.using('other').get(title='Dive into Python')

        # If you assign a FK object when the base object hasn't
        # been saved yet, you implicitly assign the database for the
        # base object.
        chris = Person(name="Chris Mills")
        html5 = Book(title="Dive into HTML5", published=datetime.date(2010, 3, 15))
        # initially, no db assigned
        self.assertIsNone(chris._state.db)
        self.assertIsNone(html5._state.db)

        # old object comes from 'other', so the new object is set to use the
        # source of 'other'...
        self.assertEqual(dive._state.db, 'other')
        chris.save()
        dive.editor = chris
        html5.editor = mark

        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(mark._state.db, 'other')
        self.assertEqual(chris._state.db, 'default')
        self.assertEqual(html5._state.db, 'default')

        # This also works if you assign the FK in the constructor
        water = Book(title="Dive into Water", published=datetime.date(2001, 1, 1), editor=mark)
        self.assertEqual(water._state.db, 'default')

        # For the remainder of this test, create a copy of 'mark' in the
        # 'default' database to prevent integrity errors on backends that
        # don't defer constraints checks until the end of the transaction
        mark.save(using='default')

        # This moved 'mark' in the 'default' database, move it back in 'other'
        mark.save(using='other')
        self.assertEqual(mark._state.db, 'other')

        # If you create an object through a FK relation, it will be
        # written to the write database, even if the original object
        # was on the read database
        cheesecake = mark.edited.create(title='Dive into Cheesecake', published=datetime.date(2010, 3, 15))
        self.assertEqual(cheesecake._state.db, 'default')

        # Same goes for get_or_create, regardless of whether getting or creating
        cheesecake, created = mark.edited.get_or_create(
            title='Dive into Cheesecake',
            published=datetime.date(2010, 3, 15),
        )
        self.assertEqual(cheesecake._state.db, 'default')

        puddles, created = mark.edited.get_or_create(title='Dive into Puddles', published=datetime.date(2010, 3, 15))
        self.assertEqual(puddles._state.db, 'default')

    def test_m2m_cross_database_protection(self):
        "M2M relations can cross databases if the database share a source"
        # Create books and authors on the inverse to the usual database
        pro = Book.objects.using('other').create(pk=1, title="Pro Django",
                                                 published=datetime.date(2008, 12, 16))

        marty = Person.objects.using('other').create(pk=1, name="Marty Alchin")

        dive = Book.objects.using('default').create(pk=2, title="Dive into Python",
                                                    published=datetime.date(2009, 5, 4))

        mark = Person.objects.using('default').create(pk=2, name="Mark Pilgrim")

        # Now save back onto the usual database.
        # This simulates primary/replica - the objects exist on both database,
        # but the _state.db is as it is for all other tests.
        pro.save(using='default')
        marty.save(using='default')
        dive.save(using='other')
        mark.save(using='other')

        # We have 2 of both types of object on both databases
        self.assertEqual(Book.objects.using('default').count(), 2)
        self.assertEqual(Book.objects.using('other').count(), 2)
        self.assertEqual(Person.objects.using('default').count(), 2)
        self.assertEqual(Person.objects.using('other').count(), 2)

        # Set a m2m set with an object from a different database
        marty.book_set.set([pro, dive])

        # Database assignments don't change
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(mark._state.db, 'other')

        # All m2m relations should be saved on the default database
        self.assertEqual(Book.authors.through.objects.using('default').count(), 2)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

        # Reset relations
        Book.authors.through.objects.using('default').delete()

        # Add to an m2m with an object from a different database
        marty.book_set.add(dive)

        # Database assignments don't change
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(mark._state.db, 'other')

        # All m2m relations should be saved on the default database
        self.assertEqual(Book.authors.through.objects.using('default').count(), 1)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

        # Reset relations
        Book.authors.through.objects.using('default').delete()

        # Set a reverse m2m with an object from a different database
        dive.authors.set([mark, marty])

        # Database assignments don't change
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(mark._state.db, 'other')

        # All m2m relations should be saved on the default database
        self.assertEqual(Book.authors.through.objects.using('default').count(), 2)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

        # Reset relations
        Book.authors.through.objects.using('default').delete()

        self.assertEqual(Book.authors.through.objects.using('default').count(), 0)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

        # Add to a reverse m2m with an object from a different database
        dive.authors.add(marty)

        # Database assignments don't change
        self.assertEqual(marty._state.db, 'default')
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(mark._state.db, 'other')

        # All m2m relations should be saved on the default database
        self.assertEqual(Book.authors.through.objects.using('default').count(), 1)
        self.assertEqual(Book.authors.through.objects.using('other').count(), 0)

        # If you create an object through a M2M relation, it will be
        # written to the write database, even if the original object
        # was on the read database
        alice = dive.authors.create(name='Alice')
        self.assertEqual(alice._state.db, 'default')

        # Same goes for get_or_create, regardless of whether getting or creating
        alice, created = dive.authors.get_or_create(name='Alice')
        self.assertEqual(alice._state.db, 'default')

        bob, created = dive.authors.get_or_create(name='Bob')
        self.assertEqual(bob._state.db, 'default')

    def test_o2o_cross_database_protection(self):
        "Operations that involve sharing FK objects across databases raise an error"
        # Create a user and profile on the default database
        alice = User.objects.db_manager('default').create_user('alice', 'alice@example.com')

        # Create a user and profile on the other database
        bob = User.objects.db_manager('other').create_user('bob', 'bob@example.com')

        # Set a one-to-one relation with an object from a different database
        alice_profile = UserProfile.objects.create(user=alice, flavor='chocolate')
        bob.userprofile = alice_profile

        # Database assignments of original objects haven't changed...
        self.assertEqual(alice._state.db, 'default')
        self.assertEqual(alice_profile._state.db, 'default')
        self.assertEqual(bob._state.db, 'other')

        # ... but they will when the affected object is saved.
        bob.save()
        self.assertEqual(bob._state.db, 'default')

    def test_generic_key_cross_database_protection(self):
        "Generic Key operations can span databases if they share a source"
        # Create a book and author on the default database
        pro = Book.objects.using(
            'default').create(title="Pro Django", published=datetime.date(2008, 12, 16))

        review1 = Review.objects.using(
            'default').create(source="Python Monthly", content_object=pro)

        # Create a book and author on the other database
        dive = Book.objects.using(
            'other').create(title="Dive into Python", published=datetime.date(2009, 5, 4))

        review2 = Review.objects.using(
            'other').create(source="Python Weekly", content_object=dive)

        # Set a generic foreign key with an object from a different database
        review1.content_object = dive

        # Database assignments of original objects haven't changed...
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(review1._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(review2._state.db, 'other')

        # ... but they will when the affected object is saved.
        dive.save()
        self.assertEqual(review1._state.db, 'default')
        self.assertEqual(dive._state.db, 'default')

        # ...and the source database now has a copy of any object saved
        Book.objects.using('default').get(title='Dive into Python').delete()

        # This isn't a real primary/replica database, so restore the original from other
        dive = Book.objects.using('other').get(title='Dive into Python')
        self.assertEqual(dive._state.db, 'other')

        # Add to a generic foreign key set with an object from a different database
        dive.reviews.add(review1)

        # Database assignments of original objects haven't changed...
        self.assertEqual(pro._state.db, 'default')
        self.assertEqual(review1._state.db, 'default')
        self.assertEqual(dive._state.db, 'other')
        self.assertEqual(review2._state.db, 'other')

        # ... but they will when the affected object is saved.
        dive.save()
        self.assertEqual(dive._state.db, 'default')

        # ...and the source database now has a copy of any object saved
        Book.objects.using('default').get(title='Dive into Python').delete()

        # BUT! if you assign a FK object when the base object hasn't
        # been saved yet, you implicitly assign the database for the
        # base object.
        review3 = Review(source="Python Daily")
        # initially, no db assigned
        self.assertIsNone(review3._state.db)

        # Dive comes from 'other', so review3 is set to use the source of 'other'...
        review3.content_object = dive
        self.assertEqual(review3._state.db, 'default')

        # If you create an object through a M2M relation, it will be
        # written to the write database, even if the original object
        # was on the read database
        dive = Book.objects.using('other').get(title='Dive into Python')
        nyt = dive.reviews.create(source="New York Times", content_object=dive)
        self.assertEqual(nyt._state.db, 'default')

    def test_m2m_managers(self):
        "M2M relations are represented by managers, and can be controlled like managers"
        pro = Book.objects.using('other').create(pk=1, title="Pro Django",
                                                 published=datetime.date(2008, 12, 16))

        marty = Person.objects.using('other').create(pk=1, name="Marty Alchin")

        self.assertEqual(pro.authors.db, 'other')
        self.assertEqual(pro.authors.db_manager('default').db, 'default')
        self.assertEqual(pro.authors.db_manager('default').all().db, 'default')

        self.assertEqual(marty.book_set.db, 'other')
        self.assertEqual(marty.book_set.db_manager('default').db, 'default')
        self.assertEqual(marty.book_set.db_manager('default').all().db, 'default')

    def test_foreign_key_managers(self):
        "FK reverse relations are represented by managers, and can be controlled like managers"
        marty = Person.objects.using('other').create(pk=1, name="Marty Alchin")
        Book.objects.using('other').create(
            pk=1,
            title='Pro Django',
            published=datetime.date(2008, 12, 16),
            editor=marty,
        )
        self.assertEqual(marty.edited.db, 'other')
        self.assertEqual(marty.edited.db_manager('default').db, 'default')
        self.assertEqual(marty.edited.db_manager('default').all().db, 'default')

    def test_generic_key_managers(self):
        "Generic key relations are represented by managers, and can be controlled like managers"
        pro = Book.objects.using('other').create(title="Pro Django",
                                                 published=datetime.date(2008, 12, 16))

        Review.objects.using('other').create(source='Python Monthly', content_object=pro)

        self.assertEqual(pro.reviews.db, 'other')
        self.assertEqual(pro.reviews.db_manager('default').db, 'default')
        self.assertEqual(pro.reviews.db_manager('default').all().db, 'default')

    def test_subquery(self):
        """Make sure as_sql works with subqueries and primary/replica."""
        # Create a book and author on the other database

        mark = Person.objects.using('other').create(name="Mark Pilgrim")
        Book.objects.using('other').create(
            title='Dive into Python',
            published=datetime.date(2009, 5, 4),
            editor=mark,
        )

        sub = Person.objects.filter(name='Mark Pilgrim')
        qs = Book.objects.filter(editor__in=sub)

        # When you call __str__ on the query object, it doesn't know about using
        # so it falls back to the default. Don't let routing instructions
        # force the subquery to an incompatible database.
        str(qs.query)

        # If you evaluate the query, it should work, running on 'other'
        self.assertEqual(list(qs.values_list('title', flat=True)), ['Dive into Python'])

    def test_deferred_models(self):
        mark_def = Person.objects.using('default').create(name="Mark Pilgrim")
        mark_other = Person.objects.using('other').create(name="Mark Pilgrim")
        orig_b = Book.objects.using('other').create(
            title='Dive into Python',
            published=datetime.date(2009, 5, 4),
            editor=mark_other,
        )
        b = Book.objects.using('other').only('title').get(pk=orig_b.pk)
        self.assertEqual(b.published, datetime.date(2009, 5, 4))
        b = Book.objects.using('other').only('title').get(pk=orig_b.pk)
        b.editor = mark_def
        b.save(using='default')
        self.assertEqual(Book.objects.using('default').get(pk=b.pk).published,
                         datetime.date(2009, 5, 4))


@override_settings(DATABASE_ROUTERS=[AuthRouter()])
class AuthTestCase(TestCase):
    databases = {'default', 'other'}

    def test_auth_manager(self):
        "The methods on the auth manager obey database hints"
        # Create one user using default allocation policy
        User.objects.create_user('alice', 'alice@example.com')

        # Create another user, explicitly specifying the database
        User.objects.db_manager('default').create_user('bob', 'bob@example.com')

        # The second user only exists on the other database
        alice = User.objects.using('other').get(username='alice')

        self.assertEqual(alice.username, 'alice')
        self.assertEqual(alice._state.db, 'other')

        with self.assertRaises(User.DoesNotExist):
            User.objects.using('default').get(username='alice')

        # The second user only exists on the default database
        bob = User.objects.using('default').get(username='bob')

        self.assertEqual(bob.username, 'bob')
        self.assertEqual(bob._state.db, 'default')

        with self.assertRaises(User.DoesNotExist):
            User.objects.using('other').get(username='bob')

        # That is... there is one user on each database
        self.assertEqual(User.objects.using('default').count(), 1)
        self.assertEqual(User.objects.using('other').count(), 1)

    def test_dumpdata(self):
        "dumpdata honors allow_migrate restrictions on the router"
        User.objects.create_user('alice', 'alice@example.com')
        User.objects.db_manager('default').create_user('bob', 'bob@example.com')

        # dumping the default database doesn't try to include auth because
        # allow_migrate prohibits auth on default
        new_io = StringIO()
        management.call_command('dumpdata', 'auth', format='json', database='default', stdout=new_io)
        command_output = new_io.getvalue().strip()
        self.assertEqual(command_output, '[]')

        # dumping the other database does include auth
        new_io = StringIO()
        management.call_command('dumpdata', 'auth', format='json', database='other', stdout=new_io)
        command_output = new_io.getvalue().strip()
        self.assertIn('"email": "alice@example.com"', command_output)


class AntiPetRouter:
    # A router that only expresses an opinion on migrate,
    # passing pets to the 'other' database

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        if db == 'other':
            return model_name == 'pet'
        else:
            return model_name != 'pet'


class FixtureTestCase(TestCase):
    databases = {'default', 'other'}
    fixtures = ['multidb-common', 'multidb']

    @override_settings(DATABASE_ROUTERS=[AntiPetRouter()])
    def test_fixture_loading(self):
        "Multi-db fixtures are loaded correctly"
        # "Pro Django" exists on the default database, but not on other database
        Book.objects.get(title="Pro Django")
        Book.objects.using('default').get(title="Pro Django")

        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('other').get(title="Pro Django")

        # "Dive into Python" exists on the default database, but not on other database
        Book.objects.using('other').get(title="Dive into Python")

        with self.assertRaises(Book.DoesNotExist):
            Book.objects.get(title="Dive into Python")
        with self.assertRaises(Book.DoesNotExist):
            Book.objects.using('default').get(title="Dive into Python")

        # "Definitive Guide" exists on the both databases
        Book.objects.get(title="The Definitive Guide to Django")
        Book.objects.using('default').get(title="The Definitive Guide to Django")
        Book.objects.using('other').get(title="The Definitive Guide to Django")

    @override_settings(DATABASE_ROUTERS=[AntiPetRouter()])
    def test_pseudo_empty_fixtures(self):
        """
        A fixture can contain entries, but lead to nothing in the database;
        this shouldn't raise an error (#14068).
        """
        new_io = StringIO()
        management.call_command('loaddata', 'pets', stdout=new_io, stderr=new_io)
        command_output = new_io.getvalue().strip()
        # No objects will actually be loaded
        self.assertEqual(command_output, "Installed 0 object(s) (of 2) from 1 fixture(s)")


class PickleQuerySetTestCase(TestCase):
    databases = {'default', 'other'}

    def test_pickling(self):
        for db in connections:
            Book.objects.using(db).create(title='Dive into Python', published=datetime.date(2009, 5, 4))
            qs = Book.objects.all()
            self.assertEqual(qs.db, pickle.loads(pickle.dumps(qs)).db)


class DatabaseReceiver:
    """
    Used in the tests for the database argument in signals (#13552)
    """
    def __call__(self, signal, sender, **kwargs):
        self._database = kwargs['using']


class WriteToOtherRouter:
    """
    A router that sends all writes to the other database.
    """
    def db_for_write(self, model, **hints):
        return "other"


class SignalTests(TestCase):
    databases = {'default', 'other'}

    def override_router(self):
        return override_settings(DATABASE_ROUTERS=[WriteToOtherRouter()])

    def test_database_arg_save_and_delete(self):
        """
        The pre/post_save signal contains the correct database.
        """
        # Make some signal receivers
        pre_save_receiver = DatabaseReceiver()
        post_save_receiver = DatabaseReceiver()
        pre_delete_receiver = DatabaseReceiver()
        post_delete_receiver = DatabaseReceiver()
        # Make model and connect receivers
        signals.pre_save.connect(sender=Person, receiver=pre_save_receiver)
        signals.post_save.connect(sender=Person, receiver=post_save_receiver)
        signals.pre_delete.connect(sender=Person, receiver=pre_delete_receiver)
        signals.post_delete.connect(sender=Person, receiver=post_delete_receiver)
        p = Person.objects.create(name='Darth Vader')
        # Save and test receivers got calls
        p.save()
        self.assertEqual(pre_save_receiver._database, DEFAULT_DB_ALIAS)
        self.assertEqual(post_save_receiver._database, DEFAULT_DB_ALIAS)
        # Delete, and test
        p.delete()
        self.assertEqual(pre_delete_receiver._database, DEFAULT_DB_ALIAS)
        self.assertEqual(post_delete_receiver._database, DEFAULT_DB_ALIAS)
        # Save again to a different database
        p.save(using="other")
        self.assertEqual(pre_save_receiver._database, "other")
        self.assertEqual(post_save_receiver._database, "other")
        # Delete, and test
        p.delete(using="other")
        self.assertEqual(pre_delete_receiver._database, "other")
        self.assertEqual(post_delete_receiver._database, "other")

        signals.pre_save.disconnect(sender=Person, receiver=pre_save_receiver)
        signals.post_save.disconnect(sender=Person, receiver=post_save_receiver)
        signals.pre_delete.disconnect(sender=Person, receiver=pre_delete_receiver)
        signals.post_delete.disconnect(sender=Person, receiver=post_delete_receiver)

    def test_database_arg_m2m(self):
        """
        The m2m_changed signal has a correct database arg.
        """
        # Make a receiver
        receiver = DatabaseReceiver()
        # Connect it
        signals.m2m_changed.connect(receiver=receiver)

        # Create the models that will be used for the tests
        b = Book.objects.create(title="Pro Django",
                                published=datetime.date(2008, 12, 16))
        p = Person.objects.create(name="Marty Alchin")

        # Create a copy of the models on the 'other' database to prevent
        # integrity errors on backends that don't defer constraints checks
        Book.objects.using('other').create(pk=b.pk, title=b.title, published=b.published)
        Person.objects.using('other').create(pk=p.pk, name=p.name)

        # Test addition
        b.authors.add(p)
        self.assertEqual(receiver._database, DEFAULT_DB_ALIAS)
        with self.override_router():
            b.authors.add(p)
        self.assertEqual(receiver._database, "other")

        # Test removal
        b.authors.remove(p)
        self.assertEqual(receiver._database, DEFAULT_DB_ALIAS)
        with self.override_router():
            b.authors.remove(p)
        self.assertEqual(receiver._database, "other")

        # Test addition in reverse
        p.book_set.add(b)
        self.assertEqual(receiver._database, DEFAULT_DB_ALIAS)
        with self.override_router():
            p.book_set.add(b)
        self.assertEqual(receiver._database, "other")

        # Test clearing
        b.authors.clear()
        self.assertEqual(receiver._database, DEFAULT_DB_ALIAS)
        with self.override_router():
            b.authors.clear()
        self.assertEqual(receiver._database, "other")


class AttributeErrorRouter:
    "A router to test the exception handling of ConnectionRouter"
    def db_for_read(self, model, **hints):
        raise AttributeError

    def db_for_write(self, model, **hints):
        raise AttributeError


class RouterAttributeErrorTestCase(TestCase):
    databases = {'default', 'other'}

    def override_router(self):
        return override_settings(DATABASE_ROUTERS=[AttributeErrorRouter()])

    def test_attribute_error_read(self):
        "The AttributeError from AttributeErrorRouter bubbles up"
        b = Book.objects.create(title="Pro Django",
                                published=datetime.date(2008, 12, 16))
        with self.override_router():
            with self.assertRaises(AttributeError):
                Book.objects.get(pk=b.pk)

    def test_attribute_error_save(self):
        "The AttributeError from AttributeErrorRouter bubbles up"
        dive = Book()
        dive.title = "Dive into Python"
        dive.published = datetime.date(2009, 5, 4)
        with self.override_router():
            with self.assertRaises(AttributeError):
                dive.save()

    def test_attribute_error_delete(self):
        "The AttributeError from AttributeErrorRouter bubbles up"
        b = Book.objects.create(title="Pro Django",
                                published=datetime.date(2008, 12, 16))
        p = Person.objects.create(name="Marty Alchin")
        b.authors.set([p])
        b.editor = p
        with self.override_router():
            with self.assertRaises(AttributeError):
                b.delete()

    def test_attribute_error_m2m(self):
        "The AttributeError from AttributeErrorRouter bubbles up"
        b = Book.objects.create(title="Pro Django",
                                published=datetime.date(2008, 12, 16))
        p = Person.objects.create(name="Marty Alchin")
        with self.override_router():
            with self.assertRaises(AttributeError):
                b.authors.set([p])


class ModelMetaRouter:
    "A router to ensure model arguments are real model classes"
    def db_for_write(self, model, **hints):
        if not hasattr(model, '_meta'):
            raise ValueError


@override_settings(DATABASE_ROUTERS=[ModelMetaRouter()])
class RouterModelArgumentTestCase(TestCase):
    databases = {'default', 'other'}

    def test_m2m_collection(self):
        b = Book.objects.create(title="Pro Django",
                                published=datetime.date(2008, 12, 16))

        p = Person.objects.create(name="Marty Alchin")
        # test add
        b.authors.add(p)
        # test remove
        b.authors.remove(p)
        # test clear
        b.authors.clear()
        # test setattr
        b.authors.set([p])
        # test M2M collection
        b.delete()

    def test_foreignkey_collection(self):
        person = Person.objects.create(name='Bob')
        Pet.objects.create(owner=person, name='Wart')
        # test related FK collection
        person.delete()


class SyncOnlyDefaultDatabaseRouter:
    def allow_migrate(self, db, app_label, **hints):
        return db == DEFAULT_DB_ALIAS


class MigrateTestCase(TestCase):

    # Limit memory usage when calling 'migrate'.
    available_apps = [
        'multiple_database',
        'django.contrib.auth',
        'django.contrib.contenttypes'
    ]
    databases = {'default', 'other'}

    def test_migrate_to_other_database(self):
        """Regression test for #16039: migrate with --database option."""
        cts = ContentType.objects.using('other').filter(app_label='multiple_database')

        count = cts.count()
        self.assertGreater(count, 0)

        cts.delete()
        management.call_command('migrate', verbosity=0, interactive=False, database='other')
        self.assertEqual(cts.count(), count)

    def test_migrate_to_other_database_with_router(self):
        """Regression test for #16039: migrate with --database option."""
        cts = ContentType.objects.using('other').filter(app_label='multiple_database')

        cts.delete()
        with override_settings(DATABASE_ROUTERS=[SyncOnlyDefaultDatabaseRouter()]):
            management.call_command('migrate', verbosity=0, interactive=False, database='other')

        self.assertEqual(cts.count(), 0)


class RouterUsed(Exception):
    WRITE = 'write'

    def __init__(self, mode, model, hints):
        self.mode = mode
        self.model = model
        self.hints = hints


class RouteForWriteTestCase(TestCase):
    databases = {'default', 'other'}

    class WriteCheckRouter:
        def db_for_write(self, model, **hints):
            raise RouterUsed(mode=RouterUsed.WRITE, model=model, hints=hints)

    def override_router(self):
        return override_settings(DATABASE_ROUTERS=[RouteForWriteTestCase.WriteCheckRouter()])

    def test_fk_delete(self):
        owner = Person.objects.create(name='Someone')
        pet = Pet.objects.create(name='fido', owner=owner)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                pet.owner.delete()
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Person)
        self.assertEqual(e.hints, {'instance': owner})

    def test_reverse_fk_delete(self):
        owner = Person.objects.create(name='Someone')
        to_del_qs = owner.pet_set.all()
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                to_del_qs.delete()
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Pet)
        self.assertEqual(e.hints, {'instance': owner})

    def test_reverse_fk_get_or_create(self):
        owner = Person.objects.create(name='Someone')
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                owner.pet_set.get_or_create(name='fido')
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Pet)
        self.assertEqual(e.hints, {'instance': owner})

    def test_reverse_fk_update(self):
        owner = Person.objects.create(name='Someone')
        Pet.objects.create(name='fido', owner=owner)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                owner.pet_set.update(name='max')
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Pet)
        self.assertEqual(e.hints, {'instance': owner})

    def test_m2m_add(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                book.authors.add(auth)
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book.authors.through)
        self.assertEqual(e.hints, {'instance': book})

    def test_m2m_clear(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                book.authors.clear()
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book.authors.through)
        self.assertEqual(e.hints, {'instance': book})

    def test_m2m_delete(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                book.authors.all().delete()
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Person)
        self.assertEqual(e.hints, {'instance': book})

    def test_m2m_get_or_create(self):
        Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                book.authors.get_or_create(name='Someone else')
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book)
        self.assertEqual(e.hints, {'instance': book})

    def test_m2m_remove(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                book.authors.remove(auth)
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book.authors.through)
        self.assertEqual(e.hints, {'instance': book})

    def test_m2m_update(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                book.authors.all().update(name='Different')
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Person)
        self.assertEqual(e.hints, {'instance': book})

    def test_reverse_m2m_add(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                auth.book_set.add(book)
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book.authors.through)
        self.assertEqual(e.hints, {'instance': auth})

    def test_reverse_m2m_clear(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                auth.book_set.clear()
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book.authors.through)
        self.assertEqual(e.hints, {'instance': auth})

    def test_reverse_m2m_delete(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                auth.book_set.all().delete()
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book)
        self.assertEqual(e.hints, {'instance': auth})

    def test_reverse_m2m_get_or_create(self):
        auth = Person.objects.create(name='Someone')
        Book.objects.create(title="Pro Django",
                            published=datetime.date(2008, 12, 16))
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                auth.book_set.get_or_create(title="New Book", published=datetime.datetime.now())
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Person)
        self.assertEqual(e.hints, {'instance': auth})

    def test_reverse_m2m_remove(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                auth.book_set.remove(book)
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book.authors.through)
        self.assertEqual(e.hints, {'instance': auth})

    def test_reverse_m2m_update(self):
        auth = Person.objects.create(name='Someone')
        book = Book.objects.create(title="Pro Django",
                                   published=datetime.date(2008, 12, 16))
        book.authors.add(auth)
        with self.assertRaises(RouterUsed) as cm:
            with self.override_router():
                auth.book_set.all().update(title='Different')
        e = cm.exception
        self.assertEqual(e.mode, RouterUsed.WRITE)
        self.assertEqual(e.model, Book)
        self.assertEqual(e.hints, {'instance': auth})


class NoRelationRouter:
    """Disallow all relations."""
    def allow_relation(self, obj1, obj2, **hints):
        return False


@override_settings(DATABASE_ROUTERS=[NoRelationRouter()])
class RelationAssignmentTests(SimpleTestCase):
    """allow_relation() is called with unsaved model instances."""
    databases = {'default', 'other'}
    router_prevents_msg = 'the current database router prevents this relation'

    def test_foreign_key_relation(self):
        person = Person(name='Someone')
        pet = Pet()
        with self.assertRaisesMessage(ValueError, self.router_prevents_msg):
            pet.owner = person

    def test_reverse_one_to_one_relation(self):
        user = User(username='Someone', password='fake_hash')
        profile = UserProfile()
        with self.assertRaisesMessage(ValueError, self.router_prevents_msg):
            user.userprofile = profile