Python django.db.router.allow_relation() Examples

def __set__(self, instance, value):
        if instance is None:
            raise AttributeError("%s must be accessed via instance" % self.related.opts.object_name)

        # The similarity of the code below to the code in
        # ReverseSingleRelatedObjectDescriptor is annoying, but there's a bunch
        # of small differences that would make a common base class convoluted.

        # If null=True, we can assign null here, but otherwise the value needs
        # to be an instance of the related class.
        if value is None and self.related.field.null == False:
            raise ValueError('Cannot assign None: "%s.%s" does not allow null values.' %
                                (instance._meta.object_name, self.related.get_accessor_name()))
        elif value is not None and not isinstance(value, self.related.model):
            raise ValueError('Cannot assign "%r": "%s.%s" must be a "%s" instance.' %
                                (value, instance._meta.object_name,
                                 self.related.get_accessor_name(), self.related.opts.object_name))
        elif value is not None:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": instance is on database "%s", value is on database "%s"' %
                                        (value, instance._state.db, value._state.db))

        related_pk = getattr(instance, self.related.field.rel.get_related_field().attname)
        if related_pk is None:
            raise ValueError('Cannot assign "%r": "%s" instance isn\'t saved in the database.' %
                                (value, instance._meta.object_name))

        # Set the value of the related field to the value of the related object's related field
        setattr(value, self.related.field.attname, related_pk)

        # Since we already know what the related object is, seed the related
        # object caches now, too. This avoids another db hit if you get the
        # object you just set.
        setattr(instance, self.cache_name, value)
        setattr(value, self.related.field.get_cache_name(), instance) 

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_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 allow_relation(self, obj1, obj2, **hints):
        return False 

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 allow_relation(self, obj1, obj2, **hints):
        return False 

def __set__(self, instance, value):
        # The similarity of the code below to the code in
        # ReverseSingleRelatedObjectDescriptor is annoying, but there's a bunch
        # of small differences that would make a common base class convoluted.

        # If null=True, we can assign null here, but otherwise the value needs
        # to be an instance of the related class.
        if value is None and self.related.field.null is False:
            raise ValueError(
                'Cannot assign None: "%s.%s" does not allow null values.' % (
                    instance._meta.object_name,
                    self.related.get_accessor_name(),
                )
            )
        elif value is not None and not isinstance(value, self.related.related_model):
            raise ValueError(
                'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
                    value,
                    instance._meta.object_name,
                    self.related.get_accessor_name(),
                    self.related.related_model._meta.object_name,
                )
            )
        elif value is not None:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)

        related_pk = tuple(getattr(instance, field.attname) for field in self.related.field.foreign_related_fields)
        if None in related_pk:
            raise ValueError(
                'Cannot assign "%r": "%s" instance isn\'t saved in the database.' %
                (value, instance._meta.object_name)
            )

        # Set the value of the related field to the value of the related object's related field
        for index, field in enumerate(self.related.field.local_related_fields):
            setattr(value, field.attname, related_pk[index])

        # Since we already know what the related object is, seed the related
        # object caches now, too. This avoids another db hit if you get the
        # object you just set.
        setattr(instance, self.cache_name, value)
        setattr(value, self.related.field.get_cache_name(), instance) 

def __set__(self, instance, value):
        # If null=True, we can assign null here, but otherwise the value needs
        # to be an instance of the related class.
        if value is None and self.field.null is False:
            raise ValueError(
                'Cannot assign None: "%s.%s" does not allow null values.' %
                (instance._meta.object_name, self.field.name)
            )
        elif value is not None and not isinstance(value, self.field.rel.to):
            raise ValueError(
                'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
                    value,
                    instance._meta.object_name,
                    self.field.name,
                    self.field.rel.to._meta.object_name,
                )
            )
        elif value is not None:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)

        # If we're setting the value of a OneToOneField to None, we need to clear
        # out the cache on any old related object. Otherwise, deleting the
        # previously-related object will also cause this object to be deleted,
        # which is wrong.
        if value is None:
            # Look up the previously-related object, which may still be available
            # since we've not yet cleared out the related field.
            # Use the cache directly, instead of the accessor; if we haven't
            # populated the cache, then we don't care - we're only accessing
            # the object to invalidate the accessor cache, so there's no
            # need to populate the cache just to expire it again.
            related = getattr(instance, self.cache_name, None)

            # If we've got an old related object, we need to clear out its
            # cache. This cache also might not exist if the related object
            # hasn't been accessed yet.
            if related is not None:
                setattr(related, self.field.rel.get_cache_name(), None)

            for lh_field, rh_field in self.field.related_fields:
                setattr(instance, lh_field.attname, None)

        # Set the values of the related field.
        else:
            for lh_field, rh_field in self.field.related_fields:
                setattr(instance, lh_field.attname, getattr(value, rh_field.attname))

        # Since we already know what the related object is, seed the related
        # object caches now, too. This avoids another db hit if you get the
        # object you just set.
        setattr(instance, self.cache_name, value)
        if value is not None and not self.field.rel.multiple:
            setattr(value, self.field.rel.get_cache_name(), instance) 

def __set__(self, instance, value):
        """
        Set the related instance through the reverse relation.

        With the example above, when setting ``place.restaurant = restaurant``:

        - ``self`` is the descriptor managing the ``restaurant`` attribute
        - ``instance`` is the ``place`` instance
        - ``value`` is the ``restaurant`` instance on the right of the equal sign

        Keep in mind that ``Restaurant`` holds the foreign key to ``Place``.
        """
        # The similarity of the code below to the code in
        # ForwardManyToOneDescriptor is annoying, but there's a bunch
        # of small differences that would make a common base class convoluted.

        if value is None:
            # Update the cached related instance (if any) & clear the cache.
            # Following the example above, this would be the cached
            # ``restaurant`` instance (if any).
            rel_obj = self.related.get_cached_value(instance, default=None)
            if rel_obj is not None:
                # Remove the ``restaurant`` instance from the ``place``
                # instance cache.
                self.related.delete_cached_value(instance)
                # Set the ``place`` field on the ``restaurant``
                # instance to None.
                setattr(rel_obj, self.related.field.name, None)
        elif not isinstance(value, self.related.related_model):
            # An object must be an instance of the related class.
            raise ValueError(
                'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
                    value,
                    instance._meta.object_name,
                    self.related.get_accessor_name(),
                    self.related.related_model._meta.object_name,
                )
            )
        else:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)

            related_pk = tuple(getattr(instance, field.attname) for field in self.related.field.foreign_related_fields)
            # Set the value of the related field to the value of the related object's related field
            for index, field in enumerate(self.related.field.local_related_fields):
                setattr(value, field.attname, related_pk[index])

            # Set the related instance cache used by __get__ to avoid an SQL query
            # when accessing the attribute we just set.
            self.related.set_cached_value(instance, value)

            # Set the forward accessor cache on the related object to the current
            # instance to avoid an extra SQL query if it's accessed later on.
            self.related.field.set_cached_value(value, instance) 

def __set__(self, instance, value):
        """
        Set the related instance through the reverse relation.

        With the example above, when setting ``place.restaurant = restaurant``:

        - ``self`` is the descriptor managing the ``restaurant`` attribute
        - ``instance`` is the ``place`` instance
        - ``value`` is the ``restaurant`` instance on the right of the equal sign

        Keep in mind that ``Restaurant`` holds the foreign key to ``Place``.
        """
        # The similarity of the code below to the code in
        # ForwardManyToOneDescriptor is annoying, but there's a bunch
        # of small differences that would make a common base class convoluted.

        if value is None:
            # Update the cached related instance (if any) & clear the cache.
            # Following the example above, this would be the cached
            # ``restaurant`` instance (if any).
            rel_obj = self.related.get_cached_value(instance, default=None)
            if rel_obj is not None:
                # Remove the ``restaurant`` instance from the ``place``
                # instance cache.
                self.related.delete_cached_value(instance)
                # Set the ``place`` field on the ``restaurant``
                # instance to None.
                setattr(rel_obj, self.related.field.name, None)
        elif not isinstance(value, self.related.related_model):
            # An object must be an instance of the related class.
            raise ValueError(
                'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
                    value,
                    instance._meta.object_name,
                    self.related.get_accessor_name(),
                    self.related.related_model._meta.object_name,
                )
            )
        else:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            if value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            if not router.allow_relation(value, instance):
                raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)

            related_pk = tuple(getattr(instance, field.attname) for field in self.related.field.foreign_related_fields)
            # Set the value of the related field to the value of the related object's related field
            for index, field in enumerate(self.related.field.local_related_fields):
                setattr(value, field.attname, related_pk[index])

            # Set the related instance cache used by __get__ to avoid an SQL query
            # when accessing the attribute we just set.
            self.related.set_cached_value(instance, value)

            # Set the forward accessor cache on the related object to the current
            # instance to avoid an extra SQL query if it's accessed later on.
            self.related.field.set_cached_value(value, instance) 

def __set__(self, instance, value):
        """
        Set the related instance through the reverse relation.

        With the example above, when setting ``place.restaurant = restaurant``:

        - ``self`` is the descriptor managing the ``restaurant`` attribute
        - ``instance`` is the ``place`` instance
        - ``value`` is the ``restaurant`` instance on the right of the equal sign

        Keep in mind that ``Restaurant`` holds the foreign key to ``Place``.
        """
        # The similarity of the code below to the code in
        # ForwardManyToOneDescriptor is annoying, but there's a bunch
        # of small differences that would make a common base class convoluted.

        if value is None:
            # Update the cached related instance (if any) & clear the cache.
            try:
                rel_obj = getattr(instance, self.cache_name)
            except AttributeError:
                pass
            else:
                delattr(instance, self.cache_name)
                setattr(rel_obj, self.related.field.name, None)
        elif not isinstance(value, self.related.related_model):
            # An object must be an instance of the related class.
            raise ValueError(
                'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
                    value,
                    instance._meta.object_name,
                    self.related.get_accessor_name(),
                    self.related.related_model._meta.object_name,
                )
            )
        else:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)

            related_pk = tuple(getattr(instance, field.attname) for field in self.related.field.foreign_related_fields)
            # Set the value of the related field to the value of the related object's related field
            for index, field in enumerate(self.related.field.local_related_fields):
                setattr(value, field.attname, related_pk[index])

            # Set the related instance cache used by __get__ to avoid an SQL query
            # when accessing the attribute we just set.
            setattr(instance, self.cache_name, value)

            # Set the forward accessor cache on the related object to the current
            # instance to avoid an extra SQL query if it's accessed later on.
            setattr(value, self.related.field.get_cache_name(), instance) 

def __set__(self, instance, value):
        if instance is None:
            raise AttributeError("%s must be accessed via instance" % self.field.name)

        # If null=True, we can assign null here, but otherwise the value needs
        # to be an instance of the related class.
        if value is None and self.field.null == False:
            raise ValueError('Cannot assign None: "%s.%s" does not allow null values.' %
                                (instance._meta.object_name, self.field.name))
        elif value is not None and not isinstance(value, self.field.rel.to):
            raise ValueError('Cannot assign "%r": "%s.%s" must be a "%s" instance.' %
                                (value, instance._meta.object_name,
                                 self.field.name, self.field.rel.to._meta.object_name))
        elif value is not None:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": instance is on database "%s", value is on database "%s"' %
                                        (value, instance._state.db, value._state.db))

        # If we're setting the value of a OneToOneField to None, we need to clear
        # out the cache on any old related object. Otherwise, deleting the
        # previously-related object will also cause this object to be deleted,
        # which is wrong.
        if value is None:
            # Look up the previously-related object, which may still be available
            # since we've not yet cleared out the related field.
            # Use the cache directly, instead of the accessor; if we haven't
            # populated the cache, then we don't care - we're only accessing
            # the object to invalidate the accessor cache, so there's no
            # need to populate the cache just to expire it again.
            related = getattr(instance, self.cache_name, None)

            # If we've got an old related object, we need to clear out its
            # cache. This cache also might not exist if the related object
            # hasn't been accessed yet.
            if related is not None:
                setattr(related, self.field.related.get_cache_name(), None)

        # Set the value of the related field
        try:
            val = getattr(value, self.field.rel.get_related_field().attname)
        except AttributeError:
            val = None
        setattr(instance, self.field.attname, val)

        # Since we already know what the related object is, seed the related
        # object caches now, too. This avoids another db hit if you get the
        # object you just set.
        setattr(instance, self.cache_name, value)
        if value is not None and not self.field.rel.multiple:
            setattr(value, self.field.related.get_cache_name(), instance) 

def __set__(self, instance, value):
        """
        Set the related instance through the reverse relation.

        With the example above, when setting ``place.restaurant = restaurant``:

        - ``self`` is the descriptor managing the ``restaurant`` attribute
        - ``instance`` is the ``place`` instance
        - ``value`` is the ``restaurant`` instance on the right of the equal sign

        Keep in mind that ``Restaurant`` holds the foreign key to ``Place``.
        """
        # The similarity of the code below to the code in
        # ForwardManyToOneDescriptor is annoying, but there's a bunch
        # of small differences that would make a common base class convoluted.

        if value is None:
            # Update the cached related instance (if any) & clear the cache.
            try:
                rel_obj = getattr(instance, self.cache_name)
            except AttributeError:
                pass
            else:
                delattr(instance, self.cache_name)
                setattr(rel_obj, self.related.field.name, None)
        elif not isinstance(value, self.related.related_model):
            # An object must be an instance of the related class.
            raise ValueError(
                'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
                    value,
                    instance._meta.object_name,
                    self.related.get_accessor_name(),
                    self.related.related_model._meta.object_name,
                )
            )
        else:
            if instance._state.db is None:
                instance._state.db = router.db_for_write(instance.__class__, instance=value)
            elif value._state.db is None:
                value._state.db = router.db_for_write(value.__class__, instance=instance)
            elif value._state.db is not None and instance._state.db is not None:
                if not router.allow_relation(value, instance):
                    raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)

            related_pk = tuple(getattr(instance, field.attname) for field in self.related.field.foreign_related_fields)
            # Set the value of the related field to the value of the related object's related field
            for index, field in enumerate(self.related.field.local_related_fields):
                setattr(value, field.attname, related_pk[index])

            # Set the related instance cache used by __get__ to avoid an SQL query
            # when accessing the attribute we just set.
            setattr(instance, self.cache_name, value)

            # Set the forward accessor cache on the related object to the current
            # instance to avoid an extra SQL query if it's accessed later on.
            setattr(value, self.related.field.get_cache_name(), instance)