Removed some now dead code from deletion (thanks to Carl Meyer for noticing it).

        self.using = using

        # Initially, {model: set([instances])}, later values become lists.

        self.data = {}

        self.batches = {} # {model: {field: set([instances])}}

        self.field_updates = {} # {model: {(field, value): set([instances])}}

        # fast_deletes is a list of queryset-likes that can be deleted without

        # fetching the objects into memory.

                source._meta.concrete_model, set()).add(model._meta.concrete_model)

        return new_objs

    def add_batch(self, model, field, objs):

        """

        Schedules a batch delete. Every instance of 'model' that is related to

        an instance of 'obj' through 'field' will be deleted.

        """

        self.batches.setdefault(model, {}).setdefault(field, set()).update(objs)

    def add_field_update(self, field, value, objs):

        """

        Schedules a field update. 'objs' must be a homogenous iterable

        for instances in six.itervalues(self.data):

            instances.reverse()

        # delete batches

        for model, batches in six.iteritems(self.batches):

            query = sql.DeleteQuery(model)

            for field, instances in six.iteritems(batches):

                query.delete_batch([obj.pk for obj in instances], self.using, field)

        # delete instances

        for model, instances in six.iteritems(self.data):

            query = sql.DeleteQuery(model)