def create_generic_related_manager(superclass, rel):
    """
    Factory function to create a manager that subclasses another manager
    (generally the default manager of a given model) and adds behaviors
    specific to generic relations.
    """

    class GenericRelatedObjectManager(superclass):
        def __init__(self, instance=None):
            super(GenericRelatedObjectManager, self).__init__()

            self.instance = instance

            self.model = rel.model

            content_type = ContentType.objects.db_manager(instance._state.db).get_for_model(
                instance, for_concrete_model=rel.field.for_concrete_model)
            self.content_type = content_type
            self.content_type_field_name = rel.field.content_type_field_name
            self.object_id_field_name = rel.field.object_id_field_name
            self.prefetch_cache_name = rel.field.attname
            self.pk_val = instance._get_pk_val()

            self.core_filters = {
                '%s__pk' % self.content_type_field_name: content_type.id,
                self.object_id_field_name: self.pk_val,
            }

        def __call__(self, **kwargs):
            # We use **kwargs rather than a kwarg argument to enforce the
            # `manager='manager_name'` syntax.
            manager = getattr(self.model, kwargs.pop('manager'))
            manager_class = create_generic_related_manager(manager.__class__, rel)
            return manager_class(instance=self.instance)
        do_not_call_in_templates = True

        def __str__(self):
            return repr(self)

        def _apply_rel_filters(self, queryset):
            """
            Filter the queryset for the instance this manager is bound to.
            """
            db = self._db or router.db_for_read(self.model, instance=self.instance)
            return queryset.using(db).filter(**self.core_filters)

        def get_queryset(self):
            try:
                return self.instance._prefetched_objects_cache[self.prefetch_cache_name]
            except (AttributeError, KeyError):
                queryset = super(GenericRelatedObjectManager, self).get_queryset()
                return self._apply_rel_filters(queryset)

        def get_prefetch_queryset(self, instances, queryset=None):
            if queryset is None:
                queryset = super(GenericRelatedObjectManager, self).get_queryset()

            queryset._add_hints(instance=instances[0])
            queryset = queryset.using(queryset._db or self._db)

            query = {
                '%s__pk' % self.content_type_field_name: self.content_type.id,
                '%s__in' % self.object_id_field_name: set(obj._get_pk_val() for obj in instances)
            }

            # We (possibly) need to convert object IDs to the type of the
            # instances' PK in order to match up instances:
            object_id_converter = instances[0]._meta.pk.to_python
            return (queryset.filter(**query),
                    lambda relobj: object_id_converter(getattr(relobj, self.object_id_field_name)),
                    lambda obj: obj._get_pk_val(),
                    False,
                    self.prefetch_cache_name)

        def add(self, *objs, **kwargs):
            bulk = kwargs.pop('bulk', True)
            db = router.db_for_write(self.model, instance=self.instance)

            def check_and_update_obj(obj):
                if not isinstance(obj, self.model):
                    raise TypeError("'%s' instance expected, got %r" % (
                        self.model._meta.object_name, obj
                    ))
                setattr(obj, self.content_type_field_name, self.content_type)
                setattr(obj, self.object_id_field_name, self.pk_val)

            if bulk:
                pks = []
                for obj in objs:
                    if obj._state.adding or obj._state.db != db:
                        raise ValueError(
                            "%r instance isn't saved. Use bulk=False or save "
                            "the object first." % obj
                        )
                    check_and_update_obj(obj)
                    pks.append(obj.pk)

                self.model._base_manager.using(db).filter(pk__in=pks).update(**{
                    self.content_type_field_name: self.content_type,
                    self.object_id_field_name: self.pk_val,
                })
            else:
                with transaction.atomic(using=db, savepoint=False):
                    for obj in objs:
                        check_and_update_obj(obj)
                        obj.save()
        add.alters_data = True

        def remove(self, *objs, **kwargs):
            if not objs:
                return
            bulk = kwargs.pop('bulk', True)
            self._clear(self.filter(pk__in=[o.pk for o in objs]), bulk)
        remove.alters_data = True

        def clear(self, **kwargs):
            bulk = kwargs.pop('bulk', True)
            self._clear(self, bulk)
        clear.alters_data = True

        def _clear(self, queryset, bulk):
            db = router.db_for_write(self.model, instance=self.instance)
            queryset = queryset.using(db)
            if bulk:
                # `QuerySet.delete()` creates its own atomic block which
                # contains the `pre_delete` and `post_delete` signal handlers.
                queryset.delete()
            else:
                with transaction.atomic(using=db, savepoint=False):
                    for obj in queryset:
                        obj.delete()
        _clear.alters_data = True

        def set(self, objs, **kwargs):
            # Force evaluation of `objs` in case it's a queryset whose value
            # could be affected by `manager.clear()`. Refs #19816.
            objs = tuple(objs)

            bulk = kwargs.pop('bulk', True)
            clear = kwargs.pop('clear', False)

            db = router.db_for_write(self.model, instance=self.instance)
            with transaction.atomic(using=db, savepoint=False):
                if clear:
                    self.clear()
                    self.add(*objs, bulk=bulk)
                else:
                    old_objs = set(self.using(db).all())
                    new_objs = []
                    for obj in objs:
                        if obj in old_objs:
                            old_objs.remove(obj)
                        else:
                            new_objs.append(obj)

                    self.remove(*old_objs)
                    self.add(*new_objs, bulk=bulk)
        set.alters_data = True

        def create(self, **kwargs):
            kwargs[self.content_type_field_name] = self.content_type
            kwargs[self.object_id_field_name] = self.pk_val
            db = router.db_for_write(self.model, instance=self.instance)
            return super(GenericRelatedObjectManager, self).using(db).create(**kwargs)
        create.alters_data = True

        def get_or_create(self, **kwargs):
            kwargs[self.content_type_field_name] = self.content_type
            kwargs[self.object_id_field_name] = self.pk_val
            db = router.db_for_write(self.model, instance=self.instance)
            return super(GenericRelatedObjectManager, self).using(db).get_or_create(**kwargs)
        get_or_create.alters_data = True

        def update_or_create(self, **kwargs):
            kwargs[self.content_type_field_name] = self.content_type
            kwargs[self.object_id_field_name] = self.pk_val
            db = router.db_for_write(self.model, instance=self.instance)
            return super(GenericRelatedObjectManager, self).using(db).update_or_create(**kwargs)
        update_or_create.alters_data = True

    return GenericRelatedObjectManager
dataset/ETHPy150Open django/django/django/contrib/contenttypes/fields.py/create_generic_related_manager/original