Method add

django/db/models/fields/related_descriptors.py:845–880

(self, *objs, bulk=True)

            return queryset, rel_obj_attr, instance_attr, False, cache_name, False

        def add(self, *objs, bulk=True):
            self._check_fk_val()
            self._remove_prefetched_objects()
            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.field.name, self.instance)

            if bulk:
                pks = []
                for obj in objs:
                    check_and_update_obj(obj)
                    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
                        )
                    pks.append(obj.pk)
                self.model._base_manager.using(db).filter(pk__in=pks).update(
                    **{
                        self.field.name: self.instance,
                    }
                )
            else:
                with transaction.atomic(using=db, savepoint=False):
                    for obj in objs:
                        check_and_update_obj(obj)
                        obj.save()

        add.alters_data = True