Removes this list of fields from both the local object and the DB.

def unset_fields(self, fields):
        """ Removes this list of fields from both the local object and the DB. """

        self.mongokat_collection.update_one({"_id": self["_id"]}, {"$unset": {
            f: 1 for f in fields
        }})

        for f in fields:
            if f in self:
                del self[f]