Changes a given `changed_fields` on this object, saves it and returns itself.
        :param update_only_changed_fields: only changed fields will be updated in the database.
        :param changed_fields: fields to change.
        :return: self

def change_and_save(self, update_only_changed_fields=False, **changed_fields):
        """
        Changes a given `changed_fields` on this object, saves it and returns itself.
        :param update_only_changed_fields: only changed fields will be updated in the database.
        :param changed_fields: fields to change.
        :return: self
        """
        change_and_save(self, update_only_changed_fields=update_only_changed_fields, **changed_fields)
        return self