code: def by_user_names(cls, user_names, db_session=None):
          
          user_names = [(name or "").lower() for name in user_names]
          db_session = get_db_session(db_session)
          query = db_session.query(cls.model)
          query = query.filter(sa.func.lower(cls.model.user_name).in_(user_names))
          # q = q.options(sa.orm.eagerload(cls.groups))
          return query
docs: fetch user objects by user names
  
          :param user_names:
          :param db_session:
          :return: