code: def all(cls, klass, db_session=None):
          
          db_session = get_db_session(db_session)
          return db_session.query(klass)
docs: returns all objects of specific type - will work correctly with
          sqlalchemy inheritance models, you should normally use models
          base_query()  instead of this function its for bw. compat purposes
  
          :param klass:
          :param db_session:
          :return: