@classmethod
def set_mongo_replica_set(cls, replica_set=None):
    """
        assigns the MONGO_REPLICA_SET var in config and regenerates mongodb uri

        returns Class
        """
    assert isinstance(replica_set, (str, type(None))
        ), 'database must be a string or NoneType'
    cls.MONGO_REPLICA_SET = replica_set
    cls.generate_mongo_uri()
    return cls
