如何正确更新表对象(元数据)

考虑以下事项:
我知道要更新定义为:

class MessageBoard(Base):
    __tablename__ = "messageboard"
    id = Column(
        Integer,
        Sequence('messageboard_id', optional=True),
        primary_key=True
    )
    title = Column(Unicode(40), index=True)
    message = Column(UnicodeText())
    to = Column(Unicode(40), index=True)
    # message_type = Column(Unicode(40), index=True) #could be email, sms, or PIMS interface
    created_by = Column(Unicode(40), index=True)
    create_stamp = Column(DateTime(), index=True)
    complete_stamp = Column(DateTime(), index=True)
    status = Column(Unicode(40), index=True)
    # message_type_id = Column(Integer, ForeignKey("board_message_type.id"))
    message_type = relationship(BoardMessageType, secondary=message_type_to_message, lazy="joined", join_depth=2, backref="messageboard")
    agents = relationship(Agents, secondary=agent_message, lazy="joined", join_depth=2, backref="messageboard")

可以更新如下:

s.query(
    MessageBoard
).filter(
    id == 1
).update(
    {"title": "How to update?"}
)

但我不知道如何更新定义如下的表:

agent_message = Table(
    "agent_message",
    Base.metadata,
    Column("agents_id", Integer, ForeignKey("agents.id"), primary_key=True, onupdate="cascade"),
    Column("message_id", Integer, ForeignKey("messageboard.id"), primary_key=True),
    Column("status", Boolean, index=True, default=False) #if READ: True 
)

我尝试过:

q = agent_message.update().where(
    and_(agent_message.c.message_id == read, agent_message.c.agents_id == self.user.agents_id)
).values(
    {"status": True}
)
s.execute(q)

但这会引发一个错误,其中sql语句表示我要更新 agents_id 以及 status :

IntegrityError: (IntegrityError) (1452, 'Cannot add or update a child row: a foreign key constraint fails (`likeminds_prepaid`.`agent_message`, CONSTRAINT `agent_message_ibfk_1` FOREIGN KEY (`agents_id`) REFERENCES `agents` (`id`))', None) u'UPDATE agent_message SET agents_id=?, status=? WHERE agent_message.message_id = ? AND agent_message.agents_id = ?' ('cascade', 1, u'3', 203671L)

可以找到完整堆栈 here

我也在谷歌上搜索了很多,但找不到如何更新上面定义的表并包含多个where子句的示例。。。

更新

我上面的代码有点错误,而不是使用:

s.execute(q)

应该是:

q.execute()