SQLAlchemy - 四个表之间的关系？

Question

这是我的设置：

class User(Base):
    __tablename__ = 'users'
    user_id = Column(Integer, primary_key=True)

class Object(Base):
    __tablename__ = 'objects'
    object_id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey('User.user_id'))

class ObjectHistory(Base):
    __tablename__ = 'object_histories'
    history_id = Column(Integer, primary_key=True)
    object_id = Column(Integer, primary_key=True)

class Action(Base):
    __tablename__ = 'actions'
    action_id = Column(Integer, primary_key=True)

class ActionDetail(Base):
    __tablename__ = 'action_details'
    detail_id = Column(Integer, primary_key=True)
    history_id = Column(Integer, ForeignKey('ObjectHistory.id')

    object = relationship('Object', secondary='object_histories',
                          primaryjoin='ActionDetail.history_id==ObjectHistory.history_id',
                          secondaryjoin='Object.object_id==ObjectHistory.object_id',
                          backref='action_details')

    user = relationship('User', ????, backref='action_details')

如何在ActionDetail上创建user关系？可能吗？我尝试过类似上面object关系的东西，但无济于事。