Python SQLAlchemy级联删除多对多关系

在多对多关系上定义删除级联的正确方法是什么

试图实现这样一种设置，即只删除一个用户将删除用户以及存储在'user\u favorited'中的关系

不同的场景导致用户+关系和用户偏好/偏好被删除

    class User(Base):
        __tablename__ = 'user'
        id = Column(Integer, primary_key=True)
        username = Column(String(30), nullable=False, unique=True, index=True)

        favorites = relationship("User", secondary='user_favorited',
            primaryjoin=UserFavorited.user_id==id,
            secondaryjoin=UserFavorited.favorite_user_id==id,
            backref=backref('favorites_list', lazy='dynamic', cascade='all,delete-orphan'),
            cascade="all",
            order_by=UserFavorited.favorited_on.desc())

        favorited_by = relationship("User", secondary='user_favorited',
            primaryjoin=UserFavorited.favorite_user_id==id,
            secondaryjoin=UserFavorited.user_id==id,
            backref=backref('favorited_list', lazy='dynamic', cascade='all,delete-orphan'),
            cascade="all",
            order_by=UserFavorited.favorited_on.desc())


   class UserFavorited(Base):
       __tablename__ = 'user_favorited'
       user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
       favorite_user_id = Column(Integer, ForeignKey('user.id'), primary_key=True, index=True)
       favorited_on = Column(DateTime(timezone=True), nullable=False)

增加复杂性的是可以添加到关系和backref中的以下参数

• 单亲
• 仅查看（）

目标： 第一个用户的删除不应导致第二个用户的删除。只应删除第一个用户和关系

    class User(Base):
        __tablename__ = 'user'
        id = Column(Integer, primary_key=True)
        username = Column(String(30), nullable=False, unique=True, index=True)

        favorites = relationship("User", secondary='user_favorited',
            primaryjoin=UserFavorited.user_id==id,
            secondaryjoin=UserFavorited.favorite_user_id==id,
            backref=backref('favorites_list', lazy='dynamic', cascade='all,delete-orphan'),
            cascade="all",
            order_by=UserFavorited.favorited_on.desc())

        favorited_by = relationship("User", secondary='user_favorited',
            primaryjoin=UserFavorited.favorite_user_id==id,
            secondaryjoin=UserFavorited.user_id==id,
            backref=backref('favorited_list', lazy='dynamic', cascade='all,delete-orphan'),
            cascade="all",
            order_by=UserFavorited.favorited_on.desc())


   class UserFavorited(Base):
       __tablename__ = 'user_favorited'
       user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
       favorite_user_id = Column(Integer, ForeignKey('user.id'), primary_key=True, index=True)
       favorited_on = Column(DateTime(timezone=True), nullable=False)