SQLAlchemy的级联删除

我在做在线相册的时候，碰到这么一个需求，1个相册多张图片，1个图片可以被多个用户喜欢，1个用户可以喜欢多个图片。

相册与图片的关系是1：M

图片与用户的关系是N：M

当我想删除这个相册的时候，如果直接删除是会报错的

    sqlalchemy.orm.exc.StaleDataError: DELETE statement on table 'photo_like' expected to delete 1 row(s); Only 0 were matched.

这个时候需要给Photo的喜欢关系添加passive_deletes: 使得其支持关联(被动)删除，设置为True。

 直接上案例，有 A,B,C,AB,AC五张表

    class A(base):

        tablename = "a"

        id = Column(Integer, primary_key=True)

        b = relationship('B', secondary=AB, cascade="delete, delete-orphan", single_parent=True)

        c = relationship('C', secondary=AC, cascade="delete, delete-orphan", single_parent=True)

    class B(base):

        tablename = "b"

        id = Column(Integer, primary_key=True)

        rules = relationship('A', secondary=AB, cascade="delete, delete-orphan", single_parent=True, passive_deletes=True)

    class C(base):

        tablename = "c"

        id = Column(Integer, primary_key=True)

        rules = relationship('A', secondary=AC, cascade="delete, delete-orphan", single_parent=True, passive_deletes=True)

    AB = Table(

        "AB", Base.metadata,

        Column("A_id", Integer, ForeignKey("A.id")),

        Column("B_id", Integer, ForeignKey("B.id"))

    )

    AC = Table(

        "AC", Base.metadata,

        Column("A_id", Integer, ForeignKey("A.id")),

        Column("C_id", Integer, ForeignKey("C.id"))

    )




关系是：

    A表对B表多对多，关系存放在AB表

    A表对C表多对多，关系存放在AC表

操作：

    删除A表的数据时，同时删除B,C,AB,AC表与A相关联的数据。

secondary：多对多关联类

cascade：设置级联关系，删除用delete, delete-orphan

single_parent：让级联支持多对多，设置为True

没有此属性会报异常：On X.x, delete-orphan cascade is not supported on a many-to-many or many-to-one relationship when single_parent is not set. Set single_parent=True on the relationship().

passive_deletes: 支持关联(被动)删除，设置为True

没有此属性会报异常：DELETE statement on table 'B' expected to delete 1 row(s); Only 0 were matched.