python - 具有一对多关系的 SQLAlchemy 关系错误

Question

所以我在 SQLAlchemy (0.8) 中有这种一对多的关系:

class Parent(Base):

    __tablename__ = "parents"

    cid = Column(Integer(11), primary_key = True, autoincrement = False)
    uid = Column(Integer(11), ForeignKey('otherTable.uid',
           ondelete = 'CASCADE'), primary_key = True)
    ...

    # Relationship with child
    childs_rel = relationship("Child", backref = 'parents', 
                              cascade = "all, delete-orphan")

和

class Child(Base):

    __tablename__ = "childs"

    mid = Column(Integer(11), primary_key = True, autoincrement = False)
    cid = Column(Integer(11), ForeignKey('parents.cid',
           ondelete = 'CASCADE'), primary_key = True)
    uid = Column(Integer(11), ForeignKey('parents.uid',
           ondelete = 'CASCADE'), primary_key = True)
    ...

我可以创建这个数据库，但是当我试图操作它时，我得到了这个错误:

sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship Parent.childs_rel - there are multiple foreign key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.

我试图在 childs_rel 中指定“foreign_keys”，但它说父类中没有外键，这是真的......必须在子类中指定但根据 SQLAlchemy 的 ORM 文档，关系已定义在“一对多”关系中的“一”...

http://docs.sqlalchemy.org/en/rel_0_8/orm/relationships.html#one-to-many

你认为这里发生了什么？非常感谢!

Answer 1

我想我知道这里发生了什么:

Note that you cannot define a “composite” foreign key constraint, that is a constraint between a grouping of multiple parent/child columns, using ForeignKey objects. To define this grouping, the ForeignKeyConstraint object must be used, and applied to the Table. The associated ForeignKey objects are created automatically.

对不起各位。无论如何，谢谢! :D

编辑:这是我为需要它的人提供的解决方案:

class Child(Base):

    __tablename__ = "childs"

    mid = Column(Integer(11), primary_key = True, autoincrement = False)
    cid = Column(Integer(11), primary_key = True)
    uid = Column(Integer(11), primary_key = True)

    __table_args__ = (ForeignKeyConstraint([cid, uid], [Parent.cid, Parent.uid]), {})