SQLAlchemy：具有一对一关系的联接继承

Question

我正在尝试使用SQLAlchemy的joined inheritance结构来完成以下one-to-one relationship：Box和Item都是Element和{{1 }}有一个Box。

类定义如下：

Item

当我尝试实例化class Element(Base): __tablename__ = 'element' id = Column(Integer, primary_key=True) el_type = Column(String) __mapper_args__ = dict( polymorphic_identity='element', polymorphic_on=el_type, ) class Box(Element): # Joined table inheritance: Element. __tablename__ = 'box' id = Column(Integer, ForeignKey('element.id'), primary_key=True) __mapper_args__ = dict(polymorphic_identity='box') # One-to-one relationship: Item. item = relationship('Item', back_populates='box', uselist=False) def __init__(self, item_name=None): self.item = Item(item_name) class Item(Element): # Joined table inheritance: Element. __tablename__ = 'item' id = Column(Integer, ForeignKey('element.id'), primary_key=True) __mapper_args__ = dict(polymorphic_identity='item') # One-to-one relationship: Box. box_id = Column(Integer, ForeignKey('box.id')) box = relationship('Box', back_populates='item') name = Column(String) def __init__(self, name): self.name = name 时，我得到：

b = Box('rock')

现在，我进入了SQLAlchemy的page on this issue（我可能会添加很棒的文档），但是我不确定如何弥合他们的示例与我的情况之间的鸿沟。我认为这可能会解决问题：

sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship Box.item - 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.

...但是我遇到了同样的错误。

我在做什么错了？

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更新：

我现在尝试使用ForeignKeyConstraint构造，以便更明确地向SQLAlchemy描述所需的行为；无济于事：

class Item(Element):
    # ...
    box = relationship('Box',
        back_populates='item', foreign_keys=[id, box_id])
    # ...

一个简单的class Box(Element): # ... id = Column(Integer, primary_key=True) # ... ForeignKeyConstraint([id], ['element.id']) # ... class Item(Element): # ... id = Column(Integer, primary_key=True) # ... # One-to-one relationship: Box. box_id = Column(Integer) box = relationship('Box', back_populates='item') ForeignKeyConstraint([id, box_id], ['element.id', 'box.id']) # ... 被扔给我（没有描述）。鉴于SQLAlchemy在产生有意义的错误消息方面拥有良好的记录，这是否表明这是意料之外的情况？