Python sqlalchemy一对多关系，其中该外键在模型中使用两次

我有这样一个简单的模型

class ChatMessage(Base):
    __tablename__ = 'chat_messages'
   id = Column(Integer, ForeignKey('messages.id'))
   sender_id = Column(Integer, ForeignKey('users.id'))
   receiver_id = Column(Integer, ForeignKey('users.id'))

我尝试添加与用户相关的消息

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String, nullable=False)
    chat_messages = relationship("ChatMessage", backref="participants",
                             foreign_keys="[ChatMessage.sender_id, ChatMessage.receiver_id]")

它给出：

---

InvalidRequestError:一个或多个映射程序未能初始化-无法继续初始化其他映射程序。最初的异常是：无法确定relationship User.chat_消息上的父/子表之间的联接条件-有多个外键路径链接这些表。指定'foreign_keys'参数，提供那些应被视为包含父表外键引用的列的列表。

定义primaryjoin似乎有点帮助，只是append现在不起作用

class User(Backend.instance().get_base()):

   __tablename__ = 'users'

    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String, nullable=False)
    chat_messages = relationship("ChatMessage", backref="participants",
                             primaryjoin="User.id==ChatMessage.sender_id or User.id==ChatMessage.receiver_id")

---

看起来定义primaryjoin有点帮助，只是append现在不起作用

class User(Backend.instance().get_base()):

   __tablename__ = 'users'

    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String, nullable=False)
    chat_messages = relationship("ChatMessage", backref="participants",
                             primaryjoin="User.id==ChatMessage.sender_id or User.id==ChatMessage.receiver_id")

---

在创建两个类后设置特殊关系

import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship, backref

engine = sa.create_engine('sqlite:///test.db', echo=True)
Session = sessionmaker(bind=engine)
Base = declarative_base(bind=engine)


class User(Base):
    __tablename__ = 'users'
    id = sa.Column(sa.Integer, primary_key=True)


class ChatMessage(Base):
    __tablename__ = 'chat_messages'
    id = sa.Column(sa.Integer, primary_key=True)
    sender_id = sa.Column(sa.Integer, sa.ForeignKey(User.id))
    receiver_id = sa.Column(sa.Integer, sa.ForeignKey(User.id))
    content = sa.Column(sa.String, nullable=False)

    __table_args__ = (
        sa.CheckConstraint(receiver_id != sender_id),
    )

    sender = relationship(User, foreign_keys=sender_id, backref='sent_chat_messages')
    receiver = relationship(User, foreign_keys=receiver_id, backref='received_chat_messages')


User.chat_messages = relationship(ChatMessage, primaryjoin=sa.or_(
    User.id == ChatMessage.sender_id,
    User.id == ChatMessage.receiver_id
), backref=backref('participants', uselist=True, viewonly=True), viewonly=True)

---

之所以使用

viewonly=True

，是因为此关系使用自定义联接，并且如果数据发生更改，SQLAlchemy不知道该怎么办。例如，如果附加到参与者，它会将用户添加为发送者还是接收者？

在创建这两个类后设置特殊关系

import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship, backref

engine = sa.create_engine('sqlite:///test.db', echo=True)
Session = sessionmaker(bind=engine)
Base = declarative_base(bind=engine)


class User(Base):
    __tablename__ = 'users'
    id = sa.Column(sa.Integer, primary_key=True)


class ChatMessage(Base):
    __tablename__ = 'chat_messages'
    id = sa.Column(sa.Integer, primary_key=True)
    sender_id = sa.Column(sa.Integer, sa.ForeignKey(User.id))
    receiver_id = sa.Column(sa.Integer, sa.ForeignKey(User.id))
    content = sa.Column(sa.String, nullable=False)

    __table_args__ = (
        sa.CheckConstraint(receiver_id != sender_id),
    )

    sender = relationship(User, foreign_keys=sender_id, backref='sent_chat_messages')
    receiver = relationship(User, foreign_keys=receiver_id, backref='received_chat_messages')


User.chat_messages = relationship(ChatMessage, primaryjoin=sa.or_(
    User.id == ChatMessage.sender_id,
    User.id == ChatMessage.receiver_id
), backref=backref('participants', uselist=True, viewonly=True), viewonly=True)

之所以使用

viewonly=True

，是因为此关系使用自定义联接，并且如果数据发生更改，SQLAlchemy不知道该怎么办。例如，如果附加到参与者，它会将用户添加为发送者还是接收者