Sqlalchemy 设置关系属性会将对象添加到集合关系的会话中。有没有办法阻止这一切？

使用sqlalchemy，如果一个对象具有orm关系属性，并且您创建了该对象的实例，并设置了关系属性，那么您的新对象将添加到设置关系的会话中。e、 g:

from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship, Session
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()
class User(Base):
    __tablename__ = 'users'

    user_id = Column(Integer, primary_key=True)
    name = Column(String)

class Address(Base):
    __tablename__ = 'addresses'

    address_id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey(User.user_id),)
    address = Column(String)

    user = relationship(User, backref='addresses')


engine = create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)
session = Session(bind=engine)

bob = User()
bob.name = 'Bob'
session.add(bob)
session.commit()

bobs_addr = Address()
bobs_addr.user = bob
bobs_addr.address = "23 Bob's st."

# bobs_addr not added to the session

engine.echo = True
session.commit()

运行上述程序的输出：

2011-05-23 12:07:23,461 INFO sqlalchemy.engine.base.Engine.0x...9a10 BEGIN (implicit)
2011-05-23 12:07:23,463 INFO sqlalchemy.engine.base.Engine.0x...9a10 SELECT users.user_id AS users_user_id, users.name AS users_name 
FROM users 
WHERE users.user_id = ?
2011-05-23 12:07:23,463 INFO sqlalchemy.engine.base.Engine.0x...9a10 (1,)
2011-05-23 12:07:23,466 INFO sqlalchemy.engine.base.Engine.0x...9a10 INSERT INTO addresses (user_id, address) VALUES (?, ?)
2011-05-23 12:07:23,466 INFO sqlalchemy.engine.base.Engine.0x...9a10 (1, "23 Bob's st.")
2011-05-23 12:07:23,467 INFO sqlalchemy.engine.base.Engine.0x...9a10 COMMIT

bobs_addr没有添加到会话中，因此我希望它不会提交到db，但是设置bobs_addr.user=bob会导致将bobs_addr添加到会话中。我该如何阻止这种情况发生

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我知道有一种解决方法，那就是设置bobs\u addr.user\u id=bob.user\u id，但我更喜欢使用关系attr。

我认为这可以实现您想要的，但我总是发现默认的cascade='save-update，merge'最有效

user = relationship(User, backref=backref('addresses', cascade=''))

凉的阅读解释了原因。