Python/SQLAlchemy - 更新外键时的加载关系？

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

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    addresses = relationship("Address", back_populates="user")

class Address(Base):
    __tablename__ = 'addresses'
    id = Column(Integer, primary_key=True)
    email_address = Column(String, nullable=False)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship("User", back_populates="addresses")

engine = create_engine('sqlite:///sqlalchemy_example.db')
Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

# 创建一个新用户
user1 = User(name='John Doe')
session.add(user1)
session.commit()

# 创建一个新地址并关联到用户
address1 = Address(email_address='john.doe@example.com', user=user1)
session.add(address1)
session.commit()

# 更新外键关系
user2 = User(name='Jane Doe')
address1.user = user2
session.commit()