如何在SQLAlchemy模型的构造器中通过关系来存储数据？

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

Base = declarative_base()

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

class Post(Base):
    __tablename__ = 'posts'
    id = Column(Integer, primary_key=True)
    title = Column(String)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship('User', back_populates='posts')

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

engine = create_engine('数据库连接字符串')
Session = sessionmaker(bind=engine)
session = Session()

user = User(name='John')
post1 = Post(title='Post 1', user=user)
post2 = Post(title='Post 2', user=user)

session.add(user)
session.commit()