如何在异步sqlalchemy中正确处理多对多？

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    roles = relationship('Role', secondary=user_role, back_populates='users')

class Role(Base):
    __tablename__ = 'roles'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    users = relationship('User', secondary=user_role, back_populates='roles')

user_role = Table('user_role', Base.metadata,
    Column('user_id', Integer, ForeignKey('users.id')),
    Column('role_id', Integer, ForeignKey('roles.id'))
)

from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from sqlalchemy.orm import sessionmaker

# 创建异步引擎
engine = create_async_engine('数据库连接字符串')

# 创建异步会话工厂
async_session = sessionmaker(engine, class_=AsyncSession)

async with async_session() as session:
    # 创建用户和角色实例
    user = User(name='John')
    role = Role(name='Admin')

    # 添加多对多关系
    user.roles.append(role)

    # 提交事务
    await session.add(user)
    await session.commit()

async with async_session() as session:
    # 查询用户的角色
    user = await session.query(User).filter(User.name == 'John').first()
    roles = user.roles

    # 查询角色的用户
    role = await session.query(Role).filter(Role.name == 'Admin').first()
    users = role.users