使用flask_sqlalchemy创建多对多关系

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

# 用户模型类
class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))
    roles = db.relationship('Role', secondary='user_role', backref='users')

# 角色模型类
class Role(db.Model):
    __tablename__ = 'roles'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))

# 中间表模型类
class UserRole(db.Model):
    __tablename__ = 'user_role'
    user_id = db.Column(db.Integer, db.ForeignKey('users.id'), primary_key=True)
    role_id = db.Column(db.Integer, db.ForeignKey('roles.id'), primary_key=True)

from flask import Flask

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = '数据库连接字符串'
db.init_app(app)

with app.app_context():
    db.create_all()

user1 = User(name='User1')
user2 = User(name='User2')
role1 = Role(name='Role1')
role2 = Role(name='Role2')

user1.roles.append(role1)
user1.roles.append(role2)
user2.roles.append(role2)

db.session.add(user1)
db.session.add(user2)
db.session.commit()

user = User.query.filter_by(name='User1').first()
roles = user.roles

role = Role.query.filter_by(name='Role2').first()
users = role.users