数据库设计：

db = SQLAlchemy()

roles_users = db.Table(
    'roles_users',
    db.Column('user_id',db.Integer(),db.ForeignKey('users.id')),
    db.Column('role_id',db.Integer(),db.ForeignKey('roles.id'))
)

class Role(db.Model,RoleMixin):
    """创建角色模型类"""
    __tablename__ = 'roles'
 
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64), unique=True)
    description = db.Column(db.String(255))
 
    def __init__(self):
        self.name = name
   

    def __repr__(self):
         return '%r' % self.name
  

class User(db.Model, UserMixin):   
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(30), unique=True)
    email = db.Column(db.String(64), unique=True)
    password = db.Column(db.Text,nullable=False)
    last_login_at = db.Column(db.DateTime, default=datetime.utcnow)
    current_login_at = db.Column(db.DateTime)
    last_login_ip = db.Column(db.String(100))
    current_login_ip = db.Column(db.String(100))
    login_count = db.Column(db.Integer)
    active = db.Column(db.Boolean())
    status = db.Column(db.String(64))
    confirmed_at = db.Column(db.DateTime, default=datetime.now())
    roles = db.relationship('Role',secondary='roles_users',backref=db.backref('users',lazy='dynamic'))

    def __init__(self, name=None, email=None):
        self.name = name
        self.email = email
        self.roles = roles 
   
    def to_json(self):       
        
        json_data = {
            'id': self.id,
            'name': self.name,
            'roles':self.roles,
            'email': self.email,
            'status': self.status,
            'active': self.active, 
            'confirmed_at': self.confirmed_at, 
            'current_login_at': self.current_login_at, 
            'current_login_ip': self.current_login_ip,
            'last_login_at': self.last_login_at, 
            'last_login_ip': self.last_login_ip, 
            'login_count': self.login_count,  
            'status': self.status
        }

        return json_data


    @staticmethod
    def verify_auth_token(token):
        s = Serializer(current_app.config['SECRET_KEY'])
        try:
            data = s.loads(token)
        except SignatureExpired:
            return None # valid token, but expired
        except BadSignature:
            return None # invalid token
        user = User.query.get(data['id'])        
        return user
        
 
 请求返回：
@user.route('/info', methods=['GET', 'POST'])
# @login_required 
def userinfo():
   
    token=request.args.get('token')       
        
    if not token:
        return jsonify({'status':201,'state':0,'msg':'用户不存在'})   
        
    else:
        data = User.verify_auth_token(token)        
        return jsonify({'status':200,'state':1,'msg':'获取用户数据成功','data': data.to_json()})
        

报错： TypeError: Object of type Role is not JSON serializable
为何呢？ 有人遇到吗？