使用flask-restplus在flask-SQLAlchemy中创建多对多关联表时出错

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_restplus import Api, Resource
from sqlalchemy import Table, Column, Integer, ForeignKey
from sqlalchemy.orm import relationship

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'your_database_uri'
db = SQLAlchemy(app)

# 定义关联表
association_table = Table('association', db.Model.metadata,
    Column('left_id', Integer, ForeignKey('left_table.id')),
    Column('right_id', Integer, ForeignKey('right_table.id'))
)

class LeftTable(db.Model):
    __tablename__ = 'left_table'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))
    rights = db.relationship('RightTable', secondary=association_table, backref='lefts')

class RightTable(db.Model):
    __tablename__ = 'right_table'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))

api = Api(app)

@api.route('/lefts')
class LeftResource(Resource):
    def get(self):
        # 处理GET请求的逻辑
        pass

    def post(self):
        # 处理POST请求的逻辑
        pass

@api.route('/rights')
class RightResource(Resource):
    def get(self):
        # 处理GET请求的逻辑
        pass

    def post(self):
        # 处理POST请求的逻辑
        pass

if __name__ == '__main__':
    app.run()