python FLASK-SQLAlchemy

第一次使用时出现一些错误，正确的代码

# -*- coding:utf-8 -*-
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+pymysql://root:123456@localhost/pyweb'
app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

db = SQLAlchemy(app)


class Role(db.Model):
    __tablename__ = 'roles'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64), unique=True)
    users = db.relationship('User',backref='role')

    def __repr__(self):
        return '<Role {}>'.format(self.name)


class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), unique=True, index=True)
    role_id = db.Column(db.Integer,db.ForeignKey('roles.id'))

    def __repr__(self):
        return '<User {}>'.format(self.username)



def test():
    # 创建数据库
    db.create_all()
    # 插入行，即创建角色和用户
    admin_role = Role(name='Admin')
    mod_role = Role(name='Moderator')
    user_role = Role(name='User')
    user_john = User(username='john', role=admin_role)
    user_susan = User(username='susan', role=user_role)
    user_david = User(username='david', role=user_role)
    # 准备把对象写入数据库前，先要将其调价到会话中
    db.session.add(mod_role)
    db.session.add(user_role)
    db.session.add(user_john)
    db.session.add(user_susan)
    db.session.add(user_david)
    # 提交会话，写入数据库
    db.session.commit()
    # 修改行
    admin_role.name = 'Administrator'
    db.session.add(admin_role)
    db.session.commit()
    # 删除行
    db.session.delete(mod_role)
    db.session.commit()
    # 查询
    Role.query.all()
    # 使用过滤器，条件查询
    User.query.filter_by(role=user_role).all()


if __name__ == '__main__':
    test()