如何在主server.js中以中间件的形式导出模型，并在单独的model.js文件中写入表的路由

// model.js
const Sequelize = require('sequelize');
const sequelize = new Sequelize('database', 'username', 'password', {
  host: 'localhost',
  dialect: 'mysql',
});

const User = sequelize.define('user', {
  // 定义模型属性
  firstName: {
    type: Sequelize.STRING,
    allowNull: false
  },
  lastName: {
    type: Sequelize.STRING
    // allowNull默认为true
  }
}, {
  // 其他模型选项
});

// 导出模型作为中间件
module.exports = (req, res, next) => {
  req.models = { User };
  next();
};

// server.js
const express = require('express');
const app = express();
const modelMiddleware = require('./model');

// 使用模型中间件
app.use(modelMiddleware);

// 定义路由
app.get('/users', async (req, res) => {
  try {
    const users = await req.models.User.findAll();
    res.json(users);
  } catch (error) {
    res.status(500).send(error.message);
  }
});

// 启动服务器
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});