如何使用Node.js和Mongoose构建后端结构

Question

我在用mongoose作为后端之类的node js中构建代码结构时遇到问题，我需要这样的代码结构，第一个是第二个，第二个是这样。设置代码结构时会感到困惑。

const mongoose = require('mongoose');
const bodyParser = require('body-parser');

const app = express();
app.use(bodyParser.urlencoded({ extended: true }));
app.use(express.json({ extended: false }))
app.use(function (req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
    next();
});


mongoose.connect('URL Something', {
    useNewUrlParser: true
});

const signUpSchema = new mongoose.Schema({
    first_name: String,
    last_name: String,
    password: String,
    email: String,
    phone: String,

})
const User_details = mongoose.model('User_details', signUpSchema)```