Node.js 猫鼬是如何出口的？

为什么在导出时不需要指定数据库？ 请解释在这种情况下，如何创建模型并连接数据库

User.js

const {Schema, model} = require('mongoose');
const schema = new Schema({
    email : {type: String, required: true, unique: true},
    password: {type: String, required: true}
});
module.exports = model('User', schema);

app.js

const express = require('express');
const config = require('config');
const mongoose = require('mongoose');

const app = express();

app.use('/api/auth',require('./routes/auth.routes'));

const PORT = config.get('port') || 5000 ;

async function start(){
    try{
        await mongoose.connect(config.get('mongoBase'),{
            useNewUrlParser : true,
            useUnifiedTopology : true,
            useCreateIndex : true
        });
        app.listen(PORT,() => console.log(`app has been started on ${PORT} port`));
    } catch (e) {
        console.log('Server Error', e.message);
        process.exit(1);
    }
}
start();

认证路由

const bcrypt = require('bcrypt');
const User = require('../models/User');
const router = Router();
router.post('/register',
    async (req,res) => {
    try {

       const {email, password} = req.body;

      const candidate =  await User.findOne({ email });
    } catch (e) {
        res.status(500).json({message : 'err'});
    }
    });

在导出器模块中执行mole时会发生什么