12.MongoDB 设计 CRUD 系统

将 9.CRUD 系统设计 中的案例用 MongoDB 再设计一遍：
app.js

var express = require('express')
var router = require('./router')
var bodyParser = require('body-parser')

var app = express()

app.use('/node_modules', express.static('node_modules'))
app.use('/public', express.static('public'))

app.engine('html',require('express-art-template'))

app.use(bodyParser.urlencoded({ extended: false }))
app.use(bodyParser.json())

app.use(router)

app.listen(3000, function () {
    console.log('running 3000...')
})

router.js

var fs = require('fs')
var crud = require('./crud')

var express = require('express')
var router = express.Router()

router.get('/students', function (req, res) {
    crud.find(function (err, students) {
        if (err) {
            return res.status(500).send('Server error.')
        }
        res.render('index.html', {
            students: students
        })
    })
})

router.get('/students/new', function (req, res) {
    res.render('new.html')
})

router.post('/students/new', function (req, res) {
    new crud(req.body).save(function (err) {
        if(err) {
            return res.status(500).send('Server error.')
        }
        res.redirect('/students')
    })
})

router.get('/students/edit', function (req, res) {
    crud.findById(req.query.id, function (err, student) {
        if(err) {
            return res.status(500).send('Server error.')
        }
        res.render('edit.html', {
            student: student
        })
    })
})

router.post('/students/edit', function (req, res) {
    crud.findByIdAndUpdate(req.body.id, req.body, function (err) {
        if(err) {
            return res.status(500).send('Server error.')
        }
        res.redirect('/students')
    })
})

router.get('/students/delete', function (req, res) {
    crud.deleteById(req.query.id, function (err) {
        if(err) {
            return res.status(500).send('Server error.')
        }
        res.redirect('/students')
    })
})

module.exports = router

crud.js

var mongoose = require('mongoose')

mongoose.connect('mongodb://localhost:27017/test')

var Schema = mongoose.Schema

var studentSchema = new Schema({
    name: {
        type: String,
        required: true
    },
    gender: {
        type: Number,
        enum: [0, 1],
        default: 0
    },
    age: {
        type: Number
    },
    major: {
        type: String
    }
})

module.exports = mongoose.model('Student', studentSchema)