之前使用了基于koa2的MVC结构的 egg 框架，大概理解是egg的使用规范。所以这里我们也简单的实现基于koa2的MVC结构。
目录结构为：

mvc的基本加载流程也是：

koa2 --> app --> 引入config ---> 引入model ---> 引入server ---> 引入controller ---> 实列化 ---> 挂载到ctx ---> ctx全局使用复制代码

以上就是mvc基本的思路。下边来看核心代码：

//cegg.js 
const Koa = require('koa');
const Router = require('koa-router'); 
const routerModel = require('./router');
const { initController, initServer, initModel } = require('./loader');
class cf{   
     constructor(){        
        this.app = new Koa();       
        initModel(this);        
        initServer(this);        
        initController(this);        
        const Server = this.servers;        
        const Controller = this.controllers;        
        this.app.use(async (ctx, next) => {            
            ctx.Server = Server;            
            await next();        
        });        
        const router = new Router();        
        const routerObj = routerModel({ Server, Controller, router });                
        this.app.use(routerObj.routes()).use(routerObj.allowedMethods());    
     }    

     start(port){        
        this.app.listen(port, ()=>{            
            console.log('server is starting........!');        
        });    
    }
}
module.exports = new cf();复制代码

以上是koa2 的 http 服务实现，服务ctx的挂载。

const path = require('path');
const fs = require('fs');
const Sequelize = require('sequelize');

function load(dir, fn){    
        const url = path.resolve(__dirname, dir);    
        const files = fs.readdirSync(url);    
        files.forEach(file => {        
            if(file.endsWith('.js')){            
                const filename = file.replace('.js', '');            
                const fileModel = require(url+'/'+filename);            
                fn(filename, fileModel);        
            }    
        });
 }

function initController(app){    
        app.controllers = {};    
        load('../controller', (filename, controller)=>{        
            app.controllers[filename] = new controller();    
        });    
        return app;
}

function initServer(app){    
        app.servers = {};    
        load('../server', (filename, server)=>{        
            app.servers[filename] = new server(app.models);    
        });    
        return app;
}

function initModel(app){    
        load('../config', (filename, config) => {        
            app.models = {};        
            load('../model', (filename, model)=>{            
                const sequelize = new Sequelize(config.db);            
                app.models[filename] = model({ sequelize, Sequelize });        
            });        
         return app;    
    })   
}
module.exports = { initController, initServer, initModel };复制代码

以上是controller，server, model 的文件加载

module.exports = app => {      
    const { Controller, router } = app;    
    router.get('/', Controller.home.home);    
    return router;
}复制代码

路由及对应的controller方法。对以上mvc的应用。

//controller/home.js
class home{    
    async home(ctx, next){        
        const res = await ctx.Server.server.userInfo();        
        ctx.body = res;    
}}
module.exports = home;

//server/server.js
class server{    
        constructor(model){        
            this.model = model;   
         }

    async userInfo(){        
        try{            
            return this.model.User.findAll();        
        }catch(error){            
            console.log(error);        
        }    
}}
module.exports = server;

//model/user.js
module.exports = app => {    
    const { sequelize, Sequelize } = app;     
    const User = sequelize.define('user',{        
        id: {            
            type: Sequelize.INTEGER,            
            autoIncrement: true,            
            allowNull: false,            
            primaryKey: true,            
            unique: true        
        },       
        username: {            
            type: Sequelize.STRING,            
            field: 'username'         
        },        
        email:{            
            type: Sequelize.STRING        
        }    
   },{        
        freezeTableName: true    
   });    
    return User;
};复制代码

这样就是实现对数据的访问了。

以上就是我自己对koa2实现mvc自己的思路和理解，同时向egg致敬，也欢迎各路大神指正和批评。完整请查看 github