nodejs(express)链接操作mongodb

1.安装mongodb数据库，官网下载地址：https://www.mongodb.com/download-center#community

2.官方推荐node-mongodb-native来操作mongodb，实际开发中估计更多会选用类似mongoose的模块来操作来提升开发效率,mongoose安装：

npm install -g mongoose –save(-g表示全局，–save存储到本地) 
3.创建一个链接： 
db.js

var mongoose = require('mongoose'), DB_URL = 'mongodb://localhost:27017/dbname';

mongoose.connect(DB_URL);//创建链接

  * 连接成功
  */
mongoose.connection.on('connected', function () {    
    console.log('Mongoose connection open to ' + DB_URL);  
});    

/**
 * 连接异常
 */
mongoose.connection.on('error',function (err) {    
    console.log('Mongoose connection error: ' + err);  
});    

/**
 * 连接断开
 */
mongoose.connection.on('disconnected', function () {    
    console.log('Mongoose connection disconnected');  
}); 
module.exports = mongoose;//暴露出去链接的对象