MongoDB学习（2）—Node.js与MongoDB的基本连接示例

前提

已经安装了node.js和MongoDB，本文使用的node.js是v0.12.0，MongoDB是3.0.0。

初始化数据

启动MongoDB服务，在test数据库中插入一条实例数据：

db.user.install({name:"scaleworld",age:27});

在Node.js中引入MongoDB模块

npm install mongodb

编写mongodbDemo.js

var mongodb = require('mongodb');
var server = new mongodb.Server("localhost",27017,{safe:true});
new mongodb.Db('test',server,{}).open(function(error,client){
if(error) throw error;
var collection = new mongodb.Collection(client,'user');
collection.find(function(error,cursor){
cursor.each(function(error,doc){
if(doc){
console.log("name:"+doc.name+" age:"+doc.age);
}
});
});
});

运行

{ [Error: Cannot find module '../build/Release/bson'] code: 'MODULE_NOT_FOUND' }

js-bson: Failed to load c++ bson extension, using pure JS version
================================================================================
Please ensure that you set the default write concern for the database by setting    =
=   one of the options                                                                 =
=                                                                                      =
=     w: (value of > -1 or the string 'majority'), where < 1 means                     =
=        no write acknowlegement                                                       =
=     journal: true/false, wait for flush to journal before acknowlegement             =
=     fsync: true/false, wait for flush to file system before acknowlegement           =
=                                                                                      =
=  For backward compatibility safe is still supported and                              =
=   allows values of [true | false | {j:true} | {w:n, wtimeout:n} | {fsync:true}]      =
=   the default value is false which means the driver receives does not                =
=   return the information of the success/error of the insert/update/remove            =
=                                                                                      =
=   ex: new Db(new Server('localhost', 27017), {safe:false})                           =
=                                                                                      =
=   http://www.mongodb.org/display/DOCS/getLastError+Command                           =
=                                                                                      =
=  The default of no acknowlegement will change in the very near future                =
=                                                                                      =
=  This message will disappear when the default safe is set on the driver Db           =
========================================================================================
name:scaleworld age:27

虽然最后打印出了我们之前插入的数据，但是前面一大串的错误还是人看着不舒服，我们要消灭它们。

Error: Cannot find module '../build/Release/bson'的解决办法

{ [Error: Cannot find module '../build/Release/bson'] code: 'MODULE_NOT_FOUND' }

js-bson: Failed to load c++ bson extension, using pure JS version

头两行说的是没有发现bson模块。好办我们立马安装：

npm install bson

然后将D:\nodejsdemo\node_modules\mongodb\node_modules\bson\ext\index.js中的bson = require('../build/Release/bson')改成bson = require('bson') ，重新运行。

不过这样只是解决头两行的问题，还有用=包围起来的问题。

“Please ensure that you set the default write concern for the database”的解决办法

从最后一句话“This message will disappear when the default safe is set on the driver Db”我们就可以看出该问题的解决办法，只要将数据库连接设置为安全即可。

具体代码修改如下：

new mongodb.Db('test',server,{})修改为new mongodb.Db('test',server,{safe:true})