Node.js开发笔记-20：mongodb 学习

增删改查
https://www.cnblogs.com/ostrich-sunshine/p/6755304.html
MongoDB索引原理
http://www.open-open.com/lib/view/open1461568319242.html

MARK一下
如何使用mongoose对一个100万+的mongodb的表进行遍历操作
https://cnodejs.org/topic/51508570604b3d512113f1b3

var MongoClient = require('mongodb').MongoClient;
var url='mongodb://localhost/sample';
MongoClient.connect(url, function(err, db) {
    if(err) { return console.log("connection failed: %s",err); }
    console.log('connected to mongo, ready for duty work');
    var collection=db.collection('files');
    //setInterval(function(){ console.log('memroy usage : %j',process.memoryUsage());},10000);
    /** fetch all records **/
    var stream=collection.find().stream(),cache=[];
    stream.on('data',function(item){
        cache.push(item);
        if(cache.length==10){
            /** signal mongo to pause reading **/
            stream.pause();
            process.nextTick(function(){
                doLotsWork(cache,function(){
                    cache=[];
                    /** signal mongo to continue, fetch next record **/
                    stream.resume();
                });
            });
        }
    });
    stream.on('end',function(){ console.log('query ended'); });
    stream.on('close',function(){ console.log('query closed'); });
});

function doLotsWork(records,callback){
    //.....do lots of work
    //.....
    //all done, ready to deal with next 10 records
    process.nextTick(function(){
        callback();
    });
}