,function(err,client){
if(err){
console.log("失败");
}else{
//指定数据库的名字...,
* arr:插入的文档
* cb:回调函数。...(collection).findOne({_id: mongodb.ObjectId(id)}, function (err, results) {
cb(err, results...(collection).updateOne({_id:mongodb.ObjectId(id)}, upObj, function (err, results) {
cb(err...db.collection(collection).deleteOne({_id: mongodb.ObjectId(id)}, function (err, results) {