用nodejs删除mongodb中ObjectId类型数据

mongodb中"_id"下面有个ObjectId类型的数据，想通过这个数据把整个对像删除，费了半天劲终于搞定费话少说上代码

 module.exports = function (req, res) {
     var dbCollection = req.app.db.collection('alarm.user');
     var doc          = {};
     if (req.query) {
         doc = req.query;
     }
     var BSON = require('mongodb').BSONPure;
     var obj_id = BSON.ObjectID.createFromHexString(doc._id);

     dbCollection.remove({"_id":obj_id},{safe:true},function(err,result){
         if (err){
              console.log(err);
              res.end('{"error":"remove fail"}');
         }else{
             console.log(result);
             res.end();
         }

     });

 };