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();
        }
            
    });
  
};