How to reuse mongodb connection in node.js

Question

I am using the node-mongodb-native driver with mongodb to create a website.

I have a question on how to open a mongodb connection once and then use it in collection usernames in user.js and messages with collection names in comment.js

I want to open a db connection in db.js , then insert / save data for users and message collections

Currently the code is my db.js

 var Db = require('mongodb').Db, Connection = require('mongodb').Connection, Server = require('mongodb').Server; module.exports = new Db( 'blog', new Server('localhost', Connection.DEFAULT_PORT, {auto_reconnect: true}) ); 

I used db.js in user.js as follows

 var mongodb = require('./db'); function User(user){ this.name = user.name; this.password = user.password; this.email = user.email; }; module.exports = User; User.prototype.save = function(callback) {//save user information //document to save in db var user = { name: this.name, password: this.password, email: this.email }; mongodb.close(); //open mongodb database mongodb.open(function(err, db){ if(err){ return callback(err); } //read users collection db.collection('users', function(err, collection){ if(err){ mongodb.close(); return callback(err); } //insert data into users collections collection.insert(user,{safe: true}, function(err, user){ mongodb.close(); callback(err, user);//success return inserted user information }); }); }); }; 

and comment.js

 var mongodb = require('./db'); function Comment(name, day, title, comment) { this.name = name; this.day = day; this.title = title; this.comment = comment; } module.exports = Comment; Comment.prototype.save = function(callback) { var name = this.name, day = this.day, title = this.title, comment = this.comment; mongodb.open(function (err, db) { if (err) { return callback(err); } db.collection('posts', function (err, collection) { if (err) { mongodb.close(); return callback(err); } //depend on name time and title add comment collection.findAndModify({"name":name,"time.day":day,"title":title} , [ ['time',-1] ] , {$push:{"comments":comment}} , {new: true} , function (err,comment) { mongodb.close(); callback(null); }); }); }); }; 

Answer 1

You can connect once and then reuse it as many times as you want:

 var mongodb = require('mongodb'); var events = require('events'); var event = new events.EventEmitter(); var access = new mongodb.Server(host, port, { }); var client = null; new mongodb.Db('YOUR DATABASE', access, { safe: true, auto_reconnect: true }).open(function (err, c) { if (!err) { client = c; console.log('database connected'); event.emit('connect'); } else { console.log('database connection error', err); event.emit('error'); } }); exports.get = function(fn) { if(client) { fn(client); } else { event.on('connect', function() { fn(client); }); } }; 

And then reuse it:

 var db = require('./db'); var items; db.get(function(client) { items = new mongodb.Collection(client, 'collection'); }); // then anywhere in your code db.get(function() { // items.find({ ... }); 

Answer 2

The accepted answer is 3 years and it will not work with the latest node-Mongodb driver. I modified @moka's answer and added delay and repeat logic.

 var MongoClient = require('mongodb').MongoClient; var events = require('events'); var event = new events.EventEmitter(); var database = null; var retries = 0; var delay = 300; setTimeout(connect,delay); // Use connect method to connect to the server function connect(){ MongoClient.connect(process.env.MONGODB_URL, function(err, db) { if(!err){ console.log("Connected successfully to server"); database = db; event.emit('dbconnect'); } else { if(retries < 4){ console.log('Retrying to connect db %s', retries++); setTimeout(connect,delay); } else { console.log('Unable to connect db'); } } }); } exports.get = function(fn) { if(database !== null) { fn(database); } else { event.on('dbconnect', function() { fn(database); }); } };