Node js single mongodb connection

Question

I want my entire node application to use one single mongodb connection, at least that's what I think is better. I wrote this little script and want some feedback on it. Especially if what I'm doing makes sense.

This is my mongodb.js file

'use strict';    

// Mongodb module.
var MongoClient = require( 'mongodb' ).MongoClient;    

// Database.
var db;    

// Working variable.
var working;    

// Callbacks array.
var arr = [];    

// Exported variable.
module.exports = function( callBack ) {
    if ( db ) {
        callBack( db );
        return;
    }    

    arr.push( callBack );    

    if ( working ) return;    

    working = true;    

    var MongoDB = MongoClient.connect( 'mongodb://127.0.0.1:27017/test', 
        function( err, res ) {
            if( err ) throw err;    

            console.log( "Connected to MongoDB!" );    

            db = res;    

            for ( var i = 0; i < arr.length; i++ ) { 
                arr[i]( res );
            }    

            arr = [];
        }
    );
}

This is a file where I include the mongodb.js

var collection;
new require( 'mongodb.js' )( 
    function( db ) { 
        collection = db.collection( 'test' ); 
    }
);

Answer 1

If you make your custom callback node style (i.e. function(err, result)), you can simplify this greatly:

'use strict';
var MongoClient = require('mongodb').MongoClient,
    db;


module.exports = function connectToMongo(url, callback) {
    if (db) { callback(null, db); }
    else { 
        MongoClient.connect(url, function(err, conn) {
            db = conn;
            callback(err, conn);
        });
    }
}

And use it:

var connectToMongo = require('./mongodb.js');

/* ... */

connectToMongo('mongodb://127.0.0.1:27017/test', function(err, db) {
    collection = db.collection('test');
});

---

An even better option would be to use Promises. I use bluebird in my projects, but we'll soon have native Promise support (bluebird will probably still be better).

var mongo = require('mongodb'),
    Promise = require('bluebird');

Promise.promisifyAll(mongo);
Promise.promisifyAll(require('mongodb/lib/mongodb/db').Db.prototype);

var db;

module.exports = function connectToMongo(url) {
    if (!db) {
        db = mongo.connectAsync(url); //This returns a promise!
    }
    return db;
};

Then use it like

var connecttoMongo = requiure('./mongodb.js');
connectToMongo('mongodb://127.0.0.1:27017/test').then(function(conn) {
    //Do stuff here
});