Handle mongodb connection in expressJS

Question

im using expressJS and mongoDB and I try to persist my mongodb connection opened in one place to whole app.

How should I do it?

I dont want to open it every time in my every route/model file, which looks like:

moods.js (example file, i have plenty of them, one for every collection)

exports.findAll = function(req, res) {
    db.collection('moods', function(err, collection) {
        collection.find().toArray(function(err, items) {
            res.send(items);
        });
    });
};

 .... some other methods

and main app.js file:

var express = require('express');
var routes = require('./routes');
var mood = require('./routes/moods');


var http = require('http');
var path = require('path');

var app = express();


// all environments
app.set('port', process.env.PORT || 3000);
app.set('views', __dirname + '/views');
app.set('view engine', 'hjs');
app.use(express.favicon());
...

app.get('/moods', mood.findAll);

....
http.createServer(app).listen(app.get('port'), function(){
  console.log('Express server listening on port ' + app.get('port'));
});

Now, where should I put this piece of code to exist once and work for my every collection files? I mean to open one coonnection, not opening new every time i want to query my DB.

         var mongodb = require('mongodb');
         var db = new mongodb.Db('xxxx',
           new mongodb.Server('xxxx', 10059, {})
         );
         db.open(function (err, db_p) {
           if (err) { throw err; }
           db.authenticate('xxxx', 'xxxx', function (err, replies) {
             // You are now connected and authenticated.
           });
         });

Answer 1

You've got several reasonable options. It's really a matter of personal preference.

Create another module that opens the connection and have all other modules use that module:

mongo_connection.js

In that file, you'll put the connection and authentication code. Export the db instance for example:

exports.db = db;

In other files, you could require it:

var connection = require('./mongo_connection.js');
var db = connection.db;

Or, I often create the connection once (in a module), and then pass that to an initialization function in routes:

var users = require('./routes/users.js');
users.initialize(db);

I often do that as there's other common configuration work and settings that I want to provide to the routes:

var initialize = function(app, config) {

};

If you pass the express app instance around, you could set it as well:

app.set('mongo', db);

And then use app.get('mongo') to fetch it.

Answer 2

You can use express-mongo-db middleware for this. It will create and cache connection to mongodb so you can use it inside findAll through req.db property.