sharing mongodb connection object globally in a node js app

Question

how do i share the db object returned from when i call db.open or db.connect across the entire app?

i have a dbconnect.js module as follows :

var mongodb = require('mongodb');
var global_db  = '';

// Define options. Note poolSize.
var serverOptions = {
   'auto_reconnect': true,
   'poolSize': 5
};

// Now create the server, passing our options.
var serv = new mongodb.Server('localhost', 27017, serverOptions);

// At this point, there is no connection made to the server.

// Create a handle to the Mongo database called 'myDB'.
var dbManager = new mongodb.Db('myDB', serv);

// NOW we initialize ALL 5 connections:
dbManager.open(function (error, db) {
  // Do something with the connection.
  global_db = db;
  // Make sure to call db.close() when ALL connections need
  // to be shut down.
  db.close();
});

function getConnection()
{
   return global_db;
} 

exports.getConnection = getConnection;

and i am using this dbconnect.js in my app.js as:

var http = require('http');
var db = require('./dbconnect').getConnection();
var collection = db.collection('testcollection');
console.log(db);
console.log(collection);

var server = http.createServer();

server.on('request',route);

server.listen(8000,'127.0.0.1');

console.log('Server running at http://127.0.0.1:8000');

function route(request,response)
{
    var url = request.url;
    var doc = {};
    doc[url] = 'ok';
    collection.insert(doc,{w:1},function(err,result)
        {
            if(err) console.log(err);
            else console.log(result);
        });
}

in the console, the db and collection variable show empty values, i also tried removing the db.close() call in dbconnect.js but to no use, however the insertion works when i place it inside dbconnect.js file in the dbManager.open function, how do i do this?or any similar alternatives?

Elephant · Accepted Answer · 2013-03-05 09:31:27Z

2

You can't do that, because dbManager.open( is async method, but you trying to get data from module synchronously.

Try this:

In dbconnect.js

var on_db_ready = null;
module.exports = {
                db_ready:function(db_ready_callback){
                     on_db_ready = db_ready_callback;
                     //here we call callback if already have db
                     if (global_db) on_db_ready(global_db);
                 },
                 getConnection:getConnection
                };
dbManager.open(function (error, db) {
 if (on_db_ready) on_db_ready(db);
  global_db= db;
})

in app.js:

var db = require('./dbconnect').db_ready(function(db){
  //Here i have my database
  //or can use getConnection method
});

this is not very beautiful way, but, I hope, explain your mistake

answered Mar 5, 2013 at 9:31

Elephant

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4 Comments

somedev Over a year ago

Yep, this worked, thanks, what do you mean by not a very beautiful way?How to keep the dbobject cached and pooled if not in this way?

Elephant Over a year ago

I mean that is not elegant\beautiful code. I like creating functions such as "db_ready" through deferred objects. Also usually, after "getDatabase" in mongodb I use "getCollection" method, so I prefer cache collections instead of db's. It makes less and more readable code. Like db_cache.getCollection("users")(function(coll){....});

somedev Over a year ago

ok, i thought of using the same method, but the collections i use are not pre-defined, hence i wanted the db object, but thank you.

Elephant Over a year ago

you can use collections caching without export db from this module. Just request collection in future "getCollection" method inside module, and before returning it - put it to cache. then you can get already existed collection.

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