How to reuse mongodb connection in node.js

Question

I\'m using node-mongodb-native driver with mongodb to write a website.

I have a question about how to open mongodb connection once, then use it in collection name us

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

Accepted answer is 3 year old and it wont work with latest node-mongodb-native driver. I have modified @moka answer and added some delay and retry 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);
        });
    }
};