In a Node web app, do you open one MongoDB connection for each HTTP request?

Question

I'm adding MongoDB to my Express.js Node web app. This is what I got so far:

// in app.js
var mongodb = require('mongodb');
var mongourl = /* … */;

// These are just examples:

app.get('/write', function (req, res) {
    mongodb.connect(mongourl, function (err, db) {
        db.collection('Users', function (err, coll) {
            coll.insert(/* stuff */, function (err) {
                res.send(200, 'Done.');
            });
        });
    });
});

app.get('/read', function (req, res) {
    mongodb.connect(mongourl, function (err, db) {
        db.collection('Users', function (err, coll) {
            coll.find({}, function (err, cursor) {
                cursor.toArray(function (err, items) {
                    res.send(200, items);   
                });             
            });
        });
    });
});

Assuming that I want to stick with the default mongodb driver (for now):

Is this pattern right? Do I have to open a new connection to the database in each of my different routes that perform database operations?
If the pattern is right, then how do I deal with the obvious code repetition going on here? Obviously, as it stands now, the code is not acceptable.

this will help you. https://stackoverflow.com/questions/38485575/best-way-to-connect-to-mongodb-using-node — Vanshaj Behl, Jun 16 '17 at 06:07

boom · Answer 1 · 2014-01-05T21:35:51.757

2

Use the new standard, MongoClient. It manages the pool for you, defaults to 5.

  //require as a module to be used anywhere.

  module.exports = {}  

  var MongoClient = require('mongodb').MongoClient;
  var mongoURI = /* … */;

  MongoClient.connect(mongoURI, function(err, db) {
    if(err) throw err;

    module.exports.users = db.collection('users');

    console.log('Connected to Mongo!')

  })

then

var db = require('./db.js')

//once connected

//db.users.find()... etc

check out: http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html

pooling details: http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html#connection-pool-configuration

edited Jan 05 '14 at 21:35

answered Jan 05 '14 at 20:45

boom

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So, basically the mongodb API does not support promises? This assign global variable from within async callback doesn't look good. – Šime Vidas Jan 05 '14 at 20:52
What do you mean, it's not global -- but yeah you need to wait for the database to connect before you can use it... – boom Jan 05 '14 at 20:52
The outer scope variable is assigned to from within the inner scope callback. If that's the standard approach, good, but I don't like this pattern. Promises would be better, i.e. `var db = MongoClient.connect(...);`. – Šime Vidas Jan 05 '14 at 20:54
Disagree that promises would be better. – boom Jan 05 '14 at 20:55
Regarding the exporting, how would I export the `db` value which only becomes available in the async callback? – Šime Vidas Jan 05 '14 at 20:56
I also don't see why promises would be better. If you're really strict you can move your Express code (or at least the call to `listen`) into the callback function, but you'd have to do that for promises too. – robertklep Jan 05 '14 at 20:56
@robertklep In my code in the question above, there are four nested callback functions within `.connect()`. That's certainly not the optimal code pattern. Promises fix that. – Šime Vidas Jan 05 '14 at 20:59
@ŠimeVidas yes but we're talking about connection pooling here, which means that the call to `connect` only happens once, during app initialization. From there you can reuse the exported `db` value. – robertklep Jan 05 '14 at 21:01
I put your code inside a db.js file and required it in my app.js: `var db = require('./db');`. Now, when I try to perform `db.collection()`, an error is thrown: `TypeError: Object # – Šime Vidas Jan 05 '14 at 21:18
@boom Yes. I got the `console.log` message and only then did I access the page in the browser. – Šime Vidas Jan 05 '14 at 21:22
@ŠimeVidas working? you could also attach the db object to `module.exports.mongo = db` or something if you need the raw instance. – boom Jan 06 '14 at 14:37
@boom I decided to switch to the "mongojs" module instead. In db.js: `var db = require('mongojs')(/* URL */, ['users']); module.exports = db;`. In app.js: `var db = require('./db');`, and then: `db.users.find(…`. Works and happy with it. – Šime Vidas Jan 06 '14 at 15:05
@ŠimeVidas Same difference, that's just a lib that does this for you. All you would need to do is make the export a function that returns db. My answer is still correct for this question... – boom Jan 06 '14 at 17:32

score 0 · Answer 2 · answered Jan 05 '14 at 20:40

0

Do not close and reopen connection, you're just loosing resources :s

answered Jan 05 '14 at 20:40

farvilain

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Create your connection and store it into a var, like db and reuse it everywhere. – farvilain Jan 05 '14 at 20:41
or create 5, check out connection pooling https://github.com/coopernurse/node-pool – j_mcnally Jan 05 '14 at 20:43
yeah, but begin with only one – farvilain Jan 05 '14 at 20:44
@j_mcnally Wait, why 5? – Šime Vidas Jan 05 '14 at 20:44
concurrency of course. There is still a matter of time where your connection will be blocked finding one persons data, so its best to have a few connections open. – j_mcnally Jan 05 '14 at 20:47
@j_mcnally Uh, I need to learn how to use "node-pool" now? Doesn't the MongoDB driver have this functionality baked in somewhere? – Šime Vidas Jan 05 '14 at 20:50
@ŠimeVidas baked into MongoClient, see my answer. – boom Jan 05 '14 at 20:52
@boom I meant the functionality of multiple concurrent connections. That's baked into `MongoClient`? – Šime Vidas Jan 05 '14 at 21:04
@ŠimeVidas Yeah, you open a db connection once with MongoClient and reuse it across your application. A pool is kept, defaults to 5 connections. – boom Jan 05 '14 at 21:12
@ŠimeVidas http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html#connection-pool-configuration – boom Jan 05 '14 at 21:13

In a Node web app, do you open one MongoDB connection for each HTTP request?

2 Answers2