MongoDB Connection Pooling with Node.js Modules
Aug 2, 2015How to implement MongoClient connection pooling in a simple Node.js/MongoDB web app.
Not So Good
Here is a sample node.js app. On a GET request, the app will do something with the database (maybe fetch some data). The database operations are confined in the database.js module, which is great, but a connection with the MongoDB is opened/closed with each operation, which can be costly and inefficient.
app.js
var express = require('express');
var app = express();
var database = require('./database.js');
app.listen(3000);
console.log("Listening on port 3000");
app.get("/", function(req, res) {
// do some stuff
database.doSomethingWithDatabase(someCallback);
});
database.js
var mongodb = require('mongodb');
var MongoClient = mongodb.MongoClient;
var mongoUrl = 'mongodb://127.0.0.1:27017/db_name';
exports.doSomethingWithDatabase = function(callback){
MongoClient.connect(mongoUrl, function(err, db) {
if( err ) throw err;
// connected to db
db.collection('db_name').find({}, function(err, docs) {
// do something
callback(docs);
// close connection to db
db.close();
});
});
};
Better
This is the example on the mongodb github on connection pooling. It’s a great and simple example, but it requires that database operations be within the same module that MongoClient.connect is in to have access to the db variable.
app.js
var express = require('express');
var app = express();
var mongodb = require('mongodb');
var MongoClient = mongodb.MongoClient;
var mongoUrl = 'mongodb://127.0.0.1:27017/db_name';
var db;
// Initialize connection once
MongoClient.connect(mongoUrl, function(err, database) {
if(err) throw err;
db = database;
// Start the application after the database connection is ready
app.listen(3000);
console.log("Listening on port 3000");
});
// Reuse database object in request handlers
app.get("/", function(req, res) {
db.collection('db_name').find({}, function(err, docs) {
// docs found using the same db connection
// do something
});
});
Best
On bigger apps, you’re probably separating your app into several modules by logic. This is the best way to isolate database operations in a database module.
app.js
var express = require('express');
var app = express();
var database = require('./database.js');
// Initialize connection
database.connect(function() {
// Start the application after the database connection is ready
app.listen(3000);
console.log("Listening on port 3000");
app.get("/", function(req, res) {
// do some stuff
database.doSomethingWithDatabase(someCallback);
});
});
database.js
var mongodb = require('mongodb');
var MongoClient = mongodb.MongoClient;
var mongoUrl = 'mongodb://127.0.0.1:27017/db_name';
var db;
exports.connect = function(callback) {
MongoClient.connect(mongoUrl, function(err, database) {
if( err ) throw err;
db = database;
callback();
})
}
exports.doSomethingWithDatabase = function(callback) {
// this is using the same db connection
db.collection('db_name').find({}, function(err, docs) {
// do something
callback(docs);
});
};