What is best way to handle global connection of Mongodb in NodeJs

Question

I using Node-Mongo-Native and trying to set a global connection variable, but I am confused between two possible solutions. Can you guys help me out with which one would be the good one? 1. Solution ( which is bad because every request will try to create a new connection.)

var express = require('express');   var app = express();   var MongoClient = require('mongodb').MongoClient;   var assert = require('assert');  // Connection URL var url = '[connectionString]]';  // start server on port 3000 app.listen(3000, '0.0.0.0', function() {     // print a message when the server starts listening   console.log("server starting"); });  // Use connect method to connect to the server when the page is requested app.get('/', function(request, response) {     MongoClient.connect(url, function(err, db) {     assert.equal(null, err);     db.listCollections({}).toArray(function(err, collections) {         assert.equal(null, err);         collections.forEach(function(collection) {             console.log(collection);         });         db.close();     })     response.send('Connected - see console for a list of available collections');   }); }); 

2. Solution ( to connect at app init and assign the connection string to a global variable). but I believe assigning connection string to a global variable is a not a good idea.

   var mongodb; var url = '[connectionString]'; MongoClient.connect(url, function(err, db) {
   assert.equal(null, err); mongodb=db; } );

I want to create a connection at the app initialization and use throughout the app lifetime.

Can you guys help me out? Thanks.

Answer 1

Create a Connection singleton module to manage the apps database connection.

MongoClient does not provide a singleton connection pool so you don't want to call MongoClient.connect() repeatedly in your app. A singleton class to wrap the mongo client works for most apps I've seen.

const MongoClient = require('mongodb').MongoClient  class Connection {      static async open() {         if (this.db) return this.db         this.db = await MongoClient.connect(this.url, this.options)         return this.db     }  }  Connection.db = null Connection.url = 'mongodb://127.0.0.1:27017/test_db' Connection.options = {     bufferMaxEntries:   0,     reconnectTries:     5000,     useNewUrlParser:    true,     useUnifiedTopology: true, }  module.exports = { Connection } 

Everywhere you require('./Connection'), the Connection.open() method will be available, as will the Connection.db property if it has been initialised.

const router = require('express').Router() const { Connection } = require('../lib/Connection.js')  // This should go in the app/server setup, and waited for. Connection.open()  router.get('/files', async (req, res) => {    try {      const files = await Connection.db.collection('files').find({})      res.json({ files })    }    catch (error) {      res.status(500).json({ error })    } })  module.exports = router