Connecting Mongodb databse to node.js server

Question

I have been trying to make a web app using node.js and express and decided to work with mongodb. I am using mongodb node.js driver version: 4.3.1 I have tried all the possible ways to connect the node.js server with my mongodb atlas database.

const app = require('./app');

const MongoClient = require('mongodb').MongoClient

const Url = 'mongodb+srv://todoAppUser:<myOriginalPasswordHere>@cluster0.6lvjr.mongodb.net/myDatabase?retryWrites=true&w=majority';

MongoClient.connect(Url, function (err, client) {
  if (err) throw err;

  var db = client.db('myDatabase');

  db.collection('products').findOne({}, function (findErr, result) {
    if (findErr) throw findErr;
    console.log(result.name);
    client.close();
  });
});

Answer 1

This can't work, because modules are evaluated synchronously. Your callback is called asynchronously but your module has been alread evaluated at this time. Means module.exports has no effect and require('./db').collection() is not defined. Please see Node.js Modules for details.

To solve your problem, handle the connection stored in a module internal variable and export a getter instead of the connection variable itself.

// db.js
let client;
let db;

function connectDB(url, dbName) {
    client = new MongoClient(url);

    return new Promise(function(resolve, reject) {
        client.connect(function(err) {
            if(err) return reject(err);

            db = client.db(dbName);
            return resolve(db);
        });
    });
}

function getCurrentDB() {
    return db;
}

module.exports.connectDB = connectDB;
module.exports.getCurrentDB = getCurrentDB;

Then reuse your opened connection in other files like the following:

// other.js
const db = require("./db.js");

db.getCurrentDB().collection("product");

Of course, getCurrentDB() can only return a database connection if a connection has been established via connectDB() beforehand. So you have to wait for the resolution of the Promise .