Check if mongoDB is connected

Question

I have mongoDB in my app.

I want to check if mongoDB is connected, before I listen to the app.

Is it the best way for doing it?

This is my server.js file:

var express = require('express');
var mongoDb = require('./mongoDb');
var app = express();

init();

function init() {
    if (mongoDb.isConnected()) {
      app.listen(8080, '127.0.0.1');
    }
    else {
      console.log('error');
    }
}

isConnected runs getDbObject. getDbObject connects to mongoDB and returns an object: connected (true/false), db (dbObject or error).

Then, isConnected resolve/reject by connected property.

This is mongoDb.js file:

//lets require/import the mongodb native drivers.
var mongodb = require('mongodb');
// Connection URL. This is where your mongodb server is running.
var url = 'mongodb://localhost:27017/myDb';

var connectingDb; // promise

//We need to work with "MongoClient" interface in order to connect to a mongodb server.
var MongoClient = mongodb.MongoClient;

init();

module.exports = {
    isConnected: isConnected
}

// Use connect method to connect to the Server
function init() {
  connectingDb = new Promise(
    function (resolve, reject) {
      MongoClient.connect(url, function (err, db) {
        if (err) {
          console.log('Unable to connect to the mongoDB server. Error:', err);
          reject(err);
        }
        else {
          console.log('Connection established to', url);

          //Close connection
          //db.close();
          resolve(db);
        }
      });

    }
  );
}

function getDbObject() {
  return connectingDb().then(myDb => {
                                       return {
                                          connected: true,
                                          db: myDb
                                        }
                                      }
                              )
                       .catch(err =>  {
                                        return {
                                          connected: false,
                                          db: err
                                        }
                                      }
                             )
}

function isConnected() {
    return new Promise(
        function(resolve, reject) {
          var obj = getDbObject();
          if (obj.connected == true) {
            console.log('success');
            resolve(true);
          }
          else {
            console.log('error');
            reject(false);
          }
        }
    )

}

Any help appreciated!

Answer 1

there are multiple ways depends on how your DB is configured. for a standalone (single) instance. You can use something like this

Db.connect(configuration.url(), function(err, db) {
  assert.equal(null, err);

if you have a shared environment with config servers and multiple shards you can use

db.serverConfig.isConnected()

Answer 2

Let client be the object returned from MongoClient.connect:

let MongoClient = require('mongodb').MongoClient
let client = await MongoClient.connect(url ...
...

This is how i check my connection status:

function isConnected() {
  return !!client && !!client.topology && client.topology.isConnected()
}

This works for version 3.1.1 of the driver. Found it here.