How to load mongodb URI from .env file on heroku? - node.js

Question

I am a beginner to MERN stack and I deployed my nodejs app to heroku but the app is unable to connect to mongodb atlas and data from the database does not load when I give the mongodb uri via an environment variable.It works fine when I directly give the uri via a variable.Also when run locally,the app connects to atlas without any problem using environment variable.Any idea why its not working on heroku and how to fix it?
server.js
const express = require('express'); //nodejs framework for creating web apps
const cors = require('cors');
const mongoose = require('mongoose');
const path = require('path');
require('dotenv').config(); //for setting environment variables on server
const app = express(); //creating the app
//Serve static assets if in production
if(process.env.NODE_ENV ==='production'){
//Set static folder
app.use(express.static('client/build'));
app.get('*',(req, res) => {
res.sendFile(path.resolve(__dirname,'client','build','index.html'));
});
}
////////////////////////////////////////
const port = process.env.PORT || 5000;
app.use(cors()); //for cross origin resource sharing ie.cross domain requests
app.use(express.json()); //for handling json data
const uri = process.env.ATLAS_URI;
//its works fine when I give it as below
//const uri="mongodb+srv://jose:<password>#exercisecluster-rmqkg.gcp.mongodb.net/test?retryWrites=true&w=majority"
mongoose.connect(uri,{ useNewUrlParser: true, useCreateIndex: true ,useUnifiedTopology: true });
const connection = mongoose.connection;
connection.once('open',() => {
console.log('Database connection established successfully');
})
const exercisesRouter = require('./routes/exercises');
const usersRouter = require('./routes/users');
//executes the files in the second argument when user enters the url 'rooturl/firstargument'
app.use('/exercises',exercisesRouter);
app.use('/users',usersRouter);
app.listen(port,() => {
console.log(`Server is running on port:${port}`);
});

Answer 1

In your heroku project you need to setup an env variable ATLAS_URI and enter the value for your mongodb uri.
To do so go to the settings tab in your heroku app, then click on reveal config vars, and then enter the key and value for your mongo uri.
Hope this helps