Connecting Express to MongoDB with Mongoose, .env, and .gitignore

As you build more powerful Express apps, connecting to a database becomes essential. In this blog, we’ll walk through how to:

Connect an Express app to MongoDB using Mongoose
Secure your credentials using .env
Prevent sensitive files from being tracked with .gitignore

Let’s get started.

Step 1: Install Required Packages

In your project directory, install:

npm install mongoose dotenv

mongoose: ODM (Object Data Modeling) library for MongoDB
dotenv: Loads environment variables from .env files

Step 2: Create `.env` File

In the root of your project, create a .env file:

touch .env

Add your MongoDB connection string:

MONGO_URI=mongodb+srv://<username>:<password>@cluster.mongodb.net/myDatabase
PORT=5000

Never share this file publicly.

Step 3: Setup `.gitignore`

To ensure .env and other sensitive files aren’t committed to Git, create a .gitignore file:

touch .gitignore

Add this to .gitignore:

node_modules/
.env

Now Git will ignore node_modules (which can be reinstalled) and .env (which is sensitive).

Step 4: Create MongoDB Config

Create a file at src/config/db.js:

const mongoose = require('mongoose');

const connectDB = async () => {
  try {
    await mongoose.connect(process.env.MONGO_URI);
    console.log('MongoDB connected successfully');
  } catch (error) {
    console.error('MongoDB connection failed:', error.message);
    process.exit(1);
  }
};

module.exports = connectDB;

Step 5: Use `dotenv` and Connect DB

Update your server.js or app.js:

// server.js
const dotenv = require('dotenv');
dotenv.config(); // Load .env before anything else

const express = require('express');
const connectDB = require('./src/config/db');

const app = express();

// Connect to MongoDB
connectDB();

// Middleware
app.use(express.json());

// Routes
app.get('/', (req, res) => {
  res.send('Server running with MongoDB');
});

const PORT = process.env.PORT || 5000;
app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`);
});

Final Folder Snapshot

my-express-app/
├── node_modules/
├── src/
│   └── config/
│       └── db.js
├── .env
├── .gitignore
├── package.json
└── server.js

Step 6: Run Your App

Start the server:

node server.js

If successful, you’ll see:

MongoDB connected successfully
Server is running on http://localhost:5000

Bonus Tip: Use Environment Variables in Production

When you deploy (e.g., to Render or Vercel), add your MONGO_URI and PORT values to their dashboard under Environment Variables — no need to upload .env.