Connect MongoDB with NodeJS & Express

1 - Install the necessary dependencies:

You will need to install the mongodb and mongoose npm packages. You can install them using the following command:

$npm install mongodb mongoose

2 - Set up the database connection:

In your Express application, you will need to create a database connection using Mongoose. You can do this by creating a mongoose object and using its connect() method to connect to your database. Here's an example:

const mongoose = require('mongoose');
const uri = 'mongodb://localhost:27017/mydatabase';
mongoose.connect(uri, {
    useNewUrlParser: true,
    useUnifiedTopology: true
});
const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {
    console.log("Connected to database");
});

In the example above, we create a mongoose object and connect to a local MongoDB database called mydatabase. We also set up a listener for the open event, which indicates that the connection was successful.

3- Define a schema for your data:

Before you can start using MongoDB in your Express application, you need to define a schema for your data. This defines the structure of your data and the types of values that are allowed. You can do this using the mongoose.Schema() method. Here's an example:

const mongoose = require('mongoose');
const userSchema = new mongoose.Schema({
    name: String,
    email: String,
    age: Number
});
const User = mongoose.model('User', userSchema);
module.exports = User;

In the example above, we define a schema for a User object with a name, email, and age field. We also create a model from the schema using the mongoose.model() method, and export it so that it can be used in other parts of our application.

4 - Use the database in your Express routes:

Once you have set up your database connection and defined your data schema, you can use MongoDB in your Express routes. Here's an example:

const express = require('express');
const router = express.Router();
const User = require('../models/user');
router.get('/users', (req, res) => {
    User.find((err, users) => {
        if (err) {
            console.error(err);
            res.status(500).send("Error retrieving users from database");
        } else {
            res.json(users);
        }
    });
});
module.exports = router;

In the example above, we define a route that retrieves all users from the database using the User.find() method. If an error occurs, we send a 500 error response. Otherwise, we send a JSON response with the users.