In this section, we will learn how to build a REST API using MongoDB as the database. We will use Node.js and Express.js to create the API endpoints and perform CRUD operations on MongoDB.

Before we start, make sure you have the following installed:

• Node.js
• npm (Node Package Manager)
• MongoDB

1. Create a new directory for your project:

   mkdir rest-api-mongodb
   cd rest-api-mongodb
   

2. Initialize a new Node.js project:

   npm init -y
   

3. Install the required dependencies:

   npm install express mongoose body-parser
   

1. Create a new file named server.js:

   const express = require('express');
   const mongoose = require('mongoose');
   const bodyParser = require('body-parser');
   
   const app = express();
   const port = 3000;
   
   // Middleware
   app.use(bodyParser.json());
   
   // MongoDB connection
   mongoose.connect('mongodb://localhost:27017/restapi', {
       useNewUrlParser: true,
       useUnifiedTopology: true
   });
   
   const db = mongoose.connection;
   db.on('error', console.error.bind(console, 'connection error:'));
   db.once('open', () => {
       console.log('Connected to MongoDB');
   });
   
   app.listen(port, () => {
       console.log(`Server is running on port ${port}`);
   });
   

2. Run the server:

   node server.js
   

   You should see the message "Connected to MongoDB" and "Server is running on port 3000".

1. Create a new directory named models and a file named User.js inside it:

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

1. Create a new directory named routes and a file named userRoutes.js inside it:

   const express = require('express');
   const router = express.Router();
   const User = require('../models/User');
   
   // Create a new user
   router.post('/users', async (req, res) => {
       const user = new User(req.body);
       try {
           await user.save();
           res.status(201).send(user);
       } catch (error) {
           res.status(400).send(error);
       }
   });
   
   // Read all users
   router.get('/users', async (req, res) => {
       try {
           const users = await User.find();
           res.status(200).send(users);
       } catch (error) {
           res.status(500).send(error);
       }
   });
   
   // Read a user by ID
   router.get('/users/:id', async (req, res) => {
       const _id = req.params.id;
       try {
           const user = await User.findById(_id);
           if (!user) {
               return res.status(404).send();
           }
           res.status(200).send(user);
       } catch (error) {
           res.status(500).send(error);
       }
   });
   
   // Update a user by ID
   router.patch('/users/:id', async (req, res) => {
       const _id = req.params.id;
       try {
           const user = await User.findByIdAndUpdate(_id, req.body, { new: true, runValidators: true });
           if (!user) {
               return res.status(404).send();
           }
           res.status(200).send(user);
       } catch (error) {
           res.status(400).send(error);
       }
   });
   
   // Delete a user by ID
   router.delete('/users/:id', async (req, res) => {
       const _id = req.params.id;
       try {
           const user = await User.findByIdAndDelete(_id);
           if (!user) {
               return res.status(404).send();
           }
           res.status(200).send(user);
       } catch (error) {
           res.status(500).send(error);
       }
   });
   
   module.exports = router;
   

2. Update server.js to use the user routes:

   const express = require('express');
   const mongoose = require('mongoose');
   const bodyParser = require('body-parser');
   const userRoutes = require('./routes/userRoutes');
   
   const app = express();
   const port = 3000;
   
   // Middleware
   app.use(bodyParser.json());
   
   // MongoDB connection
   mongoose.connect('mongodb://localhost:27017/restapi', {
       useNewUrlParser: true,
       useUnifiedTopology: true
   });
   
   const db = mongoose.connection;
   db.on('error', console.error.bind(console, 'connection error:'));
   db.once('open', () => {
       console.log('Connected to MongoDB');
   });
   
   // Use user routes
   app.use('/api', userRoutes);
   
   app.listen(port, () => {
       console.log(`Server is running on port ${port}`);
   });
   

You can use tools like Postman or curl to test the API endpoints.

In this section, we have learned how to build a REST API using MongoDB, Node.js, and Express.js. We covered setting up the project, connecting to MongoDB, defining a data model, creating CRUD endpoints, and testing the API. This knowledge can be extended to build more complex applications and integrate additional features as needed.