Express.js Student Management API

A RESTful API built with Express.js and MongoDB for managing student records. This project demonstrates fundamental Express.js concepts including routing, middleware, database integration, and CRUD operations.

📋 Table of Contents

• About Express.js
• Features
• Project Structure
• Prerequisites
• Installation
• Configuration
• Running the Application
• API Endpoints
• Express.js Core Concepts
• Middleware Explained
• Routing in Express
• Error Handling
• Testing with Postman/cURL
• Common Issues & Solutions

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🚀 About Express.js

Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. It simplifies the process of building server-side applications and APIs.

Why Express.js?

• Minimalist & Unopinionated: Provides the essentials without enforcing structure
• Robust Routing: Advanced routing with support for parameters, query strings, and middleware
• Middleware Support: Extensive middleware ecosystem for various functionalities
• HTTP Utilities: Simplified HTTP request/response handling
• Performance: Lightweight and fast
• Community: Large ecosystem with numerous plugins and extensions

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✨ Features

• ✅ RESTful API architecture
• ✅ MongoDB database integration with Mongoose ODM
• ✅ CRUD operations (Create, Read, Update, Delete)
• ✅ Environment variable configuration
• ✅ JSON request/response handling
• ✅ Error handling middleware
• ✅ Modular route organization
• ✅ Auto-restart with Nodemon

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📁 Project Structure

Week 2/
│
├── config/
│   └── db.js                 # Database connection configuration
│
├── models/
│   └── Student.js            # Mongoose schema and model for Student
│
├── routes/
│   └── studentRoutes.js      # Student-related API routes
│
├── .env                      # Environment variables (not in repo)
├── .gitignore                # Git ignore file
├── package.json              # Project dependencies and scripts
├── server.js                 # Main application entry point
└── README.md                 # Project documentation

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📦 Prerequisites

Before running this project, ensure you have the following installed:

• Node.js (v14 or higher) - Download
• npm (comes with Node.js) or yarn
• MongoDB (local installation or MongoDB Atlas account) - Download
• Postman (optional, for API testing) - Download

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⚙️ Installation

1. Clone the repository (or navigate to the project directory):

   https://github.com/PLP-MERN-Stack-Development/Week2-express-JS.git

2. Install dependencies:

   npm install

   This will install:

   • express - Web framework
   • mongoose - MongoDB ODM
   • dotenv - Environment variable management
   • nodemon - Development server with auto-restart

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🔧 Configuration

1. Create a .env file in the root directory:

   touch .env

2. Add the following environment variables:

   PORT=5000
   MONGO_URI=mongodb://localhost:27017/studentDB

   For MongoDB Atlas (cloud database):

   PORT=5000
   MONGO_URI=mongodb+srv://<username>:<password>@cluster0.xxxxx.mongodb.net/studentDB?retryWrites=true&w=majority

   Replace <username> and <password> with your MongoDB Atlas credentials.

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🏃 Running the Application

Development Mode (with auto-restart):

npm start

Production Mode:

npm run dev

The server will start at: http://localhost:5000

You should see:

Server running on http://localhost:5000
MongoDB Connected.....

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🛣️ API Endpoints

Base URL: http://localhost:5000

Method	Endpoint	Description	Request Body
GET	/	Welcome message	-
GET	/students	Get all students	-
POST	/students	Create a new student	{ "name": "John Doe", "age": 20, "email": "john@example.com" }
PUT	/students/:id	Update student by ID	{ "name": "Jane Doe", "age": 21, "email": "jane@example.com" }
DELETE	/students/:id	Delete student by ID	-

Example Requests:

1. Get All Students

curl -X GET http://localhost:5000/students

2. Create a Student

curl -X POST http://localhost:5000/students \
  -H "Content-Type: application/json" \
  -d '{"name":"Alice Smith","age":22,"email":"alice@example.com"}'

3. Update a Student

curl -X PUT http://localhost:5000/students/6501234567890abcdef12345 \
  -H "Content-Type: application/json" \
  -d '{"name":"Alice Johnson","age":23}'

4. Delete a Student

curl -X DELETE http://localhost:5000/students/6501234567890abcdef12345

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🧠 Express.js Core Concepts

1. Application Instance

The Express application is created using:

const express = require('express');
const app = express();

The app object represents your Express application and provides methods for:

• Routing HTTP requests
• Configuring middleware
• Rendering HTML views
• Registering template engines

2. Request (req) Object

Represents the HTTP request and contains properties for:

• req.body - Request body (requires express.json() middleware)
• req.params - Route parameters (e.g., /students/:id)
• req.query - Query string parameters (e.g., ?name=John&age=20)
• req.headers - Request headers
• req.method - HTTP method (GET, POST, etc.)

3. Response (res) Object

Represents the HTTP response that Express sends back:

• res.json() - Send JSON response
• res.send() - Send various types of responses
• res.status() - Set HTTP status code
• res.redirect() - Redirect to another route

4. Routing

Express provides methods for each HTTP verb:

app.get('/', (req, res) => { /* ... */ });     // GET request
app.post('/', (req, res) => { /* ... */ });    // POST request
app.put('/', (req, res) => { /* ... */ });     // PUT request
app.delete('/', (req, res) => { /* ... */ });  // DELETE request

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🔌 Middleware Explained

Middleware functions are functions that have access to the request (req), response (res), and the next middleware function in the application's request-response cycle.

Types of Middleware:

1. Application-Level Middleware

Applied to all routes:

app.use(express.json()); // Parses incoming JSON requests

2. Router-Level Middleware

Applied to specific router instances:

app.use("/students", require("./routes/studentRoutes"));

3. Built-in Middleware

• express.json() - Parses JSON payloads
• express.urlencoded() - Parses URL-encoded payloads
• express.static() - Serves static files

4. Third-Party Middleware

• dotenv - Loads environment variables
• cors - Enables Cross-Origin Resource Sharing
• morgan - HTTP request logger

5. Error-Handling Middleware

Special middleware with 4 parameters:

app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).json({ message: 'Something went wrong!' });
});

Middleware Flow:

Request → Middleware 1 → Middleware 2 → Route Handler → Response

Each middleware can:

• Execute code
• Modify request/response objects
• End the request-response cycle
• Call the next middleware using next()

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🛤️ Routing in Express

Basic Route Structure:

app.METHOD(PATH, HANDLER)

• METHOD: HTTP method (get, post, put, delete)
• PATH: URL path
• HANDLER: Callback function to execute

Route Parameters:

// URL: /students/123
router.get("/:id", (req, res) => {
    const studentId = req.params.id; // "123"
    // ... fetch student by ID
});

Query Strings:

// URL: /students?age=20&name=John
router.get("/", (req, res) => {
    const age = req.query.age;     // "20"
    const name = req.query.name;   // "John"
    // ... filter students
});

Router Modules:

Organize routes in separate files:

// studentRoutes.js
const router = express.Router();
router.get("/", getAllStudents);
router.post("/", createStudent);
module.exports = router;

// server.js
app.use("/students", studentRoutes);

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⚠️ Error Handling

Try-Catch Blocks:

All async operations use try-catch for error handling:

router.get("/", async (req, res) => {
    try {
        const students = await Student.find();
        res.json(students);
    } catch (error) {
        res.status(500).json({ message: error.message });
    }
});

Common HTTP Status Codes:

• 200: OK - Successful request
• 201: Created - Resource created successfully
• 400: Bad Request - Invalid request data
• 404: Not Found - Resource not found
• 500: Internal Server Error - Server error

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🧪 Testing with Postman/cURL

Using Postman:

1. GET Request:

   • Method: GET
   • URL: http://localhost:5000/students
   • Click "Send"

2. POST Request:

   • Method: POST
   • URL: http://localhost:5000/students
   • Headers: Content-Type: application/json
   • Body (raw JSON):

     {
       "name": "John Doe",
       "age": 20,
       "email": "john@example.com"
     }

3. PUT Request:

   • Method: PUT
   • URL: http://localhost:5000/students/6501234567890abcdef12345
   • Headers: Content-Type: application/json
   • Body: Updated fields

4. DELETE Request:

   • Method: DELETE
   • URL: http://localhost:5000/students/6501234567890abcdef12345

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🐛 Common Issues & Solutions

1. MongoDB Connection Failed

Error: MongooseServerSelectionError: connect ECONNREFUSED

Solutions:

• Ensure MongoDB is running locally: sudo systemctl start mongodb
• Check MONGO_URI in .env file
• For Atlas, verify network access settings (allow your IP)

2. Port Already in Use

Error: EADDRINUSE: address already in use :::5000

Solutions:

• Change port in .env file
• Kill process using port: lsof -ti:5000 | xargs kill -9

3. Cannot POST/GET Data

Possible Causes:

• Missing express.json() middleware
• Incorrect Content-Type header
• Route not properly defined

Solution:

app.use(express.json()); // Add this before routes

4. Module Not Found

Error: Cannot find module 'express'

Solution:

npm install

5. Environment Variables Not Loading

Solution:

• Ensure .env file is in root directory
• Add require('dotenv').config() at top of server.js
• Restart server after changes

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📚 Additional Resources

Official Documentation:

• Express.js Official Docs
• Mongoose Documentation
• Node.js Documentation

Tutorials:

• Express.js Guide
• REST API Best Practices
• MongoDB University

Tools:

• Postman - API testing
• MongoDB Compass - Database GUI
• Nodemon - Auto-restart server

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🤝 Contributing

Feel free to fork this project, submit issues, or create pull requests for improvements!

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📝 License

This project is open-source and available under the ISC License.

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👨‍💻 Author

Created as part of the PLP MERN Stack July Cohort - Week 2 learning materials.

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Happy Coding! 🚀