Assignemnt_Backend_3.md

The Library (due by CP 4)

Introduction

In this lab, you’ll build a small API for managing books using Node.js, Express, and Mongoose.

By the end of the exercise, you will:

• Understand how to define and validate Mongoose models
• Practice connecting to MongoDB
• Learn basic CRUD operations
• Handle errors gracefully
• Test your API using Postman

Requirements

1. Fork this repository

2. Clone it to your local machine

3. Run the following commands to set up your project:

   npm install
   npm start
   

Iteration 0 – Initial Setup

Inside your project folder:

• You’ll find an index.js file where you’ll configure Express and Mongoose.
• Create a folder /models to store your Mongoose models.
• Create a folder /routes to store your Express routes.

You’ll connect to MongoDB using Mongoose like this:

const mongoose = require("mongoose");
const MONGODB_URI = "mongodb://127.0.0.1:27017/book-library";

mongoose
  .connect(MONGODB_URI)
  .then(x => console.log(`Connected to MongoDB: ${x.connection.name}`))
  .catch(err => console.error("Error connecting to MongoDB", err));

Iteration 1 – Book Schema

Create a file /models/Book.model.js and define the following schema:

Field	Type	Validation / Notes
title	String	Required, unique
author	String	Required
genre	String	Enum: Fiction, Non-Fiction, Sci-Fi, Fantasy, Biography, Other
publishedYear	Number	Minimum value: 0
rating	Number	Default: 0, Minimum: 0, Maximum: 5
createdAt	Date	Default: today

Export the model:

module.exports = mongoose.model("Book", bookSchema);

Iteration 2 – Create Book Routes

Create a file /routes/book.routes.js and add the following routes:

Method	Route	Description
GET	/books	Get all books
GET	/books/:id	Get one book by ID
POST	/books	Create a new book
PUT	/books/:id	Update a book
DELETE	/books/:id	Delete a book

Remember to handle errors properly:

• Return 400 for validation errors
• Return 404 if the book isn’t found
• Return 500 for unexpected errors

Example error handler:

res.status(400).json({ error: error.message });

In index.js, import and use your routes:

const bookRoutes = require("./routes/book.routes");
app.use("/api", bookRoutes);

Iteration 3 – Test with Postman

1. Run your server:

   npm run dev
   

2. Open Postman and test all routes:

   • POST /api/books → create a new book
   • GET /api/books → list all books
   • GET /api/books/:id → get one
   • PUT /api/books/:id → edit a book
   • DELETE /api/books/:id → delete one

💡 Tip: Use the “Body → raw → JSON” tab to send JSON data when testing POST and PUT requests.

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Iteration 4: Close Database

After your operations, gracefully close the database connection:

mongoose.connection.close();

Use this when running short scripts (like seed files).

(Bonus) Iteration 4 – Error Handling Practice

Enhance your routes to handle these scenarios:

• If a required field is missing → respond with 400 and a helpful message.
• If the book ID format is invalid → catch the CastError from Mongoose and respond with 400.
• Wrap all database operations in try/catch.

Example:

try {
  const book = await Book.findById(req.params.id);
  if (!book) return res.status(404).json({ error: "Book not found" });
  res.json(book);
} catch (error) {
  if (error.name === "CastError") {
    res.status(400).json({ error: "Invalid ID format" });
  } else {
    res.status(500).json({ error: "Server error" });
  }
}

✅ Submission

When finished:

git add .
git commit -m "Completed MongoDB + Mongoose API lab"
git push origin master

Then, create a Pull Request so we can review your work.

❤️ Happy Coding!