Book Rental API (Express & MongoDB)

This is a simple backend service that:

• Fetches books containing the word “green” in their title from the Open Library API every 5 minutes
• Stores the books in a MongoDB database while preventing duplicates.
• Provides API endpoints to rent and return books.
• Ensures concurrency control so multiple users cannot rent the same book simultaneously.

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Tech Stack

• Backend: Node.js, Express.js
• Database: MongoDB with Mongoose ORM
• Scheduling: node-cron
• External API: Open Library API
• Testing: Jest, Supertest

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Setup & Installation

1. Clone the Repository

git clone https://github.com/yourusername/book-rental-api.git
cd book-rental-api

2. Install Dependencies

npm install

3. Configure Environment Variables

Create a .env file and add:

MONGO_URI=your_mongodb_connection_string
PORT=5000

4. Start the Server

For Development (with auto-reload using nodemon)

npm run dev

For Production

npm start

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API Endpoints

POSTMAN DOCUMENTATION

https://documenter.getpostman.com/view/29626287/2sAYkKJxjC

1. Get All Stored Books

GET /books

Returns the list of books stored in the database.

Response Example:

[
  {
    "_id": "65b6f0cf8c6a1b001e8b8a4a",
    "title": "Green Eggs and Ham",
    "author": "Dr. Seuss",
    "openLibraryId": "OL12345M",
    "isRented": false
  }
]

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2. Rent a Book

POST /books/rent

Rents a book if it’s not already rented.

Request Body:

{
  "bookId": "65b6f0cf8c6a1b001e8b8a4a",
  "userId": "user123"
}

Response (Success):

{
  "message": "Book rented successfully",
  "book": {
    "_id": "65b6f0cf8c6a1b001e8b8a4a",
    "title": "Green Eggs and Ham",
    "isRented": true,
    "rentedBy": "user123"
  }
}

Response (Already Rented):

{
  "error": "Book is already rented by another user"
}

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3. Return a Book

POST /books/return

Returns a book if it was previously rented by the user.

Request Body:

{
  "bookId": "65b6f0cf8c6a1b001e8b8a4a",
  "userId": "user123"
}

Response (Success):

{
  "message": "Book returned successfully",
  "book": {
    "_id": "65b6f0cf8c6a1b001e8b8a4a",
    "title": "Green Eggs and Ham",
    "isRented": false
  }
}

Response (Not Rented by User):

{
  "error": "Book was not rented by this user"
}

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Scheduled Job (Fetching Books from Open Library)

• A cron job runs every 5 minutes (or 10 seconds in test mode) to fetch books containing "green" in the title.
• The fetched books are upserted into MongoDB to avoid duplicates.

Modify Fetch Interval (For Testing)

To change the interval to 10 seconds, modify scheduler.js:

cron.schedule('*/10 * * * * *', async () => {
    console.log('Fetching books from Open Library...');
    await fetchAndStoreBooks();
});

For production, revert it to every 5 minutes:

cron.schedule('*/5 * * * *', async () => {
    console.log('Fetching books from Open Library...');
    await fetchAndStoreBooks();
});

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Project Structure

/book-rental-api
│── /models
│   ├── Book.js         # Mongoose model for books
│── /routes
│   ├── bookRoutes.js   # API routes for book rental system
│── /services
│   ├── bookService.js  # Service for fetching books from Open Library
│── /utils
│   ├── scheduler.js    # Cron job for fetching books every 5 min
│── server.js           # Main entry point
│── package.json        # Dependencies and scripts
│── README.md           # API Documentation

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Next Steps (Future Enhancements)

• User Authentication: Implement JWT-based authentication.
• Book Reviews API: Allow users to add ratings/reviews for books.
• Pagination & Filtering: Enhance /books endpoint to support pagination.

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