📚 Library Management Backend

This project is a backend API for managing a library system. It supports book catalog management, inventory tracking, borrowing and returning books, and automatic customer reputation scoring.

Built using NestJS, Prisma ORM, and PostgreSQL.

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⚙️ Setup Instructions

1️⃣ Prerequisites

Make sure you have the following installed:

• Node.js (v18 or later)
• npm
• PostgreSQL
• Git

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2️⃣ Clone the Repository

git clone https://github.com/your-username/libmanage-backend.git cd libmanage-backend

3️⃣ Install Dependencies

npm install

4️⃣ Add Env Variables

DATABASE_URL="postgresql://USERNAME:PASSWORD@localhost:5432/libmanage?schema=public"

5️⃣ Prisma Setup

npx prisma generate npx prisma migrate dev

How to run Server:

npm run start:dev

🧠 Approach and Design Explanation

Modular Architecture

The application is divided into the following main modules:

• Catalog Module
  Responsible for managing book-related information such as titles, genres, language, ISBN, and authors. It handles searching, filtering, pagination, and soft deletion of books.

• Inventory Module
  Manages physical book copies, including their availability status (e.g., AVAILABLE, LOANED, DAMAGED). This module tracks multiple copies of the same book and supports soft deletion and status updates.

• Circulation Module
  Handles borrowing and returning of books. It coordinates updates across multiple resources (loans, book copies, and customers) using database transactions to ensure consistency.

• Reputation Module
  Calculates and applies customer reputation score changes automatically based on borrowing behavior. Scores are adjusted when a book is returned early, on time, or late, preventing manual manipulation from the client.

Data Integrity and Transactions

Prisma ORM is used to provide type-safe database access and transaction management. Critical operations such as borrowing and returning books are executed within transactions to guarantee data integrity.

Soft Deletes

Soft deletes are implemented using deletedAt fields. This approach preserves historical data while preventing permanently removed records from appearing in active queries.

API Design Principles

The system follows clean RESTful API principles:

• URLs identify resources (domain concepts)
• HTTP methods describe actions
• Controllers handle routing only
• Business logic is encapsulated within services

This design ensures the backend is maintainable, scalable, and aligned with real-world library workflows.