Event Booking System - Backend API

A robust, scalable backend service for an Event Booking platform. This architecture focuses on "immutable fundamentals"—specifically prioritizing strict resource management, concurrency control to prevent race conditions during ticket booking, and decoupled event-driven background processing.

🚀 Tech Stack

• Runtime & Framework: Node.js, Express.js
• Database & ORM: PostgreSQL (Dockerized), Prisma ORM (v7 Adapter Pattern)
• Architecture: Domain-driven feature modules, Event-driven background tasks

✨ Core Features

• Role-Based Access Control (RBAC): Strictly namespaced routes isolating ORGANIZER and CUSTOMER logic using custom header-based mock authentication.
• Concurrency Control (Atomic Transactions): Leverages Prisma $transaction and atomic decrements at the database level to guarantee ticket integrity and prevent double-booking under heavy load.
• Event-Driven Background Jobs: Utilizes Node's native EventEmitter to detach heavy async processing from the main HTTP thread.
  • Task 1: Booking Confirmation (Simulated Email)
  • Task 2: Event Update Notifications (Simulated broadcast to attendees)
• Dockerized Infrastructure: Containerized PostgreSQL database for isolated, reproducible local development.

---

🛠️ Getting Started

Prerequisites

• Node.js (v18+)
• Docker Desktop (Running)
• Windows PowerShell

1. Environment Setup

Create a .env file in the root directory:

DATABASE_URL="postgresql://postgres:password123@localhost:5433/event_booking?schema=public"
PORT=3000

2. Infrastructure & Database Initialization

Open your PowerShell terminal and run the following commands to spin up the database and apply the schema:

# Start the Dockerized PostgreSQL database
docker-compose up -d

# Install dependencies
npm install

# Push the schema and generate the Prisma Client
npx prisma db push
npx prisma generate

---

🧪 How to Run and Test the Application

To properly observe the background jobs and atomic transactions, follow this split-terminal testing flow.

Step 1: Start the Server (Terminal 1)

In your primary PowerShell window, boot up the development server:

npm run dev

Leave this terminal open and visible so you can watch the console.log outputs trigger from the background jobs.

Step 2: Seed the Database (Terminal 2)

Because the database enforces strict Foreign Key constraints, we need to create dummy users before we can book events. Open a second PowerShell window in the project root and run this seeding script:

node -r dotenv/config -e "const p = require('./src/config/db'); async function seed(){ await p.user.create({data:{id:'org-1', role:'ORGANIZER'}}); await p.user.create({data:{id:'cust-1', role:'CUSTOMER'}}); console.log('Users seeded!'); } seed();"

Step 3: Execute the API Flow (Postman / ThunderClient)

Use an API client to simulate the user journey. Important: We are using mock authentication. You must include the x-user-id and x-user-role headers in every request.

Action A: Create an Event (As Organizer)

• POST http://localhost:3000/api/organizer/events
• Headers:
  • x-user-id: org-1
  • x-user-role: ORGANIZER
• Body:

  {
    "title": "System Design Masterclass",
    "description": "Deep dive into scalable backend architectures.",
    "date": "2026-06-15T10:00:00Z",
    "totalTickets": 50
  }

(Copy the generated id from the response for the next steps).

Action B: Book a Ticket (As Customer)

• POST http://localhost:3000/api/customer/bookings
• Headers:
  • x-user-id: cust-1
  • x-user-role: CUSTOMER
• Body:

  {
    "eventId": "<PASTE_EVENT_ID_HERE>",
    "ticketsCount": 2
  }

👉 Check Terminal 1: You will immediately see the background job log: [BACKGROUND JOB] 📧 Email Action: Sending booking confirmation...

Action C: Update the Event (As Organizer)

• PUT http://localhost:3000/api/organizer/events/<PASTE_EVENT_ID_HERE>
• Headers:
  • x-user-id: org-1
  • x-user-role: ORGANIZER
• Body:

  {
    "title": "System Design Masterclass (Rescheduled!)"
  }

👉 Check Terminal 1: You will see the notification engine iterate through the attendees: [BACKGROUND JOB] 🔔 Notification: Alerting Customer cust-1 about updates...