Interview Test API Project

A simple hotel booking API designed for developer interviews. This project demonstrates clean architecture patterns, Domain-Driven Design (DDD) principles, and includes deliberate issues for discussion during technical interviews.

🎯 Project Overview

This API manages guests and their hotel bookings with the following features:

• Guest management (CRUD operations)
• Booking management with business logic
• Entity Framework Core with In-Memory database
• RESTful API with Swagger documentation
• Unit tests with xUnit

Domain Entities

• Guest: Represents hotel guests with personal information and address
• Booking: Represents room bookings with dates, rates, and status
• Address: Value object for guest addresses

🚀 Quick Start

Prerequisites

• .NET 8.0 SDK
• Git

Clone and Run

git clone <repository-url>
cd InterviewTest
dotnet build
dotnet run --project src/InterviewTest.Api

The API will start on http://localhost:5124 with Swagger UI available at the root URL.

Running Tests

dotnet test

📋 API Endpoints

Guests

• GET /api/guests - Get all guests
• GET /api/guests/{id} - Get guest by ID
• GET /api/guests/with-bookings - Get guests with their bookings (⚠️ Performance Issue)
• GET /api/guests/search?term={searchTerm} - Search guests
• POST /api/guests - Create new guest (🐛 Validation Bug)
• PUT /api/guests/{id} - Update guest
• DELETE /api/guests/{id} - Delete guest
• GET /api/guests/{id}/bookings - Get guest's bookings

Bookings

• GET /api/bookings - Get all bookings
• GET /api/bookings/{id} - Get booking by ID
• GET /api/bookings/active - Get active bookings
• POST /api/bookings - Create new booking (🐛 Validation Bug)
• PUT /api/bookings/{id} - Update booking
• DELETE /api/bookings/{id} - Delete booking

🐛 Built-in Issues for Interview Discussion

1. Performance Issue (N+1 Query Problem)

Location: GuestRepository.GetGuestsWithBookingsAsync() and BookingService.CalculateBookingRevenueForGuestAsync()

Problem: The GET /api/guests/with-bookings endpoint causes N+1 queries.

Test:

curl http://localhost:5124/api/guests/with-bookings

Discussion Points:

• How to identify N+1 problems
• Entity Framework's Include() method
• Query optimization strategies

2. Validation Bug

Location: GuestsController.CreateGuest() and BookingService.CreateBookingAsync()

Problem: Date validation logic is incorrect - uses >= instead of > for date of birth validation.

Test:

curl -X POST http://localhost:5124/api/guests \
  -H "Content-Type: application/json" \
  -d '{
    "firstName": "Test",
    "lastName": "User", 
    "email": "test@example.com",
    "dateOfBirth": "2024-07-29T00:00:00",
    "address": {"street": "123 St", "city": "City", "state": "ST", "postalCode": "12345", "country": "USA"}
  }'

Discussion Points:

• Debugging validation logic
• Understanding business requirements
• Testing edge cases

3. Code Smell - Violation of DDD Principles

Location: BookingService.cs

Problems:

• Service mixes domain logic with data access concerns
• Direct console logging in domain service
• Validation logic should be separated

Discussion Points:

• Domain-Driven Design principles
• Separation of concerns
• Service layer responsibilities
• Where to place validation logic

4. Unit Test Gap - Failing Test

Location: BookingTests.CalculateTotal_ShouldIncludeTax()

Problem: The Booking.CalculateTotal() method doesn't include tax in the calculation.

Run Test:

dotnet test --filter "CalculateTotal_ShouldIncludeTax"

Discussion Points:

• Test-driven development
• Business logic testing
• Debugging failing tests

🎯 Interview Tasks

Task 1: Fix the Validation Bug (15 minutes)

1. Clone and run the project
2. Test the guest creation endpoint with today's date
3. Identify and fix the validation logic error
4. Verify the fix works

Task 2: Identify and Explain the Code Smell (10 minutes)

1. Review the BookingService class
2. Identify violations of DDD principles
3. Explain how you would refactor it
4. Discuss the benefits of the refactoring

Task 3: Fix the Failing Unit Test (10 minutes)

1. Run the tests and identify the failing test
2. Debug the CalculateTotal() method
3. Fix the business logic bug
4. Verify all tests pass

Task 4: Optimize the Performance Issue (15 minutes)

1. Test the /api/guests/with-bookings endpoint
2. Identify the N+1 query problem
3. Fix the repository method to use eager loading
4. Explain other optimization strategies

Task 5: Add New Endpoint (Extension - if time permits)

Add a GET /api/guests/{id}/bookings/active endpoint that returns only active bookings for a specific guest.

💡 Interview Questions

Setup & Debugging

• How would you approach running this project for the first time?
• What would you do if the API didn't start properly?
• How do you identify performance issues in APIs?

Domain & Code Quality

• What DDD principles are violated in this codebase?
• How would you improve the separation of concerns?
• What would you refactor first and why?

Entity Framework & Database

• How would you optimize the database queries?
• What EF Core features would you use for better performance?
• How would you handle database migrations in production?

Testing & Quality

• What testing strategies would you implement?
• How would you improve the current test coverage?
• What tools would you use for API testing?

🛠️ Architecture

InterviewTest/
├── src/
│   ├── InterviewTest.Api/         # Web API layer
│   ├── InterviewTest.Core/        # Domain layer (entities, services, interfaces)
│   └── InterviewTest.Infrastructure/ # Data access layer
└── tests/
    ├── InterviewTest.Api.Tests/   # API integration tests
    └── InterviewTest.Core.Tests/  # Unit tests

Key Patterns Used

• Clean Architecture
• Repository Pattern
• Domain-Driven Design
• Dependency Injection
• RESTful API design

📚 Learning Resources

• Clean Architecture
• Domain-Driven Design
• Entity Framework Core Documentation
• ASP.NET Core Web API

🔧 Troubleshooting

Common Issues

Build Failures

• Ensure .NET 8.0 SDK is installed
• Run dotnet restore to restore packages

Port Already in Use

• The API runs on port 5124 (HTTP) and 7126 (HTTPS)
• Change ports in launchSettings.json if needed

Database Issues

• Project uses In-Memory database - no setup required
• Data is seeded automatically on startup

📝 Notes for Interviewers

• Allow 5-10 minutes for initial setup and exploration
• Focus on problem-solving approach rather than perfect solutions
• Encourage candidates to explain their thought process
• Use the built-in issues as conversation starters
• Observe coding style and testing practices

Expected completion time: 45-60 minutes for all tasks.