ASP.NET Core Web API with 3-Tier Architecture and Iterator Pattern

// Sardar Mudassar Ali Khan
// Models/LibraryBook.cs
public class LibraryBook
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Author { get; set; }
}

// DataAccessLayer/LibraryBookRepository.cs
using System.Collections;
using System.Collections.Generic;

public interface ILibraryBookIterator
{
    LibraryBook Next();
    bool HasNext();
}

public interface ILibraryBookRepository : IEnumerable<LibraryBook>
{
    void Add(LibraryBook book);
    void Update(LibraryBook book);
    void Delete(int id);
    LibraryBook GetById(int id);
    ILibraryBookIterator CreateIterator();
}

public class LibraryBookRepositoryIterator: ILibraryBookIterator
{
    private readonly List<LibraryBook> books;
    private int position = 0;

    public LibraryBookRepositoryIterator(List<LibraryBook> books)
    {
        this.books = books;
    }

    public LibraryBook Next()
    {
        var book = books[position];
        position++;
        return book;
    }

    public bool HasNext()
    {
        return position < books.Count;
    }
}

public class LibraryBookRepository: ILibraryBookRepository
{
    private List<LibraryBook> books;

    public LibraryBookRepository()
    {
        books = new List<LibraryBook>();
    }

    public void Add(LibraryBook book)
    {
        books.Add(book);
    }

    public void Update(LibraryBook book)
    {
        var existingBook = GetById(book.Id);
        if (existingBook != null)
        {
            // Update properties
            existingBook.Title = book.Title;
            existingBook.Author = book.Author;
            // Update other properties as needed
        }
    }

    public void Delete(int id)
    {
        var bookToRemove = GetById(id);
        if (bookToRemove != null)
        {
            books.Remove(bookToRemove);
        }
    }

    public LibraryBook GetById(int id)
    {
        return books.FirstOrDefault(b => b.Id == id);
    }

    public IEnumerator<LibraryBook> GetEnumerator()
    {
        return books.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    public ILibraryBookIterator CreateIterator()
    {
        return new LibraryBookRepositoryIterator(books);
    }
}

Step 3. Implement Business Logic Layer (BLL)

// Sardar Mudassar Ali Khan
// BusinessLogicLayer/LibraryBookService.cs
public class LibraryBookService
{
    private readonly ILibraryBookRepository book repository;

    public LibraryBookService(ILibraryBookRepository bookRepository)
    {
        this.bookRepository = bookRepository;
    }

    public void AddBook(LibraryBook book)
    {
        bookRepository.Add(book);
    }

    public void UpdateBook(LibraryBook book)
    {
        bookRepository.Update(book);
    }

    public void DeleteBook(int id)
    {
        bookRepository.Delete(id);
    }

    public LibraryBook GetBookById(int id)
    {
        return bookRepository.GetById(id);
    }

    public IEnumerable<LibraryBook> GetAllBooks()
    {
        return bookRepository;
    }
}

Step 4. Implement API Controllers (Presentation Layer)

// Sardar Mudassar Ali Khan
// Controllers/LibraryBookController.cs
[ApiController]
[Route("api/[controller]")]
public class LibraryBookController : ControllerBase
{
    private readonly LibraryBookService bookService;

    public LibraryBookController(LibraryBookService bookService)
    {
        this.bookService = bookService;
    }

    [HttpPost]
    public IActionResult AddBook([FromBody] LibraryBook book)
    {
        bookService.AddBook(book);
        return Ok();
    }

    [HttpPut]
    public IActionResult UpdateBook([FromBody] LibraryBook book)
    {
        bookService.UpdateBook(book);
        return Ok();
    }

    [HttpDelete("{id}")]
    public IActionResult DeleteBook(int id)
    {
        bookService.DeleteBook(id);
        return Ok();
    }

    [HttpGet("{id}")]
    public IActionResult GetBookById(int id)
    {
        var book = bookService.GetBookById(id);
        return Ok(book);
    }

    [HttpGet]
    public IActionResult GetAllBooks()
    {
        var books = bookService.GetAllBooks();
        return Ok(books);
    }
}

Step 5. Dependency Injection (Startup.cs)

// Sardar Mudassar Ali Khan
// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    // Other configurations

    services.AddSingleton<ILibraryBookRepository, LibraryBookRepository>();
    services.AddScoped<LibraryBookService>();
    services.AddControllers();
}

Conclusion

In conclusion, we've implemented a simple ASP.NET Core Web API with a 3-tier architecture (Data Access Layer, Business Logic Layer, and Presentation Layer) for managing a collection of library books. We incorporated the Iterator Design Pattern to encapsulate the iteration logic for the collection of LibraryBook objects.

Key steps in the implementation

1. Model Definition

• Defined the LibraryBook model to represent the data structure.

2. Data Access Layer (DAL)

• Created the ILibraryBookIterator and ILibraryBookRepository interfaces.
• Implemented the LibraryBookRepositoryIterator class for the iterator pattern.
• Updated the LibraryBookRepository class to include the iterator pattern using the CreateIterator method.

3. Business Logic Layer (BLL)

• Implemented the LibraryBookService class, which serves as an intermediary between the DAL and the API controllers.

4. API Controllers (Presentation Layer)

• Created the LibraryBookController class to handle HTTP requests and interact with the LibraryBookService

5. Dependency Injection (Startup. cs)

• Configured dependency injection for the ILibraryBookRepository and LibraryBookService in the Startup.cs file.

This implementation provides a foundation for a scalable and maintainable application, with a separation of concerns between different layers. The Iterator Design Pattern enhances the flexibility and extensibility of the code by encapsulating the iteration logic, allowing for easier changes in the future.