Architectural Patterns in .NET

Model-View-Controller (MVC)

The MVC pattern separates an application into three interconnected parts: the Model, the View, and the Controller. This promotes a clear separation of concerns, making it easier to manage complex applications.

Model: Represents the data and the business logic of the application.

View: Responsible for presenting the data to the user and handling user input. It's typically a UI element.

Controller: Acts as an intermediary between the Model and the View. It handles user requests, manipulates the Model, and selects the appropriate View to display.

// Example snippet of a Controller in ASP.NET Core MVC
public class HomeController : Controller
{
    private readonly IProductService _productService;

    public HomeController(IProductService productService)
    {
        _productService = productService;
    }

    public IActionResult Index()
    {
        var products = _productService.GetAllProducts();
        return View(products);
    }
}

Model-View-ViewModel (MVVM)

MVVM is a UI design pattern commonly used in frameworks that support data binding, such as WPF, UWP, Xamarin.Forms, and Blazor. It's an evolution of MVC, specifically tailored for UI development.

Model: Same as in MVC, represents the application's data and business logic.

View: The UI element itself (e.g., XAML, HTML). It's declarative and typically has no code-behind logic.

ViewModel: An abstraction of the View. It exposes data from the Model in a format that the View can easily consume and includes commands that the View can bind to. It handles the presentation logic.

// Example concept of a ViewModel in C# for data binding
public class ProductListViewModel : ObservableObject // Assuming ObservableObject for INotifyPropertyChanged
{
    private readonly IProductService _productService;

    public ObservableCollection<Product> Products { get; } = new();

    public ProductListViewModel(IProductService productService)
    {
        _productService = productService;
        LoadProducts();
    }

    private void LoadProducts()
    {
        var products = _productService.GetAllProducts();
        foreach (var product in products)
        {
            Products.Add(product);
        }
    }
}

Repository Pattern

The Repository pattern provides an abstraction layer between the data access logic and the rest of the application. It treats a collection of domain objects as if it were an in-memory collection, abstracting away the underlying data storage mechanism.

Benefits: Decouples application from data source, makes testing easier, promotes code reusability.

// Example interface for a Product Repository
public interface IProductRepository
{
    Task<Product> GetByIdAsync(int id);
    Task<IEnumerable<Product>> GetAllAsync();
    Task AddAsync(Product product);
    Task UpdateAsync(Product product);
    Task DeleteAsync(int id);
}

Dependency Injection (DI)

Dependency Injection is a design pattern where an object receives other objects that it depends on (its dependencies) from an external source rather than creating them itself. .NET has first-class support for DI, making it a fundamental pattern for building maintainable applications.

Benefits: Improved testability, looser coupling, better modularity.

// Example of registering a service in ASP.NET Core
// In Startup.cs or Program.cs
services.AddScoped<IProductRepository, ProductRepository>();
services.AddScoped<IProductService, ProductService>();

// Example of injecting a service into a controller constructor
public class ProductsController : ControllerBase
{
    private readonly IProductService _productService;

    public ProductsController(IProductService productService)
    {
        _productService = productService;
    }

    // ... controller actions using _productService
}

Unit of Work Pattern

The Unit of Work pattern (often used in conjunction with the Repository pattern) manages a collection of repositories and coordinates the transaction for saving changes across multiple repositories to the data store. It ensures that all operations within a unit of work are completed successfully or none of them are.

Benefits: Atomicity of operations, reduced database round trips.

// Example interface for a Unit of Work
public interface IUnitOfWork : IDisposable
{
    IProductRepository Products { get; }
    ICategoryRepository Categories { get; }
    Task<int> SaveChangesAsync();
}