dotnet-backend-patterns

.NET Backend Development Patterns

Master C#/.NET patterns for building production-grade APIs, MCP servers, and enterprise backends with modern best practices (2024/2025).

When to Use This Skill

• Developing new .NET Web APIs or MCP servers
• Reviewing C# code for quality and performance
• Designing service architectures with dependency injection
• Implementing caching strategies with Redis
• Writing unit and integration tests
• Optimizing database access with EF Core or Dapper
• Configuring applications with IOptions pattern
• Handling errors and implementing resilience patterns

Core Concepts

1. Project Structure (Clean Architecture)

src/
├── Domain/                     # Core business logic (no dependencies)
│   ├── Entities/
│   ├── Interfaces/
│   ├── Exceptions/
│   └── ValueObjects/
├── Application/                # Use cases, DTOs, validation
│   ├── Services/
│   ├── DTOs/
│   ├── Validators/
│   └── Interfaces/
├── Infrastructure/             # External implementations
│   ├── Data/                   # EF Core, Dapper repositories
│   ├── Caching/                # Redis, Memory cache
│   ├── External/               # HTTP clients, third-party APIs
│   └── DependencyInjection/    # Service registration
└── Api/                        # Entry point
    ├── Controllers/            # Or MinimalAPI endpoints
    ├── Middleware/
    ├── Filters/
    └── Program.cs

2. Dependency Injection Patterns

// Service registration by lifetime
public static class ServiceCollectionExtensions
{
    public static IServiceCollection AddApplicationServices(
        this IServiceCollection services,
        IConfiguration configuration)
    {
        // Scoped: One instance per HTTP request
        services.AddScoped<IProductService, ProductService>();
        services.AddScoped<IOrderService, OrderService>();

        // Singleton: One instance for app lifetime
        services.AddSingleton<ICacheService, RedisCacheService>();
        services.AddSingleton<IConnectionMultiplexer>(_ =>
            ConnectionMultiplexer.Connect(configuration["Redis:Connection"]!));

        // Transient: New instance every time
        services.AddTransient<IValidator<CreateOrderRequest>, CreateOrderValidator>();

        // Options pattern for configuration
        services.Configure<CatalogOptions>(configuration.GetSection("Catalog"));
        services.Configure<RedisOptions>(configuration.GetSection("Redis"));

        // Factory pattern for conditional creation
        services.AddScoped<IPriceCalculator>(sp =>
        {
            var options = sp.GetRequiredService<IOptions<PricingOptions>>().Value;
            return options.UseNewEngine
                ? sp.GetRequiredService<NewPriceCalculator>()
                : sp.GetRequiredService<LegacyPriceCalculator>();
        });

        // Keyed services (.NET 8+)
        services.AddKeyedScoped<IPaymentProcessor, StripeProcessor>("stripe");
        services.AddKeyedScoped<IPaymentProcessor, PayPalProcessor>("paypal");

        return services;
    }
}

// Usage with keyed services
public class CheckoutService
{
    public CheckoutService(
        [FromKeyedServices("stripe")] IPaymentProcessor stripeProcessor)
    {
        _processor = stripeProcessor;
    }
}