.NET 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

3. Async/Await Patterns

// ✅ CORRECT: Async all the way down
public async Task<Product> GetProductAsync(string id, CancellationToken ct = default)
{
    return

4. Configuration with IOptions

// Configuration classes
public class CatalogOptions
{
    public const string SectionName = "Catalog";

    public

5. Result Pattern (Avoiding Exceptions for Flow Control)

// Generic Result type
public class Result<T>
{
    public bool IsSuccess

Data Access Patterns

Entity Framework Core

// DbContext configuration
public class AppDbContext : DbContext
{

Dapper for Performance

Caching Patterns

Multi-Level Cache with Redis

Testing Patterns

Unit Tests with xUnit and Moq

Integration Tests with WebApplicationFactory

public class ProductsApiTests : IClassFixture<WebApplicationFactory<Program>>
{
    private readonly WebApplicationFactory<

Best Practices

DO

1. Use async/await all the way through the call stack
2. Inject dependencies through constructor injection
3. Use IOptions for typed configuration
4. Return Result types instead of throwing exceptions for business logic
5. Use CancellationToken in all async methods
6. Prefer Dapper for read-heavy, performance-critical queries
7. Use EF Core for complex domain models with change tracking
8. Cache aggressively with proper invalidation strategies
9. Write unit tests for business logic, integration tests for APIs
10. Use record types for DTOs and immutable data

DON’T

1. Don’t block on async with .Result or .Wait()
2. Don’t use async void except for event handlers
3. Don’t catch generic Exception without re-throwing or logging
4. Don’t hardcode configuration values
5. Don’t expose EF entities directly in APIs (use DTOs)
6. Don’t forget AsNoTracking() for read-only queries
7. Don’t ignore CancellationToken parameters
8. Don’t create new HttpClient() manually (use IHttpClientFactory)
9. Don’t mix sync and async code unnecessarily
10. Don’t skip validation at API boundaries

Common Pitfalls

• N+1 Queries: Use .Include() or explicit joins
• Memory Leaks: Dispose IDisposable resources, use using
• Deadlocks: Don’t mix sync and async, use ConfigureAwait(false) in libraries
• Over-fetching: Select only needed columns, use projections
• Missing Indexes: Check query plans, add indexes for common filters
• Timeout Issues: Configure appropriate timeouts for HTTP clients
• Cache Stampede: Use distributed locks for cache population