Dotnet backend patterns

Skill tranhieutt/software_development_department/.claude/skills/dotnet-backend-patterns

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Provides .NET and ASP.NET Core patterns for REST APIs, Entity Framework, dependency injection, and middleware. Use when working with C# files (*.cs, *.csproj) or when the user mentions .NET, ASP.NET Core, C#, or Entity Framework.

SKILL.md

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.NET Backend Development Patterns

C#/.NET patterns for production-grade APIs, MCP servers, and enterprise backends.

API Structure (Minimal API + Controllers)

```csharp // Program.cs - Minimal API var builder = WebApplication.CreateBuilder(args); builder.Services.AddDbContext<AppDbContext>(o => o.UseNpgsql(connStr)); builder.Services.AddScoped<IOrderService, OrderService>();

var app = builder.Build(); app.MapGet("/orders/{id}", async (int id, IOrderService svc) => await svc.GetByIdAsync(id) is { } order ? Results.Ok(order) : Results.NotFound()); ```

Dependency Injection Patterns

```csharp // Register services builder.Services.AddScoped<IPaymentService, StripePaymentService>(); builder.Services.AddSingleton<ICacheService, RedisCacheService>(); builder.Services.AddHttpClient<IApiClient, ExternalApiClient>(client => { client.BaseAddress = new Uri("https://api.external.com"); }); ```

Lifetime guide: Singleton (stateless/cache), Scoped (per-request), Transient (stateless utility).

Entity Framework Core

```csharp // DbContext with conventions public class AppDbContext : DbContext { public DbSet<Order> Orders => Set<Order>(); protected override void OnModelCreating(ModelBuilder builder) { builder.Entity<Order>().HasIndex(o => o.UserId); builder.Entity<Order>().Property(o => o.Total).HasPrecision(18, 2); } } ```

Performance tips:

Use .AsNoTracking() for read-only queries
Avoid N+1 with .Include() or projection
Use compiled queries for hot paths

Middleware Pipeline

```csharp app.UseMiddleware<RequestLoggingMiddleware>(); app.UseAuthentication(); app.UseAuthorization(); app.UseRateLimiter(); app.MapControllers(); ```

Error Handling

```csharp // Global exception handler app.UseExceptionHandler(err => err.Run(async context => { var exception = context.Features.Get<IExceptionHandlerFeature>()?.Error; var (status, message) = exception switch { NotFoundException => (404, exception.Message), UnauthorizedAccessException => (403, "Forbidden"), _ => (500, "Internal server error") }; context.Response.StatusCode = status; await context.Response.WriteAsJsonAsync(new { error = message }); })); ```

Configuration (IOptions pattern)

```csharp builder.Services.Configure<StripeSettings>( builder.Configuration.GetSection("Stripe"));

// Usage public class PaymentService(IOptions<StripeSettings> opts) { private readonly string _key = opts.Value.SecretKey; } ```

Testing

```csharp // Integration test with WebApplicationFactory public class OrderApiTests : IClassFixture<WebApplicationFactory<Program>> { private readonly HttpClient _client; [Fact] public async Task GetOrder_ReturnsOk() { var response = await _client.GetAsync("/orders/1"); response.StatusCode.Should().Be(HttpStatusCode.OK); } } ```

Related Skills

backend-architect — architecture decisions
database-architect — schema design
drizzle-orm-expert — Node.js ORM alternative

Gives 1 of the 12 instructions most data backend skills give in 686 tokens

Counted across 229 of the 229 authors here whose files we hold, read 2026-08-07

separate business logic into service layersin 22 of 229, across 15 files
retry failures with exponential backoffin 21 of 229, across 14 files
select only needed database columnsin 20 of 229, across 13 files
abstract data access into repository classesin 19 of 229, across 12 files
use centralized error handlersin 17 of 229, across 10 files
Use AsNoTracking for read-only querieshere, and in 16 of 229, across 4 files
Use async/await for all I/O operationsin 16 of 229, across 5 files
implement structured loggingin 15 of 229, across 4 files
Use dependency injection for all servicesin 14 of 229, across 2 files
use resource-based URLs for REST APIsin 13 of 229, across 7 files
invalidate cache after data changesin 13 of 229, across 9 files
Use a dependency injection containerin 12 of 229, across 4 files

Said here and by no other author read

Avoid N+1 queries using Include or projection
Use compiled queries for hot paths
Write integration tests with WebApplicationFactory
Register HttpClient with AddHttpClient
Use global exception handlers
Register dependencies using service lifetimes

Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once. Length counted with cl100k_base; the agent that loads this file may tokenize it differently.