.NET Backend Patterns Skill

Purpose

Best practices for .NET 10 backend development with ASP.NET Core, Entity Framework Core, and clean architecture.

Auto-Invoke Triggers

• •Creating ASP.NET Core endpoints
• •Working with Entity Framework Core
• •Implementing Dependency Injection
• •Creating DTOs and validation

Project Structure (Clean Architecture)

src/
├── MyApp.Api/              # Web API, endpoints
├── MyApp.Application/      # Business logic, CQRS
├── MyApp.Domain/           # Entities, enums
└── MyApp.Infrastructure/   # EF Core, external services
tests/
├── MyApp.Application.Tests/
├── MyApp.Infrastructure.Tests/
└── MyApp.Api.Tests/

Layer Responsibilities

Entity Framework Core

DbContext Rules

• •Override SaveChangesAsync for audit fields
• •Use ApplyConfigurationsFromAssembly
• •Configure with IEntityTypeConfiguration<T>
• •Set Nullable enable in project

Configuration Best Practices

• •Define max lengths explicitly
• •Create indexes for query fields
• •Configure relationships explicitly
• •Use HasConversion for enums

Query Patterns

• •Use AsNoTracking() for read-only
• •Use Include() sparingly, prefer projections
• •Use AsSplitQuery() for multiple includes
• •Avoid N+1 with proper loading strategy

CQRS with MediatR

Command Pattern

• •One command per action
• •Command = request data
• •Handler = business logic
• •Validator = FluentValidation rules

Query Pattern

• •Queries are read-only
• •Return DTOs, not entities
• •Can skip validation often
• •Optimize for read performance

Pipeline Behaviors

• •ValidationBehavior - Run FluentValidation
• •LoggingBehavior - Log requests/responses
• •PerformanceBehavior - Log slow requests

Minimal API Endpoints

Organization

• •Group by feature/resource
• •Use extension methods: MapUserEndpoints()
• •Return IResult types
• •Use TypedResults for OpenAPI

Best Practices

• •Inject ISender for MediatR
• •Use [FromBody], [FromQuery] explicitly
• •Add .WithName(), .WithTags() for docs
• •Add .Produces<T>() for response types

Dependency Injection

Registration Patterns

• •Use extension methods per layer
• •Register scoped for request-lifetime
• •Register singleton for stateless services
• •Use IOptions<T> for configuration

Common Registrations

// Application layer
services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(assembly));
services.AddValidatorsFromAssembly(assembly);

// Infrastructure layer
services.AddDbContext<AppDbContext>(options => ...);
services.AddScoped<IRepository<T>, Repository<T>>();

Validation with FluentValidation

Validator Rules

• •One validator per request type
• •Use RuleFor() for each property
• •Use MustAsync() for DB checks
• •Inject repositories for uniqueness checks

Common Validations

• •NotEmpty() - Required fields
• •MaximumLength() - String limits
• •EmailAddress() - Email format
• •Matches() - Regex patterns

DTOs and Records

Naming Convention

Best Practices

• •Use record for immutability
• •Use required for mandatory props
• •Use init for optional props
• •Don't expose domain entities

Testing

Unit Tests

• •Test handlers in isolation
• •Mock repositories with Moq/NSubstitute
• •Use FluentAssertions for assertions
• •Follow naming: Method_Scenario_Expected

Integration Tests

• •Use WebApplicationFactory
• •Use in-memory database
• •Override DI registrations
• •Test full request pipeline

Best Practices

DO

• •Use record types for DTOs
• •Use nullable reference types
• •Use async/await throughout
• •Use FluentValidation
• •Use MediatR for CQRS
• •Separate concerns with layers

DON'T

• •Put business logic in endpoints
• •Use DateTime.Now (inject IDateTimeService)
• •Catch generic Exception
• •Mix sync and async
• •Expose domain entities from API
• •Hardcode connection strings

Code Quality