dotnet-core-expert

SKILL.md

.NET Core Expert

Core Workflow

Analyze requirements — Identify architecture pattern, data models, API design

Design solution — Create clean architecture layers with proper separation

Implement — Write high-performance code with modern C# features; run dotnet build to verify compilation — if build fails, review errors, fix issues, and rebuild before proceeding

Secure — Add authentication, authorization, and security best practices

Test — Write comprehensive tests with xUnit and integration testing; run dotnet test to confirm all tests pass — if tests fail, diagnose failures, fix the implementation, and re-run before continuing; verify endpoints with curl or a REST client

Reference Guide

Load detailed guidance based on context:

Topic
Reference
Load When

Minimal APIs
references/minimal-apis.md
Creating endpoints, routing, middleware

Clean Architecture
references/clean-architecture.md
CQRS, MediatR, layers, DI patterns

Entity Framework
references/entity-framework.md
DbContext, migrations, relationships

Authentication
references/authentication.md
JWT, Identity, authorization policies

Cloud-Native
references/cloud-native.md
Docker, health checks, configuration

Constraints

MUST DO

Use .NET 8 and C# 12 features

Enable nullable reference types: <Nullable>enable</Nullable> in the .csproj

Use async/await for all I/O operations — e.g., await dbContext.Users.ToListAsync()

Implement proper dependency injection

Use record types for DTOs — e.g., public record UserDto(int Id, string Name);

Follow clean architecture principles

Write integration tests with WebApplicationFactory<Program>

Configure OpenAPI/Swagger documentation

MUST NOT DO

Use synchronous I/O operations

Expose entities directly in API responses

Skip input validation

Use legacy .NET Framework patterns

Mix concerns across architectural layers

Use deprecated EF Core patterns

Code Examples

Minimal API Endpoint

// Program.cs
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(typeof(Program).Assembly));

var app = builder.Build();
app.UseSwagger();
app.UseSwaggerUI();

app.MapGet("/users/{id}", async (int id, ISender sender, CancellationToken ct) =>
{
    var result = await sender.Send(new GetUserQuery(id), ct);
    return result is null ? Results.NotFound() : Results.Ok(result);
})
.WithName("GetUser")
.Produces<UserDto>()
.ProducesProblem(404);

app.Run();

MediatR Query Handler

// Application/Users/GetUserQuery.cs
public record GetUserQuery(int Id) : IRequest<UserDto?>;

public sealed class GetUserQueryHandler : IRequestHandler<GetUserQuery, UserDto?>
{
    private readonly AppDbContext _db;

    public GetUserQueryHandler(AppDbContext db) => _db = db;

    public async Task<UserDto?> Handle(GetUserQuery request, CancellationToken ct) =>
        await _db.Users
            .AsNoTracking()
            .Where(u => u.Id == request.Id)
            .Select(u => new UserDto(u.Id, u.Name))
            .FirstOrDefaultAsync(ct);
}

EF Core DbContext with Async Query

// Infrastructure/AppDbContext.cs
public sealed class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
{
    public DbSet<User> Users => Set<User>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
    }
}

// Usage in a service
public async Task<IReadOnlyList<UserDto>> GetAllAsync(CancellationToken ct) =>
    await _db.Users
        .AsNoTracking()
        .Select(u => new UserDto(u.Id, u.Name))
        .ToListAsync(ct);

DTO with Record Type

public record UserDto(int Id, string Name);
public record CreateUserRequest(string Name, string Email);

Output Templates

When implementing .NET features, provide:

Project structure (solution/project files)

Domain models and DTOs

API endpoints or service implementations

Database context and migrations if applicable

Brief explanation of architectural decisions

Documentation
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