--- name: dotnet-core-expert description: Use when building .NET 8 applications with minimal APIs, clean architecture, or cloud-native microservices. Invoke for Entity Framework Core, CQRS with MediatR, JWT authentication, AOT compilation. license: MIT metadata: author: https://github.com/Jeffallan version: "1.1.0" domain: backend triggers: .NET Core, .NET 8, ASP.NET Core, C# 12, minimal API, Entity Framework Core, microservices .NET, CQRS, MediatR role: specialist scope: implementation output-format: code related-skills: fullstack-guardian, microservices-architect, cloud-architect, test-master --- # .NET Core Expert ## Core Workflow 1. **Analyze requirements** — Identify architecture pattern, data models, API design 2. **Design solution** — Create clean architecture layers with proper separation 3. **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 4. **Secure** — Add authentication, authorization, and security best practices 5. **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: `enable` 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` - 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 ```csharp // 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() .ProducesProblem(404); app.Run(); ``` ### MediatR Query Handler ```csharp // Application/Users/GetUserQuery.cs public record GetUserQuery(int Id) : IRequest; public sealed class GetUserQueryHandler : IRequestHandler { private readonly AppDbContext _db; public GetUserQueryHandler(AppDbContext db) => _db = db; public async Task 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 ```csharp // Infrastructure/AppDbContext.cs public sealed class AppDbContext(DbContextOptions options) : DbContext(options) { public DbSet Users => Set(); protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly); } } // Usage in a service public async Task> GetAllAsync(CancellationToken ct) => await _db.Users .AsNoTracking() .Select(u => new UserDto(u.Id, u.Name)) .ToListAsync(ct); ``` ### DTO with Record Type ```csharp public record UserDto(int Id, string Name); public record CreateUserRequest(string Name, string Email); ``` ## Output Templates When implementing .NET features, provide: 1. Project structure (solution/project files) 2. Domain models and DTOs 3. API endpoints or service implementations 4. Database context and migrations if applicable 5. Brief explanation of architectural decisions

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