.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