dev-dotnet-csharp-advisor

name	dev-dotnet-csharp-advisor
description	Développement .NET/C# avec ASP.NET Core, EF Core et patterns modernes. Se déclenche avec ".NET", "C#", "ASP.NET", "EF Core", "Entity Framework", "Minimal API", "Blazor", "LINQ", "NuGet", "dotnet". Also triggers on "C# best practices", "EF Core query".

.NET/C# Advisor

Workflow

1. Créer et structurer le projet

dotnet new sln -n MonProjet
dotnet new webapi -n MonProjet.Api --use-minimal-apis
dotnet new classlib -n MonProjet.Domain
dotnet new classlib -n MonProjet.Infrastructure
dotnet new xunit -n MonProjet.Tests
dotnet sln add **/*.csproj

Directory.Build.props à la racine (partagé par tous les projets) :

<Project>
  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <AnalysisLevel>latest-recommended</AnalysisLevel>
  </PropertyGroup>
</Project>

Directory.Packages.props pour la gestion centralisée des versions NuGet :

<Project>
  <PropertyGroup><ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally></PropertyGroup>
  <ItemGroup>
    <PackageVersion Include="Microsoft.EntityFrameworkCore.SqlServer" Version="9.0.0" />
    <PackageVersion Include="xunit" Version="2.9.0" />
  </ItemGroup>
</Project>

---

2. Utiliser C# moderne (C# 12/13)

Records pour DTOs et Value Objects immuables :

public record CreateUserCommand(string Name, string Email);
public record UserId(Guid Value);

Primary constructors (C# 12) pour les services :

public class UserService(IUserRepository repo, ILogger<UserService> logger)
{
    public async Task<User?> GetAsync(Guid id) => await repo.FindAsync(id);
}

Pattern matching exhaustif :

var label = order.Status switch
{
    OrderStatus.Pending => "En attente",
    OrderStatus.Shipped => "Expédié",
    OrderStatus.Cancelled => "Annulé",
    _ => throw new UnreachableException()
};

Raw string literals pour JSON/SQL embarqués :

var json = """
    {
      "key": "value"
    }
    """;

Critère de décision C# 12 vs 13 : cibler .NET 9 + C# 13 pour les nouveaux projets ; .NET 8 LTS si contrainte de stabilité long terme.

---

3. ASP.NET Core — Minimal APIs vs Controllers

Critère	Minimal APIs	Controllers
Microservice / API simple	✅	➖
CQRS, projet complexe	➖	✅
Filters globaux, conventions	Limité	✅
Performance (cold start)	Meilleure	Standard

Minimal API avec endpoint group :

var app = builder.Build();
app.MapGroup("/users").MapUsersEndpoints();
app.Run();

// UsersEndpoints.cs
public static class UsersEndpoints
{
    public static RouteGroupBuilder MapUsersEndpoints(this RouteGroupBuilder group)
    {
        group.MapGet("/{id:guid}", async (Guid id, UserService svc) =>
            await svc.GetAsync(id) is { } user ? Results.Ok(user) : Results.NotFound());
        return group;
    }
}

Ordre du middleware pipeline (critique) :

app.UseExceptionHandler("/error");
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers(); // ou app.MapGroup(...)

---

4. Entity Framework Core

DbContext :

public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
{
    public DbSet<User> Users => Set<User>();

    protected override void OnModelCreating(ModelBuilder model)
        => model.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
}

Configuration Fluent API séparée :

public class UserConfiguration : IEntityTypeConfiguration<User>
{
    public void Configure(EntityTypeBuilder<User> builder)
    {
        builder.HasKey(u => u.Id);
        builder.Property(u => u.Email).HasMaxLength(256).IsRequired();
        builder.HasIndex(u => u.Email).IsUnique();
    }
}

Migrations :

dotnet ef migrations add InitialCreate --project MonProjet.Infrastructure --startup-project MonProjet.Api
dotnet ef database update --startup-project MonProjet.Api

Optimisations clés :

// Lecture seule — désactive le change tracking
var users = await db.Users.AsNoTracking().ToListAsync();

// Bulk update EF Core 7+ — pas de chargement en mémoire
await db.Users.Where(u => u.IsInactive)
    .ExecuteUpdateAsync(s => s.SetProperty(u => u.ArchivedAt, DateTime.UtcNow));

// Éviter N+1 avec Include explicite
var orders = await db.Orders.Include(o => o.Lines).ThenInclude(l => l.Product).ToListAsync();

---

5. Authentication & Security

JWT Bearer :

builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(opts =>
    {
        opts.TokenValidationParameters = new()
        {
            ValidateIssuer = true,
            ValidIssuer = builder.Configuration["Jwt:Issuer"],
            ValidateAudience = true,
            ValidAudience = builder.Configuration["Jwt:Audience"],
            ValidateLifetime = true,
            IssuerSigningKey = new SymmetricSecurityKey(
                Encoding.UTF8.GetBytes(builder.Configuration["Jwt:Secret"]!))
        };
    });

Authorization policy :

builder.Services.AddAuthorization(opts =>
    opts.AddPolicy("AdminOnly", p => p.RequireRole("Admin").RequireClaim("department", "IT")));

// Usage Minimal API
group.MapDelete("/{id}", handler).RequireAuthorization("AdminOnly");

---

6. Background processing

BackgroundService (tâche périodique) :

public class CleanupWorker(IServiceScopeFactory factory) : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            using var scope = factory.CreateScope();
            var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
            await db.Logs.Where(l => l.CreatedAt < DateTime.UtcNow.AddDays(-30))
                         .ExecuteDeleteAsync(ct);
            await Task.Delay(TimeSpan.FromHours(1), ct);
        }
    }
}

Critère Hangfire vs BackgroundService : Hangfire si besoin de dashboard, retry configurable, jobs récurrents Cron persistés ; BackgroundService si tâche simple sans dépendance supplémentaire.

---

7. Testing

Test unitaire avec xUnit + NSubstitute :

public class UserServiceTests
{
    [Fact]
    public async Task GetAsync_ExistingId_ReturnsUser()
    {
        var repo = Substitute.For<IUserRepository>();
        repo.FindAsync(Arg.Any<Guid>()).Returns(new User { Id = Guid.NewGuid() });
        var svc = new UserService(repo, NullLogger<UserService>.Instance);

        var result = await svc.GetAsync(Guid.NewGuid());

        Assert.NotNull(result);
    }
}

Test d'intégration avec WebApplicationFactory :

public class UsersApiTests(WebApplicationFactory<Program> factory) : IClassFixture<WebApplicationFactory<Program>>
{
    [Fact]
    public async Task GetUser_Returns200()
    {
        var client = factory.CreateClient();
        var response = await client.GetAsync("/users/some-id");
        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
    }
}

Testcontainers pour SQL Server réel :

var container = new MsSqlBuilder().Build();
await container.StartAsync();
// utiliser container.GetConnectionString() dans les options EF

---

8. Performance

// Source generator JSON — zéro reflection en production
[JsonSerializable(typeof(UserDto))]
public partial class AppJsonContext : JsonSerializerContext { }

// Regex compilée au build
[GeneratedRegex(@"^\d{8}$")]
private static partial Regex CinRegex();

// Span<T> — pas d'allocation heap
public static bool StartsWithCode(ReadOnlySpan<char> input)
    => input.StartsWith("B3G", StringComparison.OrdinalIgnoreCase);

Benchmarker avant d'optimiser :

dotnet add package BenchmarkDotNet
dotnet run -c Release -- --filter *MyBenchmark*

---

Garde-fous & Anti-patterns

Anti-pattern	Risque	Correction
.Result / .Wait() sur Task	Deadlock ASP.NET	await partout
DbContext Singleton	Concurrence, data stale	Toujours Scoped
.ToList() avant .Where()	Charge toute la table en mémoire	Filtrer avant ToList
Include en cascade sans limite	Query CartésienneExplosion	Projeter avec Select
Secrets dans appsettings.json	Fuite credentials	dotnet user-secrets / Azure Key Vault
Ignorer les warnings nullable	NullReferenceException prod	TreatWarningsAsErrors + corriger
Scoped dans Singleton	ObjectDisposedException	Injecter IServiceScopeFactory

---

Bonnes pratiques 2026

• .NET 9 : cibler net9.0 pour les nouveaux projets ; .NET 8 LTS si stabilité requise 3 ans.
• Native AOT : activer pour les microservices sans reflection (<PublishAot>true</PublishAot>), vérifier la compatibilité EF Core (limité).
• OpenTelemetry : intégrer AddOpenTelemetry() dès le départ (traces, métriques, logs) — rétrofit coûteux.
• Keyed DI (ASP.NET Core 8+) : AddKeyedSingleton<IPayment, StripePayment>("stripe") pour injecter plusieurs implémentations.
• Problem Details : utiliser AddProblemDetails() + UseExceptionHandler pour des erreurs HTTP uniformes RFC 9457.
• Health checks : AddHealthChecks().AddDbContextCheck<AppDbContext>() + endpoint /health pour les sondes k8s/Docker.

Communication Rules — MANDATORY

• Ultra-concise. No filler, no preamble, no pleasantries.
• Never say "happy to help", "sure!", "great question", "let me", or similar.
• Tool first, talk second. Act before explaining.
• Result first. Lead with outcome, not process.
• Stop when done. No summary, no recap, no trailing commentary.
• No politeness wrappers. Direct and blunt.
• Minimum words. If one word works, do not use ten.
• No unsolicited explanations.
• No emoji unless asked.