# .NET 8: Een API bouwen met ASP.NET Core

> Volledige gids voor het bouwen van een professionele REST API met .NET 8 en ASP.NET Core. Controllers, Entity Framework Core, validatie en best practices uitgelegd.

- Published: 2026-01-17
- Updated: 2026-04-10
- Author: SharpSkill
- Tags: dotnet, aspnet core, csharp, rest api, entity framework
- Reading time: 14 min

---

.NET 8 is een belangrijke release van het Microsoft-framework en brengt aanzienlijke verbeteringen op het gebied van performance en productiviteit voor API-ontwikkeling. ASP.NET Core combineert de kracht van C# met een moderne, modulaire architectuur die ideaal is voor enterprise-applicaties. Deze gids behandelt het volledige proces van het bouwen van een professionele REST API, van de initiele setup tot productie-klare code.

> **.NET 8 LTS**
>
> .NET 8 is een Long-Term Support (LTS) release met 3 jaar ondersteuning. Verbeteringen aan Minimal APIs en Native AOT maken het een optimale keuze voor microservices en cloud-native applicaties.

## Initiele Projectconfiguratie met .NET 8

Het aanmaken van een ASP.NET Core API-project gebeurt via de .NET CLI, die een geoptimaliseerde projectstructuur genereert. De configuratie van essentiele NuGet-pakketten legt de basis voor de ontwikkeling.

```bash
# terminal
# Check installed .NET version
dotnet --version
# Expected: 8.0.x

# Create the API project
dotnet new webapi -n ProductApi -o ProductApi
cd ProductApi

# Add essential packages
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package FluentValidation.AspNetCore
dotnet add package Swashbuckle.AspNetCore
```

Deze commando's maken een API-project aan met de benodigde afhankelijkheden voor Entity Framework Core, validatie en Swagger-documentatie.

```csharp
// Program.cs
using Microsoft.EntityFrameworkCore;
using ProductApi.Data;
using ProductApi.Services;
using FluentValidation;
using FluentValidation.AspNetCore;

var builder = WebApplication.CreateBuilder(args);

// Configure Entity Framework Core with SQL Server
builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

// Register business services
builder.Services.AddScoped<IProductService, ProductService>();
builder.Services.AddScoped<ICategoryService, CategoryService>();

// Configure controllers with validation
builder.Services.AddControllers();
builder.Services.AddFluentValidationAutoValidation();
builder.Services.AddValidatorsFromAssemblyContaining<Program>();

// Configure Swagger for documentation
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new() { Title = "Product API", Version = "v1" });
});

var app = builder.Build();

// Middleware pipeline
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();

app.Run();
```

Deze configuratie maakt gebruik van het Minimal API-patroon van .NET 8, terwijl controllers behouden blijven voor een overzichtelijke en onderhoudbare structuur.

## Datamodellen en Entity Framework Core

Modellen vertegenwoordigen de business-entiteiten van de applicatie. Entity Framework Core verzorgt de object-relationele mapping met fluent configuratie en slimme conventies.

```csharp
// Models/Product.cs
namespace ProductApi.Models;

public class Product
{
    // Primary key with auto-increment
    public int Id { get; set; }

    // Required properties (non-nullable in C# 8+)
    public required string Name { get; set; }
    public required string Description { get; set; }

    // Price with decimal precision
    public decimal Price { get; set; }

    // Stock with default value
    public int StockQuantity { get; set; } = 0;

    // Product status
    public bool IsActive { get; set; } = true;

    // Relationship with Category (foreign key)
    public int CategoryId { get; set; }
    public Category? Category { get; set; }

    // Automatic tracking dates
    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public DateTime? UpdatedAt { get; set; }
}
```

Het `required` keyword uit C# 11 zorgt ervoor dat essentiele properties altijd geinitialiseerd worden bij het aanmaken.

```csharp
// Models/Category.cs
namespace ProductApi.Models;

public class Category
{
    public int Id { get; set; }

    public required string Name { get; set; }

    // Slug for friendly URLs
    public required string Slug { get; set; }

    public string? Description { get; set; }

    // Inverse navigation: list of products in this category
    public ICollection<Product> Products { get; set; } = new List<Product>();

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
}
```

```csharp
// Data/AppDbContext.cs
using Microsoft.EntityFrameworkCore;
using ProductApi.Models;

namespace ProductApi.Data;

public class AppDbContext : DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
    {
    }

    // DbSets for each entity
    public DbSet<Product> Products => Set<Product>();
    public DbSet<Category> Categories => Set<Category>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Product entity configuration
        modelBuilder.Entity<Product>(entity =>
        {
            // Index on name for fast search
            entity.HasIndex(p => p.Name);

            // Price precision: 18 digits, 2 decimals
            entity.Property(p => p.Price)
                .HasPrecision(18, 2);

            // Relationship with Category
            entity.HasOne(p => p.Category)
                .WithMany(c => c.Products)
                .HasForeignKey(p => p.CategoryId)
                .OnDelete(DeleteBehavior.Restrict);
        });

        // Category entity configuration
        modelBuilder.Entity<Category>(entity =>
        {
            // Unique slug
            entity.HasIndex(c => c.Slug).IsUnique();

            // Maximum name length
            entity.Property(c => c.Name).HasMaxLength(100);
        });
    }
}
```

De Fluent API-configuratie biedt nauwkeurige controle over het databaseschema dat door EF Core-migraties wordt gegenereerd.

> **Entity Framework Core Migrations**
>
> Migraties versioneren het databaseschema. Voer `dotnet ef migrations add InitialCreate` uit, gevolgd door `dotnet ef database update` om de wijzigingen toe te passen.

## DTO's en Validatie met FluentValidation

DTO's (Data Transfer Objects) scheiden domeinmodellen van de data die via de API wordt blootgesteld. FluentValidation biedt declaratieve en onderhoudbare validatie.

```csharp
// DTOs/ProductDtos.cs
namespace ProductApi.DTOs;

// DTO for product creation
public record CreateProductDto(
    string Name,
    string Description,
    decimal Price,
    int StockQuantity,
    int CategoryId
);

// DTO for product update
public record UpdateProductDto(
    string? Name,
    string? Description,
    decimal? Price,
    int? StockQuantity,
    bool? IsActive
);

// DTO for response (read)
public record ProductDto(
    int Id,
    string Name,
    string Description,
    decimal Price,
    int StockQuantity,
    bool IsActive,
    string CategoryName,
    DateTime CreatedAt
);

// DTO for list with pagination
public record ProductListDto(
    int Id,
    string Name,
    decimal Price,
    int StockQuantity,
    bool IsActive,
    string CategoryName
);
```

Het gebruik van C# 9+ records maakt DTO's onveranderlijk en beknopt, met automatische waardegelijkheid.

```csharp
// Validators/ProductValidators.cs
using FluentValidation;
using ProductApi.DTOs;

namespace ProductApi.Validators;

public class CreateProductValidator : AbstractValidator<CreateProductDto>
{
    public CreateProductValidator()
    {
        // Name is required and limited to 200 characters
        RuleFor(x => x.Name)
            .NotEmpty().WithMessage("Product name is required.")
            .MaximumLength(200).WithMessage("Name cannot exceed 200 characters.");

        // Description required with minimum length
        RuleFor(x => x.Description)
            .NotEmpty().WithMessage("Description is required.")
            .MinimumLength(10).WithMessage("Description must contain at least 10 characters.");

        // Positive price required
        RuleFor(x => x.Price)
            .GreaterThan(0).WithMessage("Price must be greater than 0.")
            .LessThanOrEqualTo(999999.99m).WithMessage("Maximum price is 999,999.99.");

        // Non-negative stock
        RuleFor(x => x.StockQuantity)
            .GreaterThanOrEqualTo(0).WithMessage("Stock cannot be negative.");

        // Valid category
        RuleFor(x => x.CategoryId)
            .GreaterThan(0).WithMessage("A valid category is required.");
    }
}

public class UpdateProductValidator : AbstractValidator<UpdateProductDto>
{
    public UpdateProductValidator()
    {
        // Conditional validation: only if value is provided
        RuleFor(x => x.Name)
            .MaximumLength(200)
            .When(x => !string.IsNullOrEmpty(x.Name));

        RuleFor(x => x.Price)
            .GreaterThan(0)
            .When(x => x.Price.HasValue);

        RuleFor(x => x.StockQuantity)
            .GreaterThanOrEqualTo(0)
            .When(x => x.StockQuantity.HasValue);
    }
}
```

FluentValidation integreert automatisch met de ASP.NET Core-validatiepipeline en retourneert gestructureerde 400-fouten.

## Business Services en Abstractielaag

De servicelaag kapselt bedrijfslogica en databasebewerkingen in, wat testen en onderhoud vergemakkelijkt.

```csharp
// Services/IProductService.cs
using ProductApi.DTOs;

namespace ProductApi.Services;

public interface IProductService
{
    // Retrieval with pagination
    Task<(IEnumerable<ProductListDto> Items, int TotalCount)> GetAllAsync(
        int page = 1,
        int pageSize = 10,
        string? search = null,
        int? categoryId = null);

    // Retrieval by ID
    Task<ProductDto?> GetByIdAsync(int id);

    // Creation
    Task<ProductDto> CreateAsync(CreateProductDto dto);

    // Update
    Task<ProductDto?> UpdateAsync(int id, UpdateProductDto dto);

    // Deletion
    Task<bool> DeleteAsync(int id);
}
```

```csharp
// Services/ProductService.cs
using Microsoft.EntityFrameworkCore;
using ProductApi.Data;
using ProductApi.DTOs;
using ProductApi.Models;

namespace ProductApi.Services;

public class ProductService : IProductService
{
    private readonly AppDbContext _context;

    public ProductService(AppDbContext context)
    {
        _context = context;
    }

    public async Task<(IEnumerable<ProductListDto> Items, int TotalCount)> GetAllAsync(
        int page = 1,
        int pageSize = 10,
        string? search = null,
        int? categoryId = null)
    {
        // Build base query
        var query = _context.Products
            .Include(p => p.Category)
            .AsQueryable();

        // Filter by text search
        if (!string.IsNullOrWhiteSpace(search))
        {
            query = query.Where(p =>
                p.Name.Contains(search) ||
                p.Description.Contains(search));
        }

        // Filter by category
        if (categoryId.HasValue)
        {
            query = query.Where(p => p.CategoryId == categoryId.Value);
        }

        // Total count before pagination
        var totalCount = await query.CountAsync();

        // Apply pagination
        var items = await query
            .OrderByDescending(p => p.CreatedAt)
            .Skip((page - 1) * pageSize)
            .Take(pageSize)
            .Select(p => new ProductListDto(
                p.Id,
                p.Name,
                p.Price,
                p.StockQuantity,
                p.IsActive,
                p.Category!.Name))
            .ToListAsync();

        return (items, totalCount);
    }

    public async Task<ProductDto?> GetByIdAsync(int id)
    {
        // Retrieve with category inclusion
        var product = await _context.Products
            .Include(p => p.Category)
            .FirstOrDefaultAsync(p => p.Id == id);

        if (product == null) return null;

        // Map to DTO
        return new ProductDto(
            product.Id,
            product.Name,
            product.Description,
            product.Price,
            product.StockQuantity,
            product.IsActive,
            product.Category?.Name ?? "Uncategorized",
            product.CreatedAt);
    }

    public async Task<ProductDto> CreateAsync(CreateProductDto dto)
    {
        // Create entity
        var product = new Product
        {
            Name = dto.Name,
            Description = dto.Description,
            Price = dto.Price,
            StockQuantity = dto.StockQuantity,
            CategoryId = dto.CategoryId
        };

        // Add and save
        _context.Products.Add(product);
        await _context.SaveChangesAsync();

        // Load category for response
        await _context.Entry(product)
            .Reference(p => p.Category)
            .LoadAsync();

        return new ProductDto(
            product.Id,
            product.Name,
            product.Description,
            product.Price,
            product.StockQuantity,
            product.IsActive,
            product.Category?.Name ?? "Uncategorized",
            product.CreatedAt);
    }

    public async Task<ProductDto?> UpdateAsync(int id, UpdateProductDto dto)
    {
        // Retrieve existing entity
        var product = await _context.Products
            .Include(p => p.Category)
            .FirstOrDefaultAsync(p => p.Id == id);

        if (product == null) return null;

        // Conditional field updates
        if (!string.IsNullOrEmpty(dto.Name))
            product.Name = dto.Name;

        if (!string.IsNullOrEmpty(dto.Description))
            product.Description = dto.Description;

        if (dto.Price.HasValue)
            product.Price = dto.Price.Value;

        if (dto.StockQuantity.HasValue)
            product.StockQuantity = dto.StockQuantity.Value;

        if (dto.IsActive.HasValue)
            product.IsActive = dto.IsActive.Value;

        // Update modification date
        product.UpdatedAt = DateTime.UtcNow;

        await _context.SaveChangesAsync();

        return new ProductDto(
            product.Id,
            product.Name,
            product.Description,
            product.Price,
            product.StockQuantity,
            product.IsActive,
            product.Category?.Name ?? "Uncategorized",
            product.CreatedAt);
    }

    public async Task<bool> DeleteAsync(int id)
    {
        // Direct deletion without prior loading
        var result = await _context.Products
            .Where(p => p.Id == id)
            .ExecuteDeleteAsync();

        return result > 0;
    }
}
```

Het gebruik van `ExecuteDeleteAsync` (nieuw in EF Core 7+) verbetert de performance doordat het laden van de entiteit voor verwijdering wordt overgeslagen.

## API Controllers en REST Endpoints

Controllers stellen REST-endpoints beschikbaar en orchestreren aanroepen naar business services met passende HTTP-statuscode-afhandeling.

```csharp
// Controllers/ProductsController.cs
using Microsoft.AspNetCore.Mvc;
using ProductApi.DTOs;
using ProductApi.Services;

namespace ProductApi.Controllers;

[ApiController]
[Route("api/[controller]")]
[Produces("application/json")]
public class ProductsController : ControllerBase
{
    private readonly IProductService _productService;

    public ProductsController(IProductService productService)
    {
        _productService = productService;
    }

    /// <summary>
    /// Retrieves the list of products with pagination and filters.
    /// </summary>
    [HttpGet]
    [ProducesResponseType(typeof(PaginatedResponse<ProductListDto>), StatusCodes.Status200OK)]
    public async Task<IActionResult> GetAll(
        [FromQuery] int page = 1,
        [FromQuery] int pageSize = 10,
        [FromQuery] string? search = null,
        [FromQuery] int? categoryId = null)
    {
        // Validate pagination parameters
        if (page < 1) page = 1;
        if (pageSize < 1 || pageSize > 100) pageSize = 10;

        var (items, totalCount) = await _productService.GetAllAsync(
            page, pageSize, search, categoryId);

        // Standardized paginated response
        var response = new PaginatedResponse<ProductListDto>
        {
            Items = items,
            Page = page,
            PageSize = pageSize,
            TotalCount = totalCount,
            TotalPages = (int)Math.Ceiling(totalCount / (double)pageSize)
        };

        return Ok(response);
    }

    /// <summary>
    /// Retrieves a product by its identifier.
    /// </summary>
    [HttpGet("{id:int}")]
    [ProducesResponseType(typeof(ProductDto), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<IActionResult> GetById(int id)
    {
        var product = await _productService.GetByIdAsync(id);

        if (product == null)
        {
            return NotFound(new { message = $"Product with ID {id} not found." });
        }

        return Ok(product);
    }

    /// <summary>
    /// Creates a new product.
    /// </summary>
    [HttpPost]
    [ProducesResponseType(typeof(ProductDto), StatusCodes.Status201Created)]
    [ProducesResponseType(StatusCodes.Status400BadRequest)]
    public async Task<IActionResult> Create([FromBody] CreateProductDto dto)
    {
        // Validation is automatic via FluentValidation
        var product = await _productService.CreateAsync(dto);

        // Returns 201 with the created resource URL
        return CreatedAtAction(
            nameof(GetById),
            new { id = product.Id },
            product);
    }

    /// <summary>
    /// Updates an existing product.
    /// </summary>
    [HttpPut("{id:int}")]
    [ProducesResponseType(typeof(ProductDto), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    [ProducesResponseType(StatusCodes.Status400BadRequest)]
    public async Task<IActionResult> Update(int id, [FromBody] UpdateProductDto dto)
    {
        var product = await _productService.UpdateAsync(id, dto);

        if (product == null)
        {
            return NotFound(new { message = $"Product with ID {id} not found." });
        }

        return Ok(product);
    }

    /// <summary>
    /// Deletes a product.
    /// </summary>
    [HttpDelete("{id:int}")]
    [ProducesResponseType(StatusCodes.Status204NoContent)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<IActionResult> Delete(int id)
    {
        var deleted = await _productService.DeleteAsync(id);

        if (!deleted)
        {
            return NotFound(new { message = $"Product with ID {id} not found." });
        }

        // 204 No Content for successful deletion
        return NoContent();
    }
}
```

De `ProducesResponseType`-attributen documenteren mogelijke responscodes voor automatische Swagger-documentatiegeneratie.

```csharp
// DTOs/PaginatedResponse.cs
namespace ProductApi.DTOs;

public class PaginatedResponse<T>
{
    public IEnumerable<T> Items { get; set; } = Enumerable.Empty<T>();
    public int Page { get; set; }
    public int PageSize { get; set; }
    public int TotalCount { get; set; }
    public int TotalPages { get; set; }
    public bool HasPreviousPage => Page > 1;
    public bool HasNextPage => Page < TotalPages;
}
```

> **Route Constraints**
>
> Het gebruik van constraints zoals `{id:int}` voorkomt routing-conflicten en retourneert automatisch een 404 als het formaat niet klopt.

## Globale Foutafhandeling

Een foutafhandelingsmiddleware centraliseert de verwerking van uitzonderingen voor consistente en veilige responses.

```csharp
// Middleware/ExceptionMiddleware.cs
using System.Net;
using System.Text.Json;

namespace ProductApi.Middleware;

public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<ExceptionMiddleware> _logger;
    private readonly IHostEnvironment _env;

    public ExceptionMiddleware(
        RequestDelegate next,
        ILogger<ExceptionMiddleware> logger,
        IHostEnvironment env)
    {
        _next = next;
        _logger = logger;
        _env = env;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            // Continue pipeline
            await _next(context);
        }
        catch (Exception ex)
        {
            // Log the error
            _logger.LogError(ex, "An unhandled exception occurred");

            // Prepare response
            context.Response.ContentType = "application/json";
            context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

            // Different response based on environment
            var response = _env.IsDevelopment()
                ? new ErrorResponse(
                    StatusCode: context.Response.StatusCode,
                    Message: ex.Message,
                    Details: ex.StackTrace)
                : new ErrorResponse(
                    StatusCode: context.Response.StatusCode,
                    Message: "An internal error occurred.",
                    Details: null);

            // Serialize with camelCase options
            var options = new JsonSerializerOptions
            {
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase
            };

            var json = JsonSerializer.Serialize(response, options);
            await context.Response.WriteAsync(json);
        }
    }
}

// DTO for error responses
public record ErrorResponse(int StatusCode, string Message, string? Details);

// Extension to register middleware
public static class ExceptionMiddlewareExtensions
{
    public static IApplicationBuilder UseExceptionMiddleware(this IApplicationBuilder app)
    {
        return app.UseMiddleware<ExceptionMiddleware>();
    }
}
```

```csharp
// Program.cs (adding middleware)
var app = builder.Build();

// Exception middleware must be first
app.UseExceptionMiddleware();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}
// ... rest of configuration
```

## Configuratie en Omgevingsvariabelen

Geexternaliseerde configuratie maakt het mogelijk de applicatie aan te passen aan verschillende omgevingen zonder codewijzigingen.

```json
// appsettings.json
{
  "ConnectionStrings": {
    "DefaultConnection": "Server=localhost;Database=ProductDb;User Id=sa;Password=YourPassword;TrustServerCertificate=true"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "Microsoft.EntityFrameworkCore": "Warning"
    }
  },
  "ApiSettings": {
    "DefaultPageSize": 10,
    "MaxPageSize": 100,
    "ApiVersion": "1.0"
  }
}
```

```csharp
// Configuration/ApiSettings.cs
namespace ProductApi.Configuration;

public class ApiSettings
{
    public int DefaultPageSize { get; set; } = 10;
    public int MaxPageSize { get; set; } = 100;
    public string ApiVersion { get; set; } = "1.0";
}
```

```csharp
// Program.cs (injecting configuration)
builder.Services.Configure<ApiSettings>(
    builder.Configuration.GetSection("ApiSettings"));

// Usage in a service
public class ProductService : IProductService
{
    private readonly ApiSettings _settings;

    public ProductService(IOptions<ApiSettings> settings)
    {
        _settings = settings.Value;
    }
}
```

## Unit Tests met xUnit

Unit tests valideren het gedrag van services en controllers in isolatie.

```csharp
// Tests/ProductServiceTests.cs
using Microsoft.EntityFrameworkCore;
using ProductApi.Data;
using ProductApi.DTOs;
using ProductApi.Models;
using ProductApi.Services;
using Xunit;

namespace ProductApi.Tests;

public class ProductServiceTests
{
    private AppDbContext CreateInMemoryContext()
    {
        // Configure in-memory database
        var options = new DbContextOptionsBuilder<AppDbContext>()
            .UseInMemoryDatabase(databaseName: Guid.NewGuid().ToString())
            .Options;

        return new AppDbContext(options);
    }

    [Fact]
    public async Task CreateAsync_ValidDto_ReturnsProductDto()
    {
        // Arrange
        using var context = CreateInMemoryContext();

        // Add test category
        var category = new Category { Id = 1, Name = "Electronics", Slug = "electronics" };
        context.Categories.Add(category);
        await context.SaveChangesAsync();

        var service = new ProductService(context);
        var dto = new CreateProductDto(
            Name: "Test Product",
            Description: "Test Description",
            Price: 99.99m,
            StockQuantity: 10,
            CategoryId: 1);

        // Act
        var result = await service.CreateAsync(dto);

        // Assert
        Assert.NotNull(result);
        Assert.Equal("Test Product", result.Name);
        Assert.Equal(99.99m, result.Price);
        Assert.Equal("Electronics", result.CategoryName);
    }

    [Fact]
    public async Task GetByIdAsync_NonExistent_ReturnsNull()
    {
        // Arrange
        using var context = CreateInMemoryContext();
        var service = new ProductService(context);

        // Act
        var result = await service.GetByIdAsync(999);

        // Assert
        Assert.Null(result);
    }

    [Fact]
    public async Task UpdateAsync_ExistingProduct_UpdatesFields()
    {
        // Arrange
        using var context = CreateInMemoryContext();

        var category = new Category { Id = 1, Name = "Tech", Slug = "tech" };
        var product = new Product
        {
            Id = 1,
            Name = "Original Name",
            Description = "Original Description",
            Price = 50.00m,
            StockQuantity = 5,
            CategoryId = 1
        };

        context.Categories.Add(category);
        context.Products.Add(product);
        await context.SaveChangesAsync();

        var service = new ProductService(context);
        var updateDto = new UpdateProductDto(
            Name: "Updated Name",
            Description: null,
            Price: 75.00m,
            StockQuantity: null,
            IsActive: null);

        // Act
        var result = await service.UpdateAsync(1, updateDto);

        // Assert
        Assert.NotNull(result);
        Assert.Equal("Updated Name", result.Name);
        Assert.Equal(75.00m, result.Price);
        // Fields not provided remain unchanged
        Assert.Equal(5, result.StockQuantity);
    }

    [Fact]
    public async Task DeleteAsync_ExistingProduct_ReturnsTrue()
    {
        // Arrange
        using var context = CreateInMemoryContext();

        var category = new Category { Id = 1, Name = "Test", Slug = "test" };
        var product = new Product
        {
            Id = 1,
            Name = "To Delete",
            Description = "Will be deleted",
            Price = 10.00m,
            CategoryId = 1
        };

        context.Categories.Add(category);
        context.Products.Add(product);
        await context.SaveChangesAsync();

        var service = new ProductService(context);

        // Act
        var result = await service.DeleteAsync(1);

        // Assert
        Assert.True(result);
        Assert.Null(await context.Products.FindAsync(1));
    }

    [Fact]
    public async Task GetAllAsync_WithSearch_FiltersResults()
    {
        // Arrange
        using var context = CreateInMemoryContext();

        var category = new Category { Id = 1, Name = "Category", Slug = "category" };
        context.Categories.Add(category);

        context.Products.AddRange(
            new Product { Id = 1, Name = "Apple iPhone", Description = "Phone", Price = 999, CategoryId = 1 },
            new Product { Id = 2, Name = "Samsung Galaxy", Description = "Phone", Price = 899, CategoryId = 1 },
            new Product { Id = 3, Name = "Apple MacBook", Description = "Laptop", Price = 1999, CategoryId = 1 }
        );
        await context.SaveChangesAsync();

        var service = new ProductService(context);

        // Act
        var (items, totalCount) = await service.GetAllAsync(search: "Apple");

        // Assert
        Assert.Equal(2, totalCount);
        Assert.All(items, p => Assert.Contains("Apple", p.Name));
    }
}
```

Tests worden uitgevoerd met `dotnet test` vanuit de projectroot.

## Conclusie

.NET 8 met ASP.NET Core biedt een compleet en performant ecosysteem voor het bouwen van professionele REST API's. De combinatie van Entity Framework Core voor datatoegang, FluentValidation voor validatie en native dependency injection maakt het mogelijk onderhoudbare en testbare applicaties te bouwen.

### Checklist voor een Kwalitatieve .NET API

- DTO's scheiden van domeinmodellen
- Servicelaag voor bedrijfslogica implementeren
- FluentValidation voor declaratieve validaties gebruiken
- Globale foutafhandelingsmiddleware configureren
- Configuratie externaliseren met IOptions
- Unit tests voor services schrijven
- API documenteren met Swagger/OpenAPI

De gelaagde architectuur (Controllers, Services, Repository/DbContext) bevordert de scheiding van verantwoordelijkheden en vergemakkelijkt de doorontwikkeling van de applicatie. .NET 8-functies zoals records, required properties en ExecuteDeleteAsync moderniseren de code en verbeteren tegelijkertijd de performance.

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Source: SharpSkill (https://sharpskill.dev), tech interview preparation for your real stack.
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