Command Pattern

Command Pattern, veri değiştirme işlemlerini temsil eden bir pattern’dır. MediatR’da command’lar IRequest<T> interface’ini implemente eder.

Command Özellikleri

1. Immutable: Command’lar immutable olmalıdır
2. Tek Sorumluluk: Her command tek bir iş yapmalıdır
3. Validation: Command’lar validate edilebilir olmalıdır
4. Idempotent: Mümkünse idempotent olmalıdır

Command Örnekleri

Basit Command

public class CreateProductCommand : IRequest<int>
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

public class CreateProductCommandHandler : IRequestHandler<CreateProductCommand, int>
{
    private readonly IProductRepository _repository;

    public CreateProductCommandHandler(IProductRepository repository)
    {
        _repository = repository;
    }

    public async Task<int> Handle(CreateProductCommand request, CancellationToken cancellationToken)
    {
        var product = new Product
        {
            Name = request.Name,
            Price = request.Price
        };

        await _repository.AddAsync(product);
        return product.Id;
    }
}

Complex Command

public class UpdateProductCommand : IRequest
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    public string Description { get; set; }
}

public class UpdateProductCommandHandler : IRequestHandler<UpdateProductCommand>
{
    private readonly IProductRepository _repository;
    private readonly IUnitOfWork _unitOfWork;

    public UpdateProductCommandHandler(
        IProductRepository repository,
        IUnitOfWork unitOfWork)
    {
        _repository = repository;
        _unitOfWork = unitOfWork;
    }

    public async Task<Unit> Handle(UpdateProductCommand request, CancellationToken cancellationToken)
    {
        var product = await _repository.GetByIdAsync(request.Id);

        product.Name = request.Name;
        product.Price = request.Price;
        product.Description = request.Description;

        await _repository.UpdateAsync(product);
        await _unitOfWork.SaveChangesAsync();

        return Unit.Value;
    }
}

Command Best Practices

1. Command Validation - FluentValidation kullanın - Validation logic’i behavior’larda olmalı

2. Command Handler Organization - Her handler tek bir repository kullanmalı - Business logic handler içinde olmalı - Cross-cutting concern’ler behavior’lara taşınmalı

3. Error Handling - Özel exception tipleri kullanın - Global exception handling kullanın

4. Testing - Handler’lar unit test edilmeli - Integration testler yazılmalı

Command Pipeline

Command’lar pipeline üzerinden geçer:

1. Validation
2. Authorization
3. Logging
4. Transaction
5. Handler
6. Event Publishing

public class CommandPipelineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    public async Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        // Pre-processing
        var response = await next();
        // Post-processing
        return response;
    }
}