Pipeline Behaviors

Pipeline Behaviors, MediatR pipeline’ında request’lerin işlenmesi sırasında çalışan middleware’lerdir. Cross-cutting concern’ler için idealdir.

Behavior Özellikleri

1. Pre-Processing: Request handler’dan önce çalışır
2. Post-Processing: Request handler’dan sonra çalışır
3. Exception Handling: Exception’ları yakalayabilir
4. Response Manipulation: Response’ları değiştirebilir

Yaygın Behavior Örnekleri

Logging Behavior

public class LoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    private readonly ILogger<LoggingBehavior<TRequest, TResponse>> _logger;

    public LoggingBehavior(ILogger<LoggingBehavior<TRequest, TResponse>> logger)
    {
        _logger = logger;
    }

    public async Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        _logger.LogInformation("Handling {RequestName}", typeof(TRequest).Name);

        var response = await next();

        _logger.LogInformation("Handled {RequestName}", typeof(TRequest).Name);

        return response;
    }
}

Validation Behavior

public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    private readonly IEnumerable<IValidator<TRequest>> _validators;

    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
    {
        _validators = validators;
    }

    public async Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        var context = new ValidationContext<TRequest>(request);

        var failures = _validators
            .Select(v => v.Validate(context))
            .SelectMany(result => result.Errors)
            .Where(f => f != null)
            .ToList();

        if (failures.Any())
        {
            throw new ValidationException(failures);
        }

        return await next();
    }
}

Transaction Behavior

public class TransactionBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    private readonly IUnitOfWork _unitOfWork;

    public TransactionBehavior(IUnitOfWork unitOfWork)
    {
        _unitOfWork = unitOfWork;
    }

    public async Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        await _unitOfWork.BeginTransactionAsync();

        try
        {
            var response = await next();
            await _unitOfWork.CommitTransactionAsync();
            return response;
        }
        catch
        {
            await _unitOfWork.RollbackTransactionAsync();
            throw;
        }
    }
}

Performance Behavior

public class PerformanceBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    private readonly ILogger<PerformanceBehavior<TRequest, TResponse>> _logger;
    private readonly Stopwatch _timer;

    public PerformanceBehavior(ILogger<PerformanceBehavior<TRequest, TResponse>> logger)
    {
        _logger = logger;
        _timer = new Stopwatch();
    }

    public async Task<TResponse> Handle(
        TRequest request,
        RequestHandlerDelegate<TResponse> next,
        CancellationToken cancellationToken)
    {
        _timer.Start();

        var response = await next();

        _timer.Stop();

        var elapsedMilliseconds = _timer.ElapsedMilliseconds;

        if (elapsedMilliseconds > 500)
        {
            _logger.LogWarning(
                "Long Running Request: {RequestName} ({ElapsedMilliseconds} milliseconds)",
                typeof(TRequest).Name,
                elapsedMilliseconds);
        }

        return response;
    }
}

Behavior Best Practices

1. Behavior Sıralaması - Validation - Authorization - Logging - Transaction - Caching - Performance

2. Error Handling - Her behavior kendi exception’larını yakalamalı - Global exception handling kullanılmalı

3. Testing - Behavior’lar unit test edilmeli - Integration testler yazılmalı

4. Performance - Behavior’lar hafif olmalı - Gereksiz işlemlerden kaçınılmalı

Behavior Registration

services.AddMediatR(cfg => {
    cfg.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly());
    cfg.AddBehavior(typeof(ValidationBehavior<,>));
    cfg.AddBehavior(typeof(LoggingBehavior<,>));
    cfg.AddBehavior(typeof(TransactionBehavior<,>));
    cfg.AddBehavior(typeof(PerformanceBehavior<,>));
});