C#•4mo ago

✅ MediatR Pipeline where TResponse has a generic type

All my API methods return a Result wrapper, like so:

public class Result
{
    public bool IsSuccess { get; set; }
    public string Message { get; set; }
    public TimeSpan Time { get; set; }
    public Exception ResultException { get; set; }
}

public class Result<T> : Result
{
    public T Obj { get; set; }
}

public class Result
{
    public bool IsSuccess { get; set; }
    public string Message { get; set; }
    public TimeSpan Time { get; set; }
    public Exception ResultException { get; set; }
}

public class Result<T> : Result
{
    public T Obj { get; set; }
}

2 Replies

Camster•4mo ago

I want to use MediatR's pipeline to log exceptions to a separate database. But I'm not quite sure how to add a third generic type to the IPipelineBehavior. I tried this:

// Without response object
public class ExceptionPipeline<TRequest, TResponse> : IPipelineBehavior<TRequest, Result> 
{
    private IExceptionHandler _handler;

    public ExceptionPipeline(IExceptionHandler handler) 
    {
        _handler = handler;
    }

    public async Task<Result> Handle(TRequest request, RequestHandlerDelegate<Result> next, CancellationToken cancellationToken) 
    {
        Result response;
        try 
        {
            response = await next();
        } catch (Exception ex) 
        {
            var message = await _handler.LogException(ex);
            response = Result.Failure(message);
        }
        return response;
    }
}

// With response object
public class ExceptionPipeline<TRequest, TResponse, TResult> : IPipelineBehavior<TRequest, Result<TResult>> 
{
    private IExceptionHandler _handler;

    public ExceptionPipeline(IExceptionHandler handler) 
    {
        _handler = handler;
    }

    public async Task<Result<TResult>> Handle(TRequest request, RequestHandlerDelegate<Result<TResult>> next, CancellationToken cancellationToken) 
    {
        Result<TResult> response;
        try 
        {
            response = await next();
        } catch (Exception ex) 
        {
            var message = await _handler.LogException(ex);
            response = Result<TResult>.Failure(message);
        }
        return response;
    }
}

// Without response object
public class ExceptionPipeline<TRequest, TResponse> : IPipelineBehavior<TRequest, Result> 
{
    private IExceptionHandler _handler;

    public ExceptionPipeline(IExceptionHandler handler) 
    {
        _handler = handler;
    }

    public async Task<Result> Handle(TRequest request, RequestHandlerDelegate<Result> next, CancellationToken cancellationToken) 
    {
        Result response;
        try 
        {
            response = await next();
        } catch (Exception ex) 
        {
            var message = await _handler.LogException(ex);
            response = Result.Failure(message);
        }
        return response;
    }
}

// With response object
public class ExceptionPipeline<TRequest, TResponse, TResult> : IPipelineBehavior<TRequest, Result<TResult>> 
{
    private IExceptionHandler _handler;

    public ExceptionPipeline(IExceptionHandler handler) 
    {
        _handler = handler;
    }

    public async Task<Result<TResult>> Handle(TRequest request, RequestHandlerDelegate<Result<TResult>> next, CancellationToken cancellationToken) 
    {
        Result<TResult> response;
        try 
        {
            response = await next();
        } catch (Exception ex) 
        {
            var message = await _handler.LogException(ex);
            response = Result<TResult>.Failure(message);
        }
        return response;
    }
}

But I get an error that basically says the implementation Type can't be converted to the service type. Any help would be appreciated!

Camster•4mo ago

I found the solution here: https://github.com/jbogard/MediatR/issues/182

GitHub

Issue with Generic Wrapper as response type in pipeline · Issue #18...

When adding a Generic request result wrapper to all of my mediator request response types, the pipeline refuses to execute, throwing a generic type constraint exception that the request does not fi...

Gaming

Programming

✅ MediatR Pipeline where TResponse has a generic type