如何在 Mediatr 中为所有请求定义一个特定的异常处理程序

Question

我在 ASP.NET core 项目中使用 Mediatr 来处理所有请求。我实现了几个请求/响应/处理程序。它们中的每一个都可以抛出一个特定的异常，我们将其称为“MyException”类。我将异常处理程序定义为

    public class MyExceptionHandler : RequestExceptionHandler<MyRequest<MyResponse>, MyResponse, MyException>
    {
        protected override void Handle(MyRequest<MyResponse> request, MyException exception, RequestExceptionHandlerState<MyResponse> state)
        {
            MyResponse response = new MyResponse();
            //Set some specific properties here in the response to indicate an error occurred
            state.SetHandled(response);
        }
    }

我将此异常处理程序添加到 (Autofac) 依赖项容器中，如果我在 MyRequest 和 MyResponse 的 MyHandler 中抛出 MyException，则该异常处理程序有效。但是，我有数十个请求、响应和相应的处理程序。那么我如何为所有这些异常注册这个特定异常的异常处理程序（注意：所有响应都派生自同一个基类）。它尝试了类似下面的内容，但是，没有被调用。它仅在我给出实际类型时才有效，但这意味着我必须为每种类型创建一个异常处理程序，这远远不切合实际。关于如何解决这个问题有什么想法吗？

    public class MyExceptionHandler : RequestExceptionHandler<IRequest<BaseResponse>, BaseResponse, MyException>
    {
        protected override void Handle(IRequest<BaseResponse> request, MyException exception, RequestExceptionHandlerState<BaseResponse> state)
        {
            BaseResponse response = new BaseResponse();
            //Set some specific properties here in the response to indicate an error occurred
            state.SetHandled(response);
        }
    }

Answer 1

您可以像这样创建一个通用的：

public class ExceptionLoggingHandler<TRequest, TResponse, TException> : IRequestExceptionHandler<TRequest, TResponse, TException>
         where TRequest : IRequest<TResponse>
         where TException : Exception
    {
        private readonly ILogger<ExceptionLoggingHandler<TRequest, TResponse, TException>> _logger;

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

        public Task Handle(TRequest request, TException exception, RequestExceptionHandlerState<TResponse> state, CancellationToken cancellationToken)
        {
            _logger.LogError(exception, "Something went wrong while handling request of type {@requestType}", typeof(TRequest));

            // TODO: when we want to show the user somethig went wrong, we need to expand this with something like
            // a ResponseBase where we wrap the actual response and return an indication whether the call was successful or not.
            state.SetHandled(default!);

            return Task.CompletedTask;
        }
    }

然后在 IerviceC 上像这样注册它：

services.AddTransient(typeof(IRequestExceptionHandler<,,>), typeof(ExceptionLoggingHandler<,,>));

因为该类RequestExceptionProcessorBehavior将寻找具有 3 个泛型的类型，而不是一个IRequestExceptionHandler<,>。