c# - 如何在 Mediatr 中为所有请求定义一个特定的异常处理程序

Question

我将 Mediatr 用于 ASP.NET 核心项目来处理所有请求。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，我们称这个为“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，这将起作用。但是，我有几十个请求、响应和相应的处理程序。那么我如何为这个特定的异常注册这个异常处理程序呢(注意:所有的响应都来自同一个基类)。它尝试了类似下面的内容，但是没有被调用。它只有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，这远非实用。关于如何解决这个问题的任何想法？

    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

你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;
        }
    }

然后像这样在 IerviceC 上注册它:

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

因为 RequestExceptionProcessorBehavior类将使用 3 个泛型查找此类型，而不是 IRequestExceptionHandler<,>一个。