使用 MediatR 是否可以为任何和所有请求创建通用的 RequestExceptionHandler？

Question

我创建了一个具有如下已知类型的请求异常处理程序，并处理了异常。我发现的唯一例子就是这样做的。

using MediatR.Pipeline;
using Microsoft.Extensions.Logging;
using MyPortal.Application.Common.Models;
using MyPortal.Application.MyCommands.Commands.CompleteMyCommand;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace MyPortal.Application.Common.Behaviors
{
    public class RequestGenericExceptionHandler : IRequestExceptionHandler<MyCommand, Result>
    {
        private readonly ILogger<MyCommand> _logger;

        public RequestGenericExceptionHandler(ILogger<MyCommand> logger)
        {
            _logger = logger;
        }

        public async Task Handle(MyCommand request,
            Exception exception,
            RequestExceptionHandlerState<Result> state,
            CancellationToken cancellationToken)
        {
            var name = typeof(MyCommand).Name;
            _logger.LogError("MyPortal Request Exception {@Request}",
                    name, exception.Message, request);
        }
    }
}

当我尝试使用这样的东西时，它没有被处理：

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

        public RequestGenericExceptionHandler(ILogger<TRequest> logger)
        {
            _logger = logger;
        }

        public async Task Handle(TRequest request,
            Exception exception,
            RequestExceptionHandlerState<TResponse> state,
            CancellationToken cancellationToken)
        {
            var name = typeof(TRequest).Name;
            _logger.LogError("MyPortal Request Exception {@Request}",
                    name, exception.Message, request);
        }
    }

我正在使用 .Net Core 3.1、Mediator 8.0.1 和 MediatR.Extensions.Microsoft.DependencyIntjection 8.0.0，这是我唯一的依赖注入：

            services.AddMediatR(Assembly.GetExecutingAssembly());

Answer 1

我需要做出这些改变：

public class RequestGenericExceptionHandler<TRequest, TResponse, TException> : IRequestExceptionHandler<TRequest, TResponse, TException>
    where TException : Exception {

    public async Task Handle(TRequest request,
        TException exception,
        RequestExceptionHandlerState<TResponse> state,
        CancellationToken cancellationToken) {}
}

仅在不使用时才需要此行

MediatR.Extensions.Microsoft.DependencyIntjection

：

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

参考：https://github.com/jbogard/MediatR/issues/486

Answer 2

这样的事情应该有效。此外，如果您想返回异常的通用响应，您可以让所有响应类实现相同的接口，然后返回一个通用的接口

public class GenericRequestExceptionHandler<TRequest, TResponse, TException> : IRequestExceptionHandler<TRequest, TResponse, TException>
    where TRequest : IRequest
    where TResponse : Result
    where TException : Exception
{
    private readonly ILogger<TRequest> _logger;
    public GenericRequestExceptionHandler(ILogger<TRequest> logger)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }
    public async Task Handle(TRequest request, TException exception, RequestExceptionHandlerState<TResponse> state, CancellationToken cancellationToken = new CancellationToken())
    {
        _logger.LogError(exception, $"Error occurs on handling {nameof(TRequest)}");
        await Task.Run(() => state.SetHandled((TResponse)Result.Failure(new string[] { exception.Message })));
    }
}