.NET Core 7 Minimal API中MediatR请求处理器映射失败求助

错误信息 #

Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
      System.InvalidOperationException: Error constructing handler for request of type MediatR.IRequestHandler`2[mNet.FileServer.Commands.Core.Application.Features.StoredFileTypes.NewStoredFileType.NewStoredFileTypeCommand,mNet.Common.Core.Application.Commands.BaseCommandResponse`1[mNet.FileServer.Shared.Core.Domain.StoredFileTypes.ValueObjects.StoredFileTypeId]]. Register your handlers with the container. See the samples in GitHub for examples.
       ---> System.InvalidOperationException: No service for type 'MediatR.IRequestHandler`2[mNet.FileServer.Commands.Core.Application.Features.StoredFileTypes.NewStoredFileType.NewStoredFileTypeCommand,mNet.Common.Core.Application.Commands.BaseCommandResponse`1[mNet.FileServer.Shared.Core.Domain.StoredFileTypes.ValueObjects.StoredFileTypeId]]' has been registered.
         at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
         at MediatR.ServiceFactoryExtensions.GetInstance[T](ServiceFactory factory)
         at MediatR.Wrappers.HandlerBase.GetHandler[THandler](ServiceFactory factory)
         --- End of inner exception stack trace ---
         at MediatR.Wrappers.HandlerBase.GetHandler[THandler](ServiceFactory factory)
         at MediatR.Wrappers.RequestHandlerWrapperImpl`2.<>c__DisplayClass1_0.<Handle>g__Handler|0()
         at MediatR.Pipeline.RequestExceptionProcessorBehavior`2.Handle(TRequest request, RequestHandlerDelegate`1 next, CancellationToken cancellationToken)
         at MediatR.Pipeline.RequestExceptionProcessorBehavior`2.Handle(TRequest request, RequestHandlerDelegate`1 next, CancellationToken cancellationToken)
         at MediatR.Pipeline.RequestExceptionActionProcessorBehavior`2.Handle(TRequest request, RequestHandlerDelegate`1 next, CancellationToken cancellationToken)
         at MediatR.Pipeline.RequestExceptionActionProcessorBehavior`2.Handle(TRequest request, RequestHandlerDelegate`1 next, CancellationToken cancellationToken)
         at MediatR.Pipeline.RequestPostProcessorBehavior`2.Handle(TRequest request, RequestHandlerDelegate`1 next, CancellationToken cancellationToken)
         at MediatR.Pipeline.RequestPreProcessorBehavior`2.Handle(TRequest request, RequestHandlerDelegate`1 next, CancellationToken cancellationToken)
         at mNet.FileServer.Commands.Ui.MinimalApi.Endpoints.StoredFileTypeEndpoint.NewStoredFileTypeAsync(NewStoredFileTypeDto request, IMediator mediator) in C:\Users\dcmea\OneDrive\mNet Microservices\mNet.FileServer\mNet.FileServer.Commands.Ui.MinimalApi\Endpoints\StoredFileTypeEndpoint.cs:line 47
         at Microsoft.AspNetCore.Http.RequestDelegateFactory.<ExecuteTaskOfT>g__ExecuteAwaited|111_0[T](Task`1 task, HttpContext httpContext)
         at Microsoft.AspNetCore.Http.RequestDelegateFactory.<>c__DisplayClass89_2.<<HandleRequestBodyAndCompileRequestDelegateForJson>b__2>d.MoveNext()
      --- End of stack trace from previous location ---
         at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
         at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
         at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
         at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

项目结构 #

• mNet.Common.Core.Application: 包含BaseCommand和BaseCommandResponse类
• mNet.FileServer.Shared.Core.Domain: 包含StoredFileTypeId值对象
• mNet.FileServer.Commands.Core.Domain: 包含StoredFileType聚合根
• mNet.FileServer.Commands.Core.Application: 包含NewStoredFileTypeCommand和NewStoredFileTypeCommandHandler类
• mNet.FileServer.Commands.Ui.MinimalApi: 包含主Program.cs和Minimal API端点

关键代码片段 #

Program.cs（片段） #

builder.Services.AddMediatR(AppDomain.CurrentDomain.GetAssemblies());

Minimal API端点方法 #

private static async Task<BaseCommandResponse<StoredFileTypeId>> NewStoredFileTypeAsync(NewStoredFileTypeDto request, IMediator mediator)
{
    var messageId = Guid.NewGuid();
    var command = new NewStoredFileTypeCommand
    {
        Id = new MessageId(messageId),
        CorrelationId = new CorrelationId(messageId),
        CausationId = new CausationId(messageId),
        CommandDto = request
    };

    var response = await mediator.Send(command); // 错误发生在此行，对应日志第47行
    return response;
}

NewStoredFileTypeCommand类 #

public class NewStoredFileTypeCommand : BaseCommand, IRequest<BaseCommandResponse<StoredFileTypeId>>
{
    public NewStoredFileTypeDto CommandDto { get; init; } = default!;
}

NewStoredFileTypeCommandHandler类 #

public class NewStoredFileTypeCommandHandler : IRequestHandler<NewStoredFileTypeCommand, BaseCommandResponse<StoredFileTypeId>>
{
    private readonly IMapper _mapper;
    private readonly IEventSourcingHandler<StoredFileType, StoredFileTypeId> _eventSourcingHandler;

    public NewStoredFileTypeCommandHandler(IMapper mapper,
        IEventSourcingHandler<StoredFileType, StoredFileTypeId> eventSourcingHandler)
    {
        _mapper = mapper;
        _eventSourcingHandler = eventSourcingHandler;
    }

    public async Task<BaseCommandResponse<StoredFileTypeId>> Handle(NewStoredFileTypeCommand request, CancellationToken cancellationToken)
    {
       var response = new BaseCommandResponse<StoredFileTypeId>();

        var aggregate = new StoredFileType(
            new StoredFileTypeId(Guid.NewGuid()), 
            request.CorrelationId, 
            new CausationId(request.Id.Id),
            request.CommandDto.Name, 
            request.CommandDto.IsImageFileType,
            _mapper.Map<BootstrapIconCode>(request.CommandDto.BootstrapIconCode),
            _mapper.Map<MimeType>(request.CommandDto.MimeType)
            );
        
        await _eventSourcingHandler.SaveAsync(aggregate);

        response.Id = aggregate.Id;
        response.Message = $"Created new {nameof(StoredFileType)} aggregate!";
        response.IsSuccessful = true;

        return response;
    }
}

问题说明 #

调试后确认MediatR未能将NewStoredFileTypeCommandHandler映射到对应的NewStoredFileTypeCommand，但已在Program.cs中配置了AppDomain.CurrentDomain.GetAssemblies()来扫描所有程序集，暂时无法定位原因，求排查思路。

内容的提问来源于stack exchange，提问作者dmeadley