无法向 Mediatr 注册 IRequestPreProcessors

Question

我想注册以下虚拟 IRequestPreProcessor (Mediator 3)

public class IdentifyUserTypeCommandHandler : IRequestPreProcessor<RegisterUserCommand>
{
    private readonly IOptions<TecApiOptions> _options;

    public IdentifyUserTypeCommandHandler(IOptions<TecApiOptions> options)
    {
        _options = options;
    }

    public async Task Process(RegisterUserCommand request)
    {
        request.Type = "internal";
        await Task.FromResult(true);
    }
}

为此，我设置了容器以将 IRequestPreProcessor 映射到我的具体实现 IdentifyUserTypeCommandHandler

        // Pipeline engine used internally to simplify controllers
        services.AddMediatR();
        // Pre-processors
        services.AddTransient(typeof(IRequestPreProcessor<RegisterUserCommand>), typeof(IdentifyUserTypeCommandHandler));

        // Registers command validator
        services.AddTransient(typeof(IValidator<RegisterUserCommand>), typeof(RegisterUserCommandValidator));

        // Registers generic behaviors
        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(Pipeline<,>));
        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(LoggingBehavior<,>));
        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehavior<,>));
        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestPreProcessorBehavior<,>));

一旦我运行代码，我就会得到以下异常

System.ArgumentException: Open generic service type 'MediatR.Pipeline.IRequestPreProcessor`1[TRequest]' requires registering an open generic implementation type.

我想运行此预处理器仅用于 RegisterUserCommand 类型的命令。知道如何解决这个问题吗？

仅供参考，

public class LoggingBehavior<TCommand, TResponse> : IPipelineBehavior<TCommand, TResponse>
{
    private readonly ILogger _logger;

    public LoggingBehavior(ILoggerFactory loggerFactory)
    {
        _logger = loggerFactory?.CreateLogger(typeof(TCommand).Name) ?? throw new ArgumentNullException(nameof(loggerFactory));
    }

    public async Task<TResponse> Handle(TCommand request, RequestHandlerDelegate<TResponse> next)
    {
        try
        {
            _logger.LogInformation(LoggingEvents.RUN_HANDLER, $"Handling '{typeof(TCommand).Name}'");
            var response = await next();
            _logger.LogInformation(LoggingEvents.RUN_HANDLER, $"Handled '{typeof(TResponse).Name}'");
            return response;
        }
        catch (Exception e)
        {
            _logger.LogError(
                LoggingEvents.RUN_HANDLER_EXCEPTION, e,
                $"An error occured while processing pipeline '{GetType().Name}' [{typeof(TCommand).Name} >> {typeof(TResponse).Name}]");
            throw;
        }
    }
}

谢谢，问候，塞布

Answer 1

所以在与 lib 的创建者交谈后，似乎 Pre & Post 处理器必须有一个通用定义。

public class GenericRequestPostProcessor<TRequest, TResponse> : IRequestPostProcessor<TRequest, TResponse>

或

public class GenericRequestPreProcessor<TRequest> : IRequestPreProcessor<TRequest>

来源：Examples

创建新的 Pre/Post 处理器时需要 <TRequest> 和 <TRequest, TResponse>。现在我稍后会尝试回答 1 000 000 美元的问题：

How do we specialize processors so they deal with a specific set of requests/commands (without having to check request type)...

Answer 2

如果您正在使用 services.AddMediatR()

确保注册内置行为：RequestPreProcessorBehavior

services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestPreProcessorBehavior<,>));
services.AddMediatR();

然后你的预处理器需要根据@Sebastien的回答有通用定义：

public class PingDecorator<TRequest> : IRequestPreProcessor<TRequest>
{
    public Task Process(TRequest request)
    {
        return Unit.Task;
    }
}

如果您希望预处理器仅用于特定请求：

public class PingDecorator<TRequest> : IRequestPreProcessor<TRequest> where TRequest:Ping
{
    public Task Process(TRequest request)
    {
        request.Message = request.Message + " Decorated";
        return Unit.Task;
    }
}

Answer 3

最新版本内置注册，使用从程序集检索，无需注册。请注意，我已经使用多个 IRequestPreProcessor 实现对其进行了测试，并且所有这些实现都按照它们在代码中编写的相同顺序工作。我认为这可能是一个语义错误，因为从逻辑上讲它不应该只有一个 RequestPreProcessor。

无法向 Mediatr 注册 IRequestPreProcessors

Unable to register IRequestPreProcessors with Mediatr

dependency-injection

asp.net-core

mediatr