[注意：这是一个“替换”问题。第一个是基于我的主要项目的代码，所以我用来自单一用途项目的代码重做了这个问题，更清楚地说明了原理。问题保持不变，只是更好地提出。]
情景
我正在尝试使用 MediatR 管道行为和 Autofac 在 CQRS 请求管道上设置命令预处理器以进行请求路由。我的目标是让预处理器只为命令 (ICommand<>) 而不是所有请求 (IRequest<>) 运行，这将导致预处理器执行命令、查询和事件。
问题
我可以让我的 GenericPreProcessor 或任何其他预处理器对所有类型的请求运行良好，但是我用来尝试“过滤”注入的任何方法要么返回错误，要么根本不执行所需的预处理器.
我在 Autofac 中为所有请求工作的管道配置如下所示：
// Pipeline pre/post processors
builder
.RegisterGeneric(typeof(RequestPostProcessorBehavior<,>))
.As(typeof(IPipelineBehavior<,>));
builder
.RegisterGeneric(typeof(RequestPreProcessorBehavior<,>))
.As(typeof(IPipelineBehavior<,>));
// Works as desired: Fires generic pre-processor for ALL requests, both cmd and query
builder
.RegisterGeneric(typeof(GenericRequestPreProcessor<>))
.As(typeof(IRequestPreProcessor<>));
// Works for all requests, but I need a way to limit it to commands
builder
.RegisterGeneric(typeof(MyCommandPreProcessor<>))
.As(typeof(IRequestPreProcessor<>));
从概念上讲，我正在尝试做任何类似的事情，但失败了：
builder
.RegisterGeneric(typeof(MyCommandPreProcessor<>)) // Note generic
.As(typeof(IRequestPreProcessor<ICommand<>>));
// Intellisense error "Unexpected use of an unbound generic"
builder
.RegisterType(typeof(MyCommandPreProcessor)) // Note non-generic
.As(typeof(IRequestPreProcessor<ICommand<>>));
// Intellisense error "Unexpected use of an unbound generic"
builder
.RegisterType(typeof(MyCommandPreProcessor)) // Note non-generic
.As(typeof(IRequestPreProcessor<ICommand<CommonResult>>));
// No errors, but MyCommandPreProcessor not firing
我正在为 MyCommandPreProcessor 尝试几种不同的配置，一个通用的和一个非通用的，但我被以下任何一个难住了：
public class MyCommandPreProcessor<TRequest> : IRequestPreProcessor<TRequest>
{
public Task Process(TRequest request, CancellationToken cancellationToken)
{
Debug.WriteLine("***** MYCOMMAND PREPROCESSOR CALLED *****");
return Task.CompletedTask;
}
}
- OR -
public class MyCommandPreProcessor : IRequestPreProcessor<IRequest<ICommonResponse>>
{
public Task Process(TRequest request, CancellationToken cancellationToken)
{
Debug.WriteLine("***** MYCOMMAND PREPROCESSOR CALLED *****");
return Task.CompletedTask;
}
}
我的问题
关于如何注册一个预处理器的任何想法，该预处理器将被限制为仅针对 ICommand<> 的封闭类型的 IRequest<> 类型触发？
辅助材料
GitHub上的项目
整个最小示例项目可以在https://github.com/jhoiby/MediatRPreProcessorTest查看或克隆
Autofac MediatR 配置
一个工作配置，所有请求都有一个 GenericRequestPreProcessor。
builder.RegisterAssemblyTypes(typeof(IMediator).GetTypeInfo().Assembly).AsImplementedInterfaces();
var mediatrOpenTypes = new[]
{
typeof(IRequestHandler<,>),
typeof(IRequestHandler<>),
typeof(INotificationHandler<>)
};
foreach (var mediatrOpenType in mediatrOpenTypes)
{
// Register all command handler in the same assembly as WriteLogMessageCommandHandler
builder
.RegisterAssemblyTypes(typeof(MyCommandHandler).GetTypeInfo().Assembly)
.AsClosedTypesOf(mediatrOpenType)
.AsImplementedInterfaces();
// Register all QueryHandlers in the same assembly as GetExternalLoginQueryHandler
builder
.RegisterAssemblyTypes(typeof(MyQueryHandler).GetTypeInfo().Assembly)
.AsClosedTypesOf(mediatrOpenType)
.AsImplementedInterfaces();
}
// Pipeline pre/post processors
builder.RegisterGeneric(typeof(RequestPostProcessorBehavior<,>)).As(typeof(IPipelineBehavior<,>));
builder.RegisterGeneric(typeof(RequestPreProcessorBehavior<,>)).As(typeof(IPipelineBehavior<,>));
builder.RegisterGeneric(typeof(GenericRequestPreProcessor<>)).As(typeof(IRequestPreProcessor<>));
// builder.RegisterGeneric(typeof(GenericRequestPostProcessor<,>)).As(typeof(IRequestPostProcessor<,>));
// builder.RegisterGeneric(typeof(GenericPipelineBehavior<,>)).As(typeof(IPipelineBehavior<,>));
builder.Register<SingleInstanceFactory>(ctx =>
{
var c = ctx.Resolve<IComponentContext>();
return t => c.Resolve(t);
});
builder.Register<MultiInstanceFactory>(ctx =>
{
var c = ctx.Resolve<IComponentContext>();
return t => (IEnumerable<object>)c.Resolve(typeof(IEnumerable<>).MakeGenericType(t));
});
MyCommandPreProcessor 类
我正在试验这两种，通用的和非通用的：
public class MyCommandPreProcessor<TRequest> : IRequestPreProcessor<TRequest>
{
public Task Process(TRequest request, CancellationToken cancellationToken)
{
Debug.WriteLine("***** MYCOMMAND PREPROCESSOR CALLED *****");
return Task.CompletedTask;
}
}
- AND -
public class MyCommandPreProcessor : IRequestPreProcessor<IRequest<ICommonResponse>>
{
public Task Process(TRequest request, CancellationToken cancellationToken)
{
Debug.WriteLine("***** MYCOMMAND PREPROCESSOR CALLED *****");
return Task.CompletedTask;
}
}
继承结构
// Requests
IMediatR.IRequest<TResponse>
<- IMessage<TResponse>
<- ICommand<TResponse>
<- concrete MyCommand : ICommand<CommonResponse>
<- IQuery<TResponse>
<- concrete MyQuery : IQuery<CommonResponse>
// Request Handlers
IMediatR.IRequestHandler<in TRequest,TResponse>
<- IMessageHandler<in TRequest,TResponse>
<- ICommandHandler<in TRequest,TResponse>
<- concrete MyCommandHandler : ICommandHandler<MyCommand,CommonResponse>
<- IQueryHandler<In TRequest,TResponse>
<- concrete MyQueryHandler : IQueryHandler<MyQuery,CommonResponse>
// CommonResponse - A POCO that returns result info
ICommonResponse
<- concrete CommonResponse
命令
public interface IMessage<TResponse> : MediatR.IRequest<TResponse>
{
}
public interface ICommand<TResponse> : IMessage<TResponse>
{
}
public class MyCommand : ICommand<CommonResponse>
{
}
命令处理程序
public interface IMessageHandler<in TRequest, TResponse>
: MediatR.IRequestHandler<TRequest, TResponse>
where TRequest : IRequest<TResponse>
{
}
public interface ICommandHandler<in TRequest, TResponse>
: IMessageHandler<TRequest, TResponse>
where TRequest : IRequest<TResponse>
{
}
public class MyCommandHandler : ICommandHandler<MyCommand, CommonResponse>
{
public async Task<CommonResponse> Handle(
MyCommand request,
CancellationToken cancellationToken)
{
Debug.WriteLine(" ***** Command handler executing *****");
return
new CommonResponse(
succeeded: true,
data: "Command execution completed successfully.");
}
}
预处理器注入目标（在 MediatR 管道代码中）
接收注入的 IRequestPreProcessor<> 的构造函数是：
public RequestPreProcessorBehavior(IEnumerable<IRequestPreProcessor<TRequest>> preProcessors)
{
...
}
可以在 Github 上文件的第 17 行看到：
https://github.com/jbogard/MediatR/blob/master/src/MediatR/Pipeline/RequestPreProcessorBehavior.cs
谢谢！