MediatR未在Autofac中注册：请求处理组件注册异常求助

异常详情 #

Autofac.Core.Registration.ComponentNotRegisteredException
HResult=0x80131500
Message=请求的服务'MediatR.IRequestHandler2[[MyApp.Features.Auth.SignIn.Requests.SignInRequest, MyApp.Application, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[MyApp.Features.Auth.SignIn.Response.SignInResponse, MyApp.Application, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]'尚未注册。要避免此异常，请注册提供该服务的组件、使用IsRegistered()检查注册情况，或使用ResolveOptional()解析可选依赖项。 Source=Autofac StackTrace: at Autofac.ResolutionExtensions.ResolveService(IComponentContext context, Service service, IEnumerable1 parameters)
at MyApp.Infrastructure.MediatorModules.MediatorModules.<>c__DisplayClass0_0.b__2(Type t) in E:\JJ\MyApp\MyApp.Infrastructure\MediatorModules\MediatorModules.cs:line 23
at MediatR.ServiceFactoryExtensions.GetInstance[T](ServiceFactory factory)
at MediatR.Wrappers.HandlerBase.GetHandler[THandler](ServiceFactory factory)

相关代码 #

MyMediatorModule类 #

public class MyMediatorModule : Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterType<Mediator>()
            .As<IMediator>()
            .InstancePerLifetimeScope();

        builder.Register<ServiceFactory>(context =>
        {
            var c = context.Resolve<IComponentContext>();
            return t => c.Resolve(t);
        });

        builder.RegisterAssemblyTypes(typeof(MyMediatorModule ).Assembly)
            .Where(t => t.Namespace.Contains("MyApp.Features"))
            .AsImplementedInterfaces();
    }
}

Startup配置 #

builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());
builder.Host.ConfigureContainer<ContainerBuilder>(builder =>
{
    builder.RegisterAssemblyModules(typeof(MyMediatorModule).Assembly);

    builder.RegisterAssemblyModules(typeof(Program).Assembly);

});

SignInRequestHandler类 #

public class SignInRequestHandler : RequestHandler<SignInRequest, SignInResponse>
{
    public SignInRequestHandler(DataContext dataContext) : base(dataContext)
    {
    }

    public async override Task<SignInResponse> Handle(SignInRequest request, CancellationToken cancellationToken)
    { ... }
}

SignInRequest类 #

public class SignInRequest : Request<SignInResponse>
{
    public string? Email { get; set; }
}

SignInResponse类 #

public class SignInResponse
{
    public bool IsStatus { get; set; }
}

RequestHandler抽象类 #

public abstract class RequestHandler<T, TResult> : IRequestHandler<T, TResult> where T : IRequest<TResult>
{
    internal readonly DataContext _dataContext;

    public RequestHandler(DataContext dataContext)
    {
        _dataContext = dataContext;
    }

    public abstract Task<TResult> Handle(T request, CancellationToken cancellationToken);
}

Request抽象类 #

public abstract class Request<T> : IRequest<T> 
{
}

错误原因分析 #

1. 程序集扫描范围错误：MyMediatorModule位于MyApp.Infrastructure程序集，但SignInRequestHandler属于MyApp.Application程序集（从异常信息的类型全名可确认），当前注册代码仅扫描了MyMediatorModule所在的程序集，未包含处理器所在的程序集，导致处理器未被注册。
2. 命名空间过滤逻辑冗余：即使目标类型符合命名空间规则，扫描范围错误也无法找到目标类型。

解决方法 #

方法一：扩展程序集扫描范围 #

修改MyMediatorModule中的注册代码，同时包含处理器所在的程序集：

builder.RegisterAssemblyTypes(
        typeof(MyMediatorModule).Assembly,
        typeof(SignInRequestHandler).Assembly)
    .Where(t => t.Namespace?.Contains("MyApp.Features") == true)
    .AsImplementedInterfaces();

方法二：在Startup中单独注册目标程序集 #

若不想修改MyMediatorModule，可在Startup的容器配置中直接注册MyApp.Application程序集的类型：

builder.Host.ConfigureContainer<ContainerBuilder>(builder =>
{
    builder.RegisterAssemblyModules(typeof(MyMediatorModule).Assembly);
    builder.RegisterAssemblyModules(typeof(Program).Assembly);
    
    // 新增：注册MyApp.Application中的处理器
    builder.RegisterAssemblyTypes(typeof(SignInRequestHandler).Assembly)
           .Where(t => t.Namespace?.Contains("MyApp.Features") == true)
           .AsImplementedInterfaces();
});

方法三：使用MediatR官方Autofac扩展包（推荐） #

借助官方扩展简化注册逻辑，避免手动扫描出错：

1. 安装NuGet包：Install-Package MediatR.Extensions.Autofac.DependencyInjection
2. 修改MyMediatorModule的Load方法：

protected override void Load(ContainerBuilder builder)
{
    builder.RegisterMediatR(typeof(SignInRequestHandler).Assembly);
}

该扩展会自动注册所有IRequestHandler、INotificationHandler等MediatR相关类型，无需手动处理扫描逻辑。

内容的提问来源于stack exchange，提问作者Illep