Service Fabric Core3.1中MediatR依赖注入注册异常问题

在基于.NET Core 3.1的Service Fabric应用中集成MediatR时，QueryHandler不依赖仓储可正常注册；但添加IRepository<myDto>依赖后，无法构造请求处理器，报错无法解析该仓储服务。

DI配置代码 #

var assembly1 = Assembly.GetExecutingAssembly();
var assembly2 = typeof(GetSomeThingQuery).Assembly;
var assembly3 = typeof(IRepository<myDto>).Assembly;
var assembly4 = typeof(myDto).Assembly;

var provider = new ServiceCollection()
    .AddLogging()
    .AddMediatR(assembly1, assembly2, assembly3, assembly4)
    .AddSingleton<IApiExceptionService, ApiExceptionService>()
    .BuildServiceProvider();

ServiceRuntime.RegisterServiceAsync("ApiServiceType",
    context => new ApiService(context, provider.GetService<IApiExceptionService>(), provider.GetService<IMediator>())).GetAwaiter().GetResult();

处理器代码 #

namespace Query
{
    public class GetSomeThingQuery: IRequest<List<myDto>>
    {
        public string para1{ get; set; }
        public string para2 { get; set; }
    }

    public class GetSomeThingQueryHandler : IRequestHandler<GetSomeThingQuery, List<myDto>>
    {
        private readonly IRepository<myDto> _repository;

        public GetSomeThingQueryHandler (IRepository<myDto> repository)
        {
            _repository = repository;
        }

        public async Task<List<myDto>> Handle(GetSomeThingQueryHandler Query request, CancellationToken cancellationToken)
        {
            var test =  await _repository.CallTheDatabaseAndGetTheResult(request.para1);
            return null; //this is just here as a place holder.
        }
    }
}

错误信息 #

System.InvalidOperationException: Error constructing handler for request of type MediatR.IRequestHandler`2[Query.GetSomeThingQuery,System.Collections.Generic.List`1[Sql.myDto]]. Register your handlers with the container. See the samples in GitHub for examples.
 ---> System.InvalidOperationException: Unable to resolve service for type 'IRepository`1[myDto]' while attempting to activate 'Query.GetSomeThingQuery'.
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, Int32 slot)

1. 修复处理器Handle方法的参数类型错误 #

处理器的Handle方法参数类型写错了，应该是GetSomeThingQuery而非GetSomeThingQueryHandler，修正后代码如下：

public async Task<List<myDto>> Handle(GetSomeThingQuery request, CancellationToken cancellationToken)
{
    var test = await _repository.CallTheDatabaseAndGetTheResult(request.para1);
    return null; // 占位用，实际返回对应结果
}

这个笔误会导致MediatR无法正确匹配请求与处理器，甚至触发错误的类型解析逻辑。

2. 在DI容器中注册仓储的实现类 #

当前DI配置中仅注册了MediatR和IApiExceptionService，但未注册IRepository<myDto>的具体实现。需要添加仓储的注册代码，根据实际业务需求选择合适的生命周期（单例、作用域或瞬态）：

var provider = new ServiceCollection()
    .AddLogging()
    .AddMediatR(assembly1, assembly2, assembly3, assembly4)
    .AddSingleton<IApiExceptionService, ApiExceptionService>()
    // 添加仓储注册，替换为你的实际实现类
    .AddSingleton<IRepository<myDto>, MyRepositoryImplementation<myDto>>()
    .BuildServiceProvider();

内容的提问来源于stack exchange，提问作者krock28