无法解析类型 'MediatR.IMediator' 的服务

Question

我尝试使用 CQRS 构建 .NET Core API，但由于 MediatR 错误我无法构建它：

System.AggregateException: '无法构建某些服务（验证服务描述符时出错 'ServiceType: Core.Infrastructure.Domain.Queries.IQueryBus Lifetime: Scoped ImplementationType: Core.Infrastructure.Bus.QueryBus'：尝试激活时无法解析类型 'MediatR.IMediator' 的服务 'Core.Infrastructure.Bus.QueryBus'.)'

我已经为我的 QueryBus 等添加了 'AddScope'。这是我的代码（适用于 AWS 的应用程序）：

public class Startup
    {
        public const string AppS3BucketKey = "AppS3Bucket";

        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public static IConfiguration Configuration { get; private set; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.AddAWSService<Amazon.S3.IAmazonS3>();

            services.AddScoped<IQueryBus, QueryBus>();
            services.AddScoped<IWarehouseRepository, WarehouseRepository>();
            services.AddScoped<IRequestHandler<GetAllWarehouseDepartmentsQuery, IEnumerable<WarehouseDepartmentDto>>, WarehouseQueryHandler>();
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }

查询总线：

using System.Threading.Tasks;
using Core.Infrastructure.Domain.Queries;
using MediatR;

namespace Core.Infrastructure.Bus
{
    public class QueryBus : IQueryBus
    {
        private readonly IMediator _mediator;

        public QueryBus(IMediator mediator)
        {
            _mediator = mediator;
        }

        public Task<TResponse> Send<TQuery, TResponse>(TQuery query) where TQuery : IQuery<TResponse>
        {
            return _mediator.Send(query);
        }
    }
}

IQueryBus:

using System.Threading.Tasks;

namespace Core.Infrastructure.Domain.Queries
{
    public interface IQueryBus
    {
        Task<TResponse> Send<TQuery, TResponse>(TQuery query) where TQuery : IQuery<TResponse>;
    }
}

感谢帮助

Answer 1

您没有在启动时注册 Mediatr 本身，因此 DI 容器无法解析它，正如错误提示的那样。

您可以从 NuGet 添加 MediatR DI 扩展，然后在启动时注册 MediatR：

To use, with an IServiceCollection instance:

services.AddMediatR(typeof(MyHandler));

or with an assembly:

services.AddMediatR(typeof(Startup).GetTypeInfo().Assembly);

https://github.com/jbogard/MediatR.Extensions.Microsoft.DependencyInjection

https://www.nuget.org/packages/MediatR.Extensions.Microsoft.DependencyInjection/

无法解析类型 'MediatR.IMediator' 的服务

Unable to resolve service for type 'MediatR.IMediator'

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