c# - 无法解析 'MediatR.IMediator'类型的服务

Question

我尝试使用CQRS制作.NET Core API，但由于MediatR错误而无法构建它:

System.AggregateException:'某些服务无法构造(验证服务描述符'ServiceType:Core.Infrastructure.Domain.Queries.IQueryBus的生存期:范围实现类型:Core.Infrastructure.Bus.QueryBus':无法解析服务尝试激活“Core.Infrastructure.Bus.QueryBus”时，类型为“MediatR.IMediator”。)”

我已经为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();
            });
        }
    }

QueryBus:

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

您尚未在启动时注册Mediatr本身，因此DI容器无法解决它，如错误所示。

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/