ASP.NET核心2中的依赖注入

Question

更新

我将启动更改为：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Actio.Api.Handlers;
using Actio.Api.Repositories;
using Actio.Common.Auth;
using Actio.Common.Events;
using Actio.Common.Mongo;
using Actio.Common.RabbitMq;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Actio.Api
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            services.AddJwt(Configuration);
            services.AddRabbitMq(Configuration);
            services.AddMongoDB(Configuration);
            services.AddScoped<IEventHandler<ActivityCreated>, ActivityCreatedHandler>();
            services.AddScoped<IActivityRepository, ActivityRepository>();

        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            // app.ApplicationServices.GetService<IDatabaseInitializer>().InitializeAsync();

            using (var serviceScope = app.ApplicationServices.CreateScope())
            {
                serviceScope.ServiceProvider.GetService<IDatabaseInitializer>().InitializeAsync();
            }
            app.UseAuthentication();
            app.UseMvc();
        }
    }
}

但是现在我在SubscribeToEvent：中出现了错误，无法解析作用域服务。

'Actio.Common.Events.IEventHandler`1[Actio.Common.Events.ActivityCreated]' from root provider.' 

在我的ServiceHost.cs里。

ServiceHost.cs

using System;
using Actio.Common.Commands;
using Actio.Common.Events;
using Actio.Common.RabbitMq;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using RawRabbit;

namespace Actio.Common.Services
{
    public class ServiceHost : IServiceHost
    {
        private readonly IWebHost _webHost;

        public ServiceHost(IWebHost webHost)
        {
            _webHost = webHost;
        }

        public void Run() => _webHost.Run();

        public static HostBuilder Create<TStartup>(string[] args) where TStartup : class
        {
            Console.Title = typeof(TStartup).Namespace;
            var config = new ConfigurationBuilder()
                .AddEnvironmentVariables()
                .AddCommandLine(args)
                .Build();
            var webHostBuilder = WebHost.CreateDefaultBuilder(args)
                .UseConfiguration(config)
                .UseStartup<TStartup>();

            return new HostBuilder(webHostBuilder.Build());
        }

        public abstract class BuilderBase 
        {
            public abstract ServiceHost Build();
        }

        public class HostBuilder : BuilderBase
        {
            private readonly IWebHost _webHost;
            private IBusClient _bus;

            public HostBuilder(IWebHost webHost)
            {
                _webHost = webHost;
            }

            public BusBuilder UseRabbitMq()
            {
                _bus = (IBusClient)_webHost.Services.GetService(typeof(IBusClient));

                return new BusBuilder(_webHost, _bus);
            }

            public override ServiceHost Build()
            {
                return new ServiceHost(_webHost);
            }
        }

        public class BusBuilder : BuilderBase
        {
            private readonly IWebHost _webHost;
            private IBusClient _bus; 

            public BusBuilder(IWebHost webHost, IBusClient bus)
            {
                _webHost = webHost;
                _bus = bus;
            }

            public BusBuilder SubscribeToCommand<TCommand>() where TCommand : ICommand
            {
                var handler = (ICommandHandler<TCommand>)_webHost.Services
                    .GetService(typeof(ICommandHandler<TCommand>));
                _bus.WithCommandHandlerAsync(handler);

                return this;
            }

            public BusBuilder SubscribeToEvent<TEvent>() where TEvent : IEvent
            {
                var handler = (IEventHandler<TEvent>)_webHost.Services
                    .GetService(typeof(IEventHandler<TEvent>));
                _bus.WithEventHandlerAsync(handler);

                return this;
            }

            public override ServiceHost Build()
            {
                return new ServiceHost(_webHost);
            }
        }
    }
}

我最近开始用RabbitMQ学习微服务。经过很大的努力，我得到了一个代码示例，但是我无法运行它，因为它给出了错误:"System.InvalidOperationException: 'Cannot resolve scoped service 'Actio.Common.Mongo.IDatabaseInitializer' from root provider.'"。

我希望理解这段代码，以便更好地理解Microservices。

Code-Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Actio.Api.Handlers;
using Actio.Api.Repositories;
using Actio.Common.Auth;
using Actio.Common.Events;
using Actio.Common.Mongo;
using Actio.Common.RabbitMq;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Actio.Api
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            services.AddJwt(Configuration);
            services.AddRabbitMq(Configuration);
            services.AddMongoDB(Configuration);
            services.AddScoped<IEventHandler<ActivityCreated>, ActivityCreatedHandler>();
            services.AddScoped<IActivityRepository, ActivityRepository>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
          //Giving Error in below line


app.ApplicationServices.GetService<IDatabaseInitializer>().InitializeAsync();
                app.UseAuthentication();
                app.UseMvc();
            }
        }
    }

有人能帮忙吗?这样我就可以调试了，我也有了更好的理解。

谢谢

Answer 1

下面的错误试图告诉您，您正在将IDatabaseInitializer注册为一个作用域服务，但试图在范围之外访问它。

"System.InvalidOperationException: 'Cannot resolve scoped service 'Actio.Common.Mongo.IDatabaseInitializer' from root provider.'"

尝试创建一个作用域，然后使用以下服务：

using (var serviceScope = app.ApplicationServices.CreateScope())
{
    serviceScope.ServiceProvider.GetService<IDatabaseInitializer>().InitializeAsync();
}

Answer 2

解决方案是禁用范围验证。

因此，在第31-32行之间的文件src\actio.common\services\servicehost.cs中添加以下内容：

.UseDefaultServiceProvider(options => options.ValidateScopes = false)

解决这个问题的另一种替代方法是从services.AddScoped转变为services.AddSingleton in program.cs，使用单例也可以避免所有的范围验证。