'某些服务无法构建（验证服务描述符时出错'ServiceType：IHostedService

Question

我正在使用 .NET 5，我想 运行 使用 IHostedService 类的后台任务，如您所见：

public class PasargadJobs : IHostedService, IDisposable
{
    private Timer _timer = null!;
    readonly  ITerminalService _terminalService;
    readonly  IMessageService _messageService;
    readonly IMerchantService _merchantService;
    
    public PasargadJobs(
        IMerchantService merchantService,
        ITerminalService terminalService,
        IMessageService messageService)
    {
        _messageService = messageService;
        _terminalService = terminalService;
        _merchantService = merchantService;
    }
    
    //other parts of code are removed for short code
}

所以我必须将它注入服务集合，如您所见：

services.AddHostedService<PasargadJobs>();

但是在添加这个之后我得到了这个错误：

System.AggregateException: 'Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: Microsoft.Extensions.Hosting.IHostedService Lifetime: Singleton ImplementationType: MIMS.Portal.ScheduleJobs.PasargadJobs': Cannot consume scoped service 'Microsoft.EntityFrameworkCore.DbContextOptions`1[MIMS.Portal.Infrustructure.Repositories.AppDbContext]' from singleton 'Microsoft.Extensions.Hosting.IHostedService'.)'

这是我的startup.cs

services.AddExpressiveAnnotations();

//--- DB Context ---//
services.AddTransient<AppDbContext, AppDbContext>();
//--- Repositories ---//
services.AddTransient(typeof(IGenericRepository<>), typeof(GenericRepository<>));
services.AddTransient<IMerchantRepository, MerchantRepository>();
services.AddTransient<IBankAccountRepository, BankAccountRepository>();
services.AddTransient<IBankRepository, BankRepository>();
services.AddTransient<IGeoRepository, GeoRepository>();
services.AddTransient<IDepartmentRepository, DepartmentRepository>();
services.AddTransient<IDeviceRepository, DeviceRepository>();
services.AddTransient<IInvoiceRepository, InvoiceRepository>();
services.AddTransient<IStoreRepository, StoreRepository>();
services.AddTransient<ITerminalRepository, TerminalRepository>();
services.AddTransient<ITicketRepository, TicketRepository>();
services.AddTransient<IUserRepository, UserRepository>();
services.AddTransient<IFileRepository, FileRepository>();
services.AddTransient<IPartnerRepository, PartnerRepository>();
services.AddTransient<IStoreScopeRepository, StoreScopeRepository>();
services.AddTransient<ICommentRepository, CommentRepository>();
services.AddTransient<INewsRepository, NewsRepository>();
services.AddTransient<IPosBrandRepository, PosBrandRepository>();
//-- Services --//
services.AddTransient<IMerchantService, MerchantService>();
services.AddTransient<IBankAccountService, BankAccountService>();
services.AddTransient<IBankService, BankService>();
services.AddTransient<IGeoService, GeoService>();
services.AddTransient<IDepartmentService, DepartmentService>();
services.AddTransient<IDeviceService, DeviceService>();
services.AddTransient<IInvoiceService, InvoiceService>();
services.AddTransient<IStoreService, StoreService>();
services.AddTransient<ITerminalService, TerminalService>();
services.AddTransient<ITicketService, TicketService>();
services.AddTransient<IUsersService, UsersService>();
services.AddTransient<IFilesManagerService, FilesManagerService>();
services.AddTransient<IMessageService, MessageService>();
services.AddTransient<IPartnerService, PartnerService>();
services.AddTransient<IStoreScopeService, StoreScopeService>();
services.AddTransient<INewsService, NewsService>();
services.AddTransient<ICommentService, CommentService>();
services.AddTransient<IPosBrandService, PosBrandService>();

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

services
    .AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(option =>
    {
        option.TokenValidationParameters = new TokenValidationParameters
        {
            ValidateIssuer = true,
            ValidateAudience = true,
            ValidateLifetime = true,
            ValidateIssuerSigningKey = true,
            ValidIssuer = "localhost",
            ValidAudience = "localhost",
            IssuerSigningKey = new SymmetricSecurityKey(
                Encoding.UTF8.GetBytes("wevhgfrtyhasdfghjklzxcvbnm"))
        };
    });
    
services.AddHostedService<PasargadJobs>();

Answer 1

您的托管服务是单例的，并且您间接依赖于作用域服务：

Cannot consume scoped service 'Microsoft.EntityFrameworkCore.DbContextOptions`1[MIMS.Portal.Infrustructure.Repositories.AppDbContext]' from singleton 'Microsoft.Extensions.Hosting.IHostedService'

您可以通过以下方式解决问题

将 IServiceScopeFactory 注入您的托管服务并手动创建服务范围，如下所示

using var scope = _serviceScopeFactory.CreateScope();
var service = scope.ServiceProvider.GetRequiredService<IScopedService>();

不要将 CreateScope 和 GetRequiredService 放在托管服务的构造函数中：由于托管服务是单例的，构造函数将只被调用一次，因此实例由 scope.ServiceProvider.GetRequiredService<T>()也会创建一次。因此，在这种情况下，您将使用设计为 short-lived 的服务作为永远活着的单身人士。也不要忘记在使用后处理 scope。

因为看起来您正在使用 Entity Framework 核心和上述方法的替代方法，您还可以考虑重构您的服务以使用 IDbContextFactory<TContext> 以便它们可以注册为单一服务。

Answer 2

在您的 class 中实施 BackgroundService。它已经实现了 IHostedService 和 IDisposable

public class PasargadJobs : BackgroundService

services.AddHostedService<PasargadJobs>();