'某些服務無法構造（驗證服務描述符時出錯'ServiceType：IHostedService

我正在使用 .NET 5，我想使用IHostedServiceclassess 運行后臺任務，如您所見：

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
}

所以我必須將它注入到服務集合中，如您所見：

services.AddHostedService<PasargadJobs>();

但是在添加這個之后我得到了這個錯誤：

System.AggregateException：'某些服務無法構造（驗證服務描述符時出錯'ServiceType：Microsoft.Extensions.Hosting.IHostedService Lifetime：Singleton ImplementationType：MIMS.Portal.ScheduleJobs.PasargadJobs'：無法使用范圍服務'Microsoft .EntityFrameworkCore.DbContextOptions`1[MIMS.Portal.Infrustructure.Repositories.AppDbContext]' 來自單例'Microsoft.Extensions.Hosting.IHostedService'。）'

這是我的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>();

uj5u.com熱心網友回復：

您的托管服務是單例的，并且您間接依賴于范圍服務：

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

您可以通過以下方式解決問題

注入IServiceScopeFactory您的托管服務并手動創建服務范圍，如下所示

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

不要將CreateScopeandGetRequiredService放在托管服務的建構式中：由于托管服務是單例的，建構式只會被呼叫一次，因此創建的實體scope.ServiceProvider.GetRequiredService<T>()也將被創建一次。因此，在這種情況下，您將使用被設計為短暫存在的服務作為永遠活著的單身人士。使用后也不要忘記丟棄scope。

由于看起來您正在使用 Entity Framework Core 和上述方法的替代方案，您還可以考慮重構要使用的服務，IDbContextFactory<TContext> 以便將它們注冊為單例服務。

標籤：asp.net 核心 依赖注入 后台任务 asp.net-core-hosted-services 服务集合

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