ASP.NET Core 8 Web API：无法从单例注册作用域服务

Question

在我的 API 中，我使用

AddHostedService

注册了一些服务，这些服务需要注入一些接口，例如：

Program.cs:

builder.Services.AddScoped<IHypervisorRepository, HypervisorRepository>();
builder.Services.AddScoped<IAccountRepository, AccountRepository>();
builder.Services.AddScoped<ICloudStackDbUnitOfWork, CloudStackDbUnitOfWork>();
builder.Services.AddScoped<ICloudStackCoreConnectionFactory, MySqlCloudStackCoreConnectionFactory>();

builder.Services.AddScoped<IJobUtility, JobUtility>();
builder.Services.AddScoped<IVdcUnitOfWork, VdcUnitOfWork>();
builder.Services.AddScoped<IMemoryCache, MemoryCache>();

builder.Services.AddHostedService<CheckDatabaseHealthBackgroundService>();

CheckDatabaseHealthBackgroundService.cs:

public sealed class CheckDatabaseHealthBackgroundService : BackgroundService, IDisposable
{
    private readonly IServiceProvider _provider;
    private readonly IJobUtility _jobUtility;
    private readonly IVdcUnitOfWork _unitOfWork;
    private readonly ICloudStackCoreConnectionFactory _connFactory;
    private readonly IMemoryCache _cache;
    private readonly ILogger<CheckDatabaseHealthBackgroundService> _logger;
    
    public CheckDatabaseHealthBackgroundService(
        IServiceProvider provider,
        IJobUtility jobUtility,
        IVdcUnitOfWork unitOfWork,
        ICloudStackCoreConnectionFactory connFactory,
        IMemoryCache cache,
        ILogger<CheckDatabaseHealthBackgroundService> logger)
    {
        _provider = provider;
        _jobUtility = jobUtility;
        _unitOfWork = unitOfWork;
        _connFactory = connFactory;
        _cache = cache;
        _logger = logger;
    }

但是在我启动 API 后，会抛出以下异常：

System.InvalidOperationException：验证服务描述符“ServiceType：Microsoft.Extensions.Hosting.IHostedService 生命周期时出错：单例实现类型：CloudStackData.WebAPI.RefreshDiskTypeBackgroundService”：无法使用单例“Microsoft”中的作用域服务“Vdc.Libs.Data.IVdcUnitOfWork” .Extensions.Hosting.IHostedService'.

System.InvalidOperationException：无法使用单例“Microsoft.Extensions.Hosting.IHostedService”中的范围服务“Vdc.Libs.Data.IVdcUnitOfWork”

读完这个错误后，我得出结论，我应该将

CheckDatabaseHealthBackgroundService

所需的服务添加为单例，而不是限定范围，所以我尝试了：

Program.cs:

builder.Services.AddScoped<IHypervisorRepository, HypervisorRepository>();
builder.Services.AddScoped<IAccountRepository, AccountRepository>();
builder.Services.AddScoped<ICloudStackDbUnitOfWork, CloudStackDbUnitOfWork>();
builder.Services.AddScoped<ICloudStackCoreConnectionFactory, MySqlCloudStackCoreConnectionFactory>();

builder.Services.AddSingleton<IJobUtility, JobUtility>();
builder.Services.AddSingleton<IVdcUnitOfWork, VdcUnitOfWork>();
builder.Services.AddSingleton<IMemoryCache, MemoryCache>();

builder.Services.AddHostedService<CheckDatabaseHealthBackgroundService>();

现在抛出的异常是：

System.InvalidOperationException：验证服务描述符“ServiceType：Microsoft.Extensions.Hosting.IHostedService 生命周期时出错：单例实现类型：CloudStackData.WebAPI.RefreshDiskTypeBackgroundService”：无法使用单例“Vdc”中的作用域服务“Vdc.Libs.Data.DbContextWrite” .Libs.Data.IVdcUnitOfWork'.

我开始陷入困境。

VdcUnitOfWork

是我们创建的自定义类：

public sealed class VdcUnitOfWork : EFDbUnitOfWork<DbContextWrite>, IVdcUnitOfWork, IUnitOfWork, IDisposable, IDbContextWrapper
{
    public VdcUnitOfWork(DbContextWrite dbContext)
        : base(dbContext)
    {
    }
}

并且

DbContextWrite

是另一个自定义类：

public abstract class DbContextWrite : DbContext
{
    protected DbContextWrite([NotNull] DbContextOptions options)
        : base(options)
    {
    }
}

事实是，在使用

AddHostedService

添加托管服务后，我无法再运行 API（我有四个托管服务，但为了简化而只放了一个）。

有什么帮助吗？

Answer 1

要在

HostedService

（单例）中使用作用域服务，您需要注入

IServiceScopeFactory

（使用

.NET 8.0

中的主构造函数）：

public sealed class CheckDatabaseHealthBackgroundService
      (IServiceScopeFactory scopeFactory) : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
         // get scoped services:
         using var scope = scopeFactory.CreateScope();
         var jobUtility = scope.ServiceProvider.GetService<IJobUtility>();
         var unitOfWork = scope.ServiceProvider.GetService<IVdcUnitOfWork>();
         var memoryCache = scope.ServiceProvider.GetService<IMemoryCache>();

         // Use services here
    }
}