某些服务无法在.NET 8辅助服务中构建

Question

这是我的

program.cs

:

var builder = Host.CreateApplicationBuilder(args);
builder.Services.AddSingleton<cMain>();

// Ensure cMain is constructed before using it to get the connection string
var serviceProvider = builder.Services.BuildServiceProvider();
var cMainInstance = serviceProvider.GetRequiredService<cMain>();
var connectionString = cMainInstance.ConnectionString;

// Register the DbContext with the correct connection string
builder.Services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(connectionString));
builder.Services.AddScoped<IUnitOfWork, UnitOfWork>();
builder.Services.AddHostedService<Worker>();

var host = builder.Build();

host.Run();

这是我的

UnitOfWork

和

IUnitOfWork

:

public class UnitOfWork : IUnitOfWork
{
    private readonly ApplicationDbContext _db;

    public UnitOfWork(ApplicationDbContext db)
    {
        _db = db;
       BreadCrumbs = new BreadCrumbRepository(_db);
    }
    
    public IBreadCrumbRepository BreadCrumbs { get; private set; }

    public void Save()
    {
        _db.SaveChanges();
    }
}

public interface IUnitOfWork
{
    IBreadCrumbRepository BreadCrumbs { get; }
    void Save();
}

我正在尝试将

IUnitOfWork

注入到工作线程中，但出现以下错误：

public class Worker : BackgroundService
{
     private readonly ILogger<Worker> _logger;
     private readonly cMain _cmain;
     private readonly IConfiguration _configuration;
     private readonly IUnitOfWork _uow;

     public Worker()
     {
     }

     public Worker(ILogger<Worker> logger, IConfiguration configuration, IUnitOfWork uow)
     {
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
         _configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
         _uow = uow ?? throw new ArgumentNullException(nameof(uow));
         _cmain = new cMain(_configuration);
     }

     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
         while (!stoppingToken.IsCancellationRequested)
         {
             var breadCrumb = new BreadCrumb
             {
                 Application = Assembly.GetExecutingAssembly().GetName().Name,
                 DateTime = DateTime.Now,
                 Description = "Test",
                 EnquiryHeader_ID = 1,
                 EventName = "Test",
                 ReferenceID = 1,
                 Result = "Test"
             };

             //await _uow.BreadCrumbs.AddAsync(breadCrumb);

             if (_logger.IsEnabled(LogLevel.Information))
             {
                 _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
             }
             await Task.Delay(1000, stoppingToken);
         }
     }
}

我得到的错误如下

抛出异常：Microsoft.Extensions.DependencyInjection.dll 中的“System.AggregateException”
部分服务无法构建

如果有此异常的处理程序，则程序可以安全地继续。

我真的很感激你指出我哪里出了问题或我遗漏了什么

我期望应用程序能够运行并消耗工作者类中的

IUnitOfWork

。当我删除 DI 时，它会运行。

Answer 1

问题在于该服务已注册为范围

builder.Services.AddScoped<IUnitOfWork, UnitOfWork>();

它需要是后台工作者的单例。

如果您需要将生命周期限定为 UnitOfWork 的范围，请在此处阅读有关如何在工作线程中创建范围的信息。 https://learn.microsoft.com/en-us/dotnet/core/extensions/scoped-service