ASP.NET 核心工作者服务中的依赖注入

Question

我在 .NET Core 辅助角色服务中遇到了一些依赖注入问题。请参阅 Program.cs 文件中的以下代码。

public static void Main(string[] args)
{
    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Debug()
        .MinimumLevel.Override("Microsof)t", LogEventLevel.Warning)
        .Enrich.FromLogContext()
        .WriteTo.File(@"C:\MyApp_Log\Log.txt")
        .CreateLogger();

    try
    {
        Log.Information("Starting up the service.");
        CreateHostBuilder(args).Build().Run();
        return;
    }
    catch (Exception ex)
    {
        Log.Fatal(ex, "There was a problem starting the service");
        return;
    }
    finally
    {
        Log.CloseAndFlush();
    }

}
public static IHostBuilder CreateHostBuilder(string[] args)
{

    return Host.CreateDefaultBuilder(args)
        .UseWindowsService()
        .ConfigureServices((hostContext, services) =>
        {

            services.AddScoped<IMyAppCoreService, MyAppCoreService>();

            services.AddDbContext<MyAppCSContext>(options => options.UseSqlServer("Data Source=xx.xxx.xx.xxx;Database=Mydb;User ID = sa;Password=mypassword"));


            services.AddHostedService<Worker>();
        })
        .UseSerilog();
}

请参阅下面的 Worker.cs 文件代码

private readonly ILogger<Worker> _logger;
private readonly IMyAppCoreService _CoreService;

public Worker(ILogger<Worker> logger, IMyAppCoreService CoreService)
{
    _logger = logger;
    _CoreService = CoreService;
}
public override Task StartAsync(CancellationToken cancellationToken)
{
    _logger.LogInformation("The MyApp_CoreService has been Started...");
    return base.StartAsync(cancellationToken);
}
public override Task StopAsync(CancellationToken cancellationToken)
{
    _logger.LogInformation("The MyApp_CoreService has been stopped...");
    return base.StopAsync(cancellationToken);
}
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    while (!stoppingToken.IsCancellationRequested)
    {
        _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
        _CoreService.CheckAndProcessResult();
        await Task.Delay(1000, stoppingToken);
    }
}

当我运行上面的查询时，我得到了下面的查询。

验证服务描述符时出错

ServiceType: MyApp.CS.Business.Facade.IMyAppCoreService Lifetime: Scoped ImplementationType: MyApp.CS.Business.Services.MyAppCoreService': Unable to resolve service for type 'MyApp.CS.Data.Facade.ICommonRepository' while attempting to activate 'MyApp.CS.Business.Services.MyAppCoreService'.

你能告诉我哪里做错了吗？

编辑： 在我用 class 注册所有接口之后。然后我得到如下新错误。

Error while validating the service descriptor 'ServiceType: Microsoft.Extensions.Hosting.IHostedService Lifetime: Singleton ImplementationType: MyApp_CoreService.Worker': Cannot consume scoped service 'MyApp.CS.Business.Facade.IMyAppCoreService' from singleton 'Microsoft.Extensions.Hosting.IHostedService'.

Answer 1

您将 Serivce IMyAppCoreService 作为 Scoped 注入。范围服务只能由 ScopedServiceProvider.

解决

我的第一个猜测是你不是故意的 - 你打算将你的服务作为单例注入：

services.AddSingleton<IMyAppCoreService, MyAppCoreService>();

然而，这可能不起作用，因为您使用的是 EF Core，它将其类似上下文的 classes 作为作用域注入。您有两个选择：

让 EF Core 将其上下文 class 作为瞬态注入。我不建议这样做，因为您将负责处理它。如果你想完成它，这是怎么做的 (Startup.cs / Program.cs):

services.AddDbContext<YourContext>(opts => { ...config...}, ServiceLifetime.Transient);

手动创建范围：

将名为 ServiceProvider 的 IServiceProvider 属性注入 Worker 而不是 您的服务。

在 ExecuteAsync 循环中：

_logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
using (var scope = ServiceProvider.CreateScope())
{
  scope.ServiceProvider.GetRequiredService<IMyAppCoreService>().CheckAndProcessResult();
}
await Task.Delay(1000, stoppingToken);

这将巧妙地处理每个 Loop 的 EFCore-Data 上下文对象，在我看来是最干净的选择。

Answer 2

依赖注入：

 services.AddScoped<IMyAppCoreService, MyAppCoreService>();

 services.AddDbContext<MyAppCSContext>(options => options.UseSqlServer("Data Source=xx.xxx.xx.xxx;Database=Mydb;User ID = sa;Password=mypassword"), ServiceLifetime.Scoped);

工人class:

public class Worker : BackgroundService
{
    IServiceProvider _serviceProvider;

    public Worker(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        using (var scope = _serviceProvider.CreateScope())
        {
            scope.ServiceProvider.GetRequiredService<IMyAppCoreService>().CheckAndProcessResult();
        }

        await Task.Delay(1000, stoppingToken);
    }
}

来源https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-3.0&tabs=visual-studio#consuming-a-scoped-service-in-a-background-task

ASP.NET 核心工作者服务中的依赖注入

Dependency Injection in ASP.NET Core Worker Service

c#

windows-services

backgroundworker

.net-core

asp.net-core