如何正确解析要在 ASP.NET Core 3.1 中的 ConfigureServices() 中使用的服务？

Question

我有一个 ASP.NET 基于 Core 3.1 的应用程序。在应用程序启动期间，在 ConfigureServices(IServiceCollection services) 我想注册我的服务。但是在配置服务时，我想根据数据库中的设置启动应用程序。

这是我的代码

public void ConfigureServices(IServiceCollection services)
{
    // Register context
    services.AddDbContext<AppDbContext>(options =>
    {
        options.UseMySql(Configuration.GetConnectionString("MySqlServerConnection"));
    });

    // Reister the setting provider
    services.AddSingleton<IAppSetting, AppSettings>();

    // Create a resolver which is WRONG!!
    var resolver = services.BuildServiceProvider();

    var setting = resolver.GetService<IAppSetting>();

    List<string> allowedCors = new List<string>()
    {
         setting.MainUrl.ToString()
    };

    if (setting.HasCustomAssetsUri)
    {
        allowedCors.Add(settings.AssetsUrl.ToString());
    }

    if (settings.HasCustomPhotosUri)
    {
        allowedCors.Add(settings.PhotosUrl.ToString());
    }

    services.AddCors(options =>
    {
        options.AddPolicy("AllowSubDomainTraffic",
        builder =>
        {
            builder.WithOrigins(allowedCors.ToArray())
                   .AllowAnyHeader()
                   .AllowAnyMethod();
        });
    });

    // More services
}

正如您在上面的代码中看到的，我注册了 IAppSetting 但我立即想使用它来访问数据库，因此获取当前配置。我目前正在调用 services.BuildServiceProvider() 来创建一个新的解析器，然后我可以在其中使用它来创建 IAppSetting.

的实例

我的 AppSetting 实现依赖于同样注册的 AppDbContext。这是我的 AppSetting

public class AppSetting : IAppSetting
{
    private AppDbContext context;

    public AppSetting(AppDbContext context)
    {
        this.context = context;
    }

    // methods...
}

调用BuildServiceProvider() 将导致创建单独服务的额外副本。所以我尽量避免这样做。

如何在 ConfigureServices() 方法中正确注册然后解析 IAppSetting 以便我可以使用它来访问在数据库中找到的设置？

已更新

我尝试使用 Nkosi 提供的解决方案，但出现以下错误

System.InvalidOperationException: 'Cannot resolve scoped service 'IAppSetting' from root provider.'

这是完整的堆栈跟踪。

This exception was originally thrown at this call stack:
    Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteValidator.ValidateResolution(System.Type, Microsoft.Extensions.DependencyInjection.IServiceScope, Microsoft.Extensions.DependencyInjection.IServiceScope)
    Microsoft.Extensions.DependencyInjection.ServiceProvider.Microsoft.Extensions.DependencyInjection.ServiceLookup.IServiceProviderEngineCallback.OnResolve(System.Type, Microsoft.Extensions.DependencyInjection.IServiceScope)
    Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(System.Type, Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope)
    Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(System.Type)
    Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(System.IServiceProvider, System.Type)
    Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(Microsoft.Extensions.DependencyInjection.ServiceLookup.FactoryCallSite, Microsoft.Extensions.DependencyInjection.ServiceLookup.RuntimeResolverContext)
    Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitDisposeCache(Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceCallSite, Microsoft.Extensions.DependencyInjection.ServiceLookup.RuntimeResolverContext)
    ...
    [Call Stack Truncated]

Answer 1

services.AddSingleton<AppSetting>();
services.AddSingleton<IAppSetting>(ctx =>
    {
      var setting = ctx.GetRequiredService<AppSetting>();
      return setting;
    });

Answer 2

引用Use DI services to configure options

使用 DI 配置 CORS 选项，将所有逻辑移至配置委托中

//...

// Register context
services.AddDbContext<AppDbContext>(options => {
    options.UseMySql(Configuration.GetConnectionString("MySqlServerConnection"));
});

// Reister the setting provider
services.AddScoped<IAppSetting, AppSettings>(); 

//configure CORS options using DI
services.AddOptions<CorsOptions>()
    .Configure<IServiceScopeFactory>((options, sp) => {
        using(var scope = sp.CreateScope()) {
            IAppSetting settings = scope.ServiceProvider.GetRequiredService<IAppSetting>();
            List<string> allowedCors = new List<string>() {
                 setting.MainUrl.ToString()
            };

            if (setting.HasCustomAssetsUri) {
                allowedCors.Add(settings.AssetsUrl.ToString());
            }

            if (settings.HasCustomPhotosUri) {
                allowedCors.Add(settings.PhotosUrl.ToString());
            }
            options.AddPolicy("AllowSubDomainTraffic", builder => {
                builder.WithOrigins(allowedCors.ToArray())
                       .AllowAnyHeader()
                       .AllowAnyMethod();
            });
        }
    });

services.AddCors();

//...

这样一来，现在一切都推迟到实际需要的时候，您可以避免过早地构建服务集合。

Answer 3

考虑在以下示例中使用 IConfigureOptions（避免需要自己创建范围）：

public class ConfigureCorsOptions : IConfigureOptions<CorsOptions>
{
    private readonly IAppSetting _settings;

    public ConfigureCorsOptions(IAppSetting settings) => _settings = settings;


    public void Configure(CorsOptions options)
    {
        List<string> allowedCors = new List<string>()
        {
             _setting.MainUrl.ToString()
        };

        if (setting.HasCustomAssetsUri)
        {
            allowedCors.Add(_settings.AssetsUrl.ToString());
        }

        if (_settings.HasCustomPhotosUri)
        {
            allowedCors.Add(_settings.PhotosUrl.ToString());
        }

        options.AddPolicy("AllowSubDomainTraffic", builder =>
        {
           builder.WithOrigins(allowedCors.ToArray())
                  .AllowAnyHeader()
                  .AllowAnyMethod();
        });
    }
}

要将此 class 注册到 DI 容器，您可以使用类似的东西：

services.AddTransient<IConfigureOptions<CorsOptions>, ConfigureCorsOptions>();

如何正确解析要在 ASP.NET Core 3.1 中的 ConfigureServices() 中使用的服务？

How to correctly resolve services to use in the ConfigureServices() in ASP.NET Core 3.1?

asp.net-core

.net-core

asp.net-core-mvc

asp.net-core-3.0

asp.net-core-3.1