如何從ActionFilterAttribute訪問AppSettings

Question

我需要從ActionFilterAttribute中的appsettings.json文件中獲取值。 我點擊了此鏈接（ 如何從ASP.NET Core中的ActionFilterAttribute訪問AppSettings ），但這無濟於事，因為我需要將參數傳遞給自定義過濾器，並且還需要使用來自appsettings.json的參數。 例如

//Filter.cs

[AttributeUsage(AttributeTargets.Method)]
public class ThrottleAttribute : ActionFilterAttribute
{
    public string Count { get; set; }

    private static MemoryCache Cache { get; } = new MemoryCache(new MemoryCacheOptions());

    public override void OnActionExecuting(ActionExecutingContext actionExecutingContext)
    {
        //Compare this.Count with GetValueFromAppSettings.json
    }
}

//Controller.cs

[ApiController]
[Route("api/[controller]")]
public class ValuesController : BaseController
{
    // GET api/values
    [HttpGet]
    [Authorize]
    [Throttle(Count = 15)]
    public ActionResult<IEnumerable<string>> Get()
    {
        return new[] { "value1", "value2" };
    }

}

Answer 1

appsettings.json應該在DI中注冊，因此您可以將IConfiguration傳遞給ThrottleAttribute構造函數並通過DI從中獲取值，但是您需要創建工廠才能使其工作：

public class ThrottleAttributeFactory: ActionFilterAttribute, IFilterFactory
{
    public string Count { get; set; }

    public bool IsReusable => false;

    public IFilterMetadata CreateInstance(IServiceProvider serviceProvider)
    {
        var attribute = serviceProvider.GetService<ThrottleAttribute>();

        attribute.Count = Count;

        return attribute;
    }
}

屬性：

public class ThrottleAttribute : ActionFilterAttribute
{
    private readonly IConfiguration _config;

    public string Count { get; set; }

    public ThrottleAttribute(IConfiguration config)
    {
        _config = config;
    }
    //rest of code omitted
}

在您的方法中：

{
    var value = _config.GetValue<int>("json:key");
}

並在控制器中將[Throttle(Count = 15)]替換為[ThrottleAttributeFactory(Count = 15)] 。

還要注冊屬性： services.AddScoped<ThrottleAttribute>();

Answer 2

在您的情況下， IFilterFactory實現將是最佳選擇。

public class ThrottleAttributeFactory : Attribute, IFilterFactory
{
    public string Count { get; set; }

    public bool IsReusable => false;

    public IFilterMetadata CreateInstance(IServiceProvider serviceProvider)
    {
        var filter = serviceProvider.GetService<ThrottleAttribute>();

        filter.Count = Count;

        return filter;
    }
}

然后可以將其注入構造函數

private readonly IConfiguration config;

public ThrottleAttribute(IConfiguration config)
{
    this.config = config;
}

您必須將[Throttle(Count = 15)]更改為[ThrottleAttributeFactory(Count = 15)]

並且不要忘記在Startup.cs中注冊IConfiguration和屬性：

public void ConfigureServices(IServiceCollection services)
{
   ...    
   services.AddSingleton<IConfiguration>(Configuration);
   services.AddScoped<ThrottleAttribute>();
}

Answer 3

您可以在Throttle類中添加靜態屬性，並將配置值存儲在其中。 然后，可以在啟動類中設置該值。

[AttributeUsage(AttributeTargets.Method)]
public class ThrottleAttribute : ActionFilterAttribute
{
    public string Count { get; set; }

    public static string ConfigCount { get; set; }

    private static MemoryCache Cache { get; } = new MemoryCache(new MemoryCacheOptions());

    public override void OnActionExecuting(ActionExecutingContext actionExecutingContext)
    {
        //Compare this.Count with GetValueFromAppSettings.json
    }
}

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    ThrottleAttribute.ConfigCount = Configuration.GetValue<int>("key");
}