如何从AppSettings访问ActionFilterAttribute

Question

我需要从appsettings.json文件中获取ActionFilterAttribute中的值。我遵循了这个链接(How can I access AppSettings from an ActionFilterAttribute in ASP.NET Core)，但它对我没有帮助，因为我需要将参数传递给我的自定义过滤器，并使用来自appsettings.json的一些参数。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 .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

在您的例子中，IFilterFactory实现将是最佳选择。

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，您可以将它注入构造函数。

private readonly IConfiguration config;

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

您必须将[Throttle(Count = 15)]更改为[ThrottleAttributeFactory(Count = 15)]

不要忘记在IConfiguration中注册Startup.cs和属性：

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

Answer 2

appsettings.json应该在DI中注册，这样您就可以将IConfiguration传递给ThrottleAttribute构造函数并通过DI从它获得值，但是您需要创建工厂才能使其工作：

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;
    }
}

属性：

public class ThrottleAttribute : ActionFilterAttribute
{
    private readonly IConfiguration _config;

    public string Count { get; set; }

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

用你的方法：

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

在控制器中，用[Throttle(Count = 15)]代替[ThrottleAttributeFactory(Count = 15)]。

还注册属性：services.AddScoped<ThrottleAttribute>();

Answer 3

您可以向Throttle类添加一个静态属性，并将配置值存储在其中。然后，在您的启动类中，可以设置该值。

[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");
}