ASP.NET Core 使用 ActionFilter 實作快取

建立一個 CacheActionFilter class，實作 Attribute 和 IAsyncActionFilter

public class CacheActionFilter : Attribute, IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
		await next();
    }
}

可以拿到傳入 action 的參數和它的名稱當成快取的 key

public class CacheActionFilter : Attribute, IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
		var args = context.ActionArguments.Select(a => $"{JsonConvert.SerializeObject(a.Value)}");
        var arg = string.Join(",", args);
        var cacheKey = $"{context.ActionDescriptor.DisplayName}-{arg}";

		await next();
    }
}

可以拿到 response 之後使用 MemoryCache 快取起來
- 這裡假設 API 的返回都只有 OKObjectResut
- 為了之後方便使用，IMemoryCache 直接從 RequestServices 拿

public class CacheActionFilter : Attribute, IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
		var args = context.ActionArguments.Select(a => $"{JsonConvert.SerializeObject(a.Value)}");
        var arg = string.Join(",", args);
        var cacheKey = $"{context.ActionDescriptor.DisplayName}-{arg}";

		await next();
		if (response.Result is OkObjectResult result)
		{
			var memory = response.HttpContext.RequestServices.GetService<IMemoryCache>();
			memory.Set(cacheKey, result.Value);
		}
    }
}

使用 MemoryCache 要記得在 startup 註冊

public void ConfigureServices(IServiceCollection services)
{
	services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    services.AddMemoryCache();
}

因為已經有把 response 快取了，所以可以在執行 next 之前判斷，如果有快取就直接返回快取，沒有的話就再執行 next

public class CacheActionFilter : Attribute, IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
		var args = context.ActionArguments.Select(a => $"{JsonConvert.SerializeObject(a.Value)}");
		var arg = string.Join(",", args);
		var cacheKey = $"{context.ActionDescriptor.DisplayName}-{arg}";

		var memoryCache = context.HttpContext.RequestServices.GetService<IMemoryCache>();

		if (memoryCache.TryGetValue(cacheKey, out object cacheResult))
		{
			context.Result = new OkObjectResult(cacheResult);
			return;
		}

		var response = await next();

		if (response.Result is OkObjectResult result)
		{
			memoryCache.Set(cacheKey, result.Value);
		}
    }
}

因為現在是有快取就不執行，應該是有點奇怪，應該要改成由外面決定快取的時間，如果超過一定的時間，還是要執行會比較合理

public class CacheActionFilter : Attribute, IAsyncActionFilter
{
	private readonly int _duration;
	public CacheActionFilter(int duration)
	{
		_duration = duration;
	}

    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
		var args = context.ActionArguments.Select(a => $"{JsonConvert.SerializeObject(a.Value)}");
		var arg = string.Join(",", args);
		var cacheKey = $"{context.ActionDescriptor.DisplayName}-{arg}";

		var memoryCache = context.HttpContext.RequestServices.GetService<IMemoryCache>();

		if (memoryCache.TryGetValue(cacheKey, out object cacheResult))
		{
			context.Result = new OkObjectResult(cacheResult);
			return;
		}

		var response = await next();

		if (response.Result is OkObjectResult result)
		{
			memoryCache.Set(cacheKey, result.Value, TimeSpan.FromSeconds(_duration));
		}
    }
}

實際測試使用，一直 refresh 的話，時間每隔 5 秒才會變

[HttpGet]
[CacheActionFilter(5)]
public ActionResult<string> Get(string name)
{
    return Ok($"{name} - {DateTime.Now.ToString()}");
}