Filters in ASP.NET MVC enable you to run code before or after a particular stage in the execution pipeline. They can be configured globally per-controller or per-action.
There are different kinds of filters, and each filter is executed at a different stage in the pipeline. For example, action filters are executed when the action method is executed.
Let us use a simple example to see how an action filter (a type of filter) works.
I have created a simple controller, DateController, where I am just displaying the time. In this action method, I am using a predefined action filter by the name of ResponseCache, that caches the response for the duration specified in seconds. In the following code snippet, we have mentioned the duration as 600 seconds. So, the response will be cached for 10 minutes.
public class DateController : Controller {
[ResponseCache(Duration = 600)]
public IActionResult Index() {
return Content(DateTime.Now.ToShortTimeString());
}
}
When I run it for the first time, it displays the time as expected. But when you refresh the browser (which indirectly fires the request again), the time is not updated as the response is cached already by the application. In the following screenshot, even though the time is 7:43, the application is still showing as 7:40:
The following are the predefined types of filters available in ASP.NET Core.
These are used for authorization and are mainly intended to determine whether the current user is authorized for the request being made.
These are the filters that handle the request after authorization and are the last one to handle the request before it leaves the filter pipeline. They are used to implement caching or by passing the filter pipeline.
These wrap calls to individual action method calls and can manipulate the arguments passed in the action as well as the action result returned from it.