Skipping ActionFilters in ASP.NET MVC

In the previous post I showed how you can use an action filter to execute code both before and after an action method and how to apply the filter globally.

I found myself in a scenario where I wanted to run the action filter almost globally. I needed to exclude all actions methods in one controller and one action method in another controller.

This is easily done with the use of an Attribute, see here for more.

Create a SkipImportantTaskAttribute like so –

  public class SkipImportantTaskAttribute : Attribute {}

I then decorate the relevant action methods or controllers with this attribute.
To skip an entire controller do this –

    [SkipImportantTask]
    public class CustomersController : Controller

To skip just a single action method do this –

	[SkipImportantTask]
	public ActionResult Index()

Change the OnActionExecuted (or OnActionExecuting) method of the action filter to the following

 
public override void OnActionExecuted(ActionExecutedContext filterContext)
{
	bool skipImportantTaskFilter = filterContext.ActionDescriptor.ControllerDescriptor.IsDefined(typeof(SkipImportantTaskAttribute), true) ||
		filterContext.ActionDescriptor.IsDefined(typeof(SkipImportantTaskAttribute), true);

	if (!skipImportantTaskFilter)
	{
		PerformModelAlteration(filterContext);
	}

	base.OnActionExecuted(filterContext);
}

Now if SkipImportantTaskAttribute is present on the controller or action method the action filter code will not be executed.

Full source code here.

Altering the ASP.NET MVC model with an ActionFilter

Action filters are executed before and/or after the execution of an action method, they can be used to modify how an action executes or to perform a separate task, such as authorization or logging.

Action filters can be applied globally, at the controller level, or on an action method.

See here for more details.

In this post I’ll deal with how action filters allow you intercept an outgoing response to change a value in the returned model.

Action filter

Create a filter that inherits from ActionFilterAttribute and override the OnActionExecuted method.

public override void OnActionExecuted(ActionExecutedContext filterContext)

From the filterContext we can get model.

var model = filterContext.Controller.ViewData.Model as BaseModel;

Any value in the BaseModel can now be changed, in the example provided I change the MeetingDate property.

This action filter to needs to be applied to the appropriate action methods.
I’m going to register the filter globally, in this way it will run on all executed action methods.

Go to the FilterConfig class to register the filter.

public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
	filters.Add(new HandleErrorAttribute());
	filters.Add(new ModelAlterFilterAttribute());
}

That is all you need to do to create an action filter, register it and to alter the returned model.

As an aside, if you want to alter the value of an incoming parameter you override the OnActionExecuting method of the action filter.
In this example customerID is just an int but this approach will work for complex models too.

public override void OnActionExecuting(ActionExecutingContext filterContext)
{
	var actionParams = filterContext.ActionParameters;

	object customerID;
	actionParams.TryGetValue("customerid", out customerID);
	if (customerID != null)
	{
		customerID = 222;
	}

	base.OnActionExecuting(filterContext);
}

In the next post I show how you to selectively disable a global action filter on specific action methods or controllers.

Full source code here.