ASP.NET MVC: Action Filter to set up controller variables?

Question

I have a scenario whereby with every page request I must check the session of the presence of a particular ID. If this is found I must grab a related object from the database an

Answer 1

Another way is to do that with Model Binders. Suppose that object is ShoppingCart

//Custom Model Binder
public class ShoppingCarModelBinder : IModelBinder
    {
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            //TODO: retrieve model or return null;
        }
    }
 //register that binder in global.asax in application start

ModelBinders.Binders.Add(typeof(ShoppingCart), new ShoppingCartBinder());

// controller action

public ActionResult DoStuff(ShoppingCart cart)
{
     if(cart == null)
     {
     //whatever you do when cart is null, redirect. etc
     }
     else
     {
     // do stuff with cart
     }
}

Moreover, this is more unit testable and clear way, as this way action relies on parameters supplied from outside