Working with the Output Cache and other Action Filters

Question

I have added Output Caching to a couple of actions in my app for some easy performance boosts. However, these actions also need to increment a counter after each request (it's a views counter) by hitting a Redis db.

At first, I figured I could just adjust the order in which the action filters execute to ensure the view is counted:

public class CountersAttribute : ActionFilterAttribute
{
    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        //increment my counter all clever like
        base.OnResultExecuted(filterContext);
    }
}

But that didn't work; apparently the OutputCacheAttribute doesn't behave like a normal action filter. Then I tried implementing a custom output cache:

public class OutputCacheWithCountersAttribute : OutputCacheAttribute
{
    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        //straight to the source to get my headcount!
        base.OnResultExecuted(filterContext);
    }
}

Nope, didn't work either; action filters appear to be entirely ignored once an action is cached. Bummer.

So, uh, is there any way (without implementing a custom output caching provider) for me to ensure my views are counted properly that is clean and sensible?

Answer 1

The OutputCacheAttribute has limitations by the way and there is a custom attribute named DonutOutputCache developed by Paul Hiles helps to overcome the limitations.

One of the important feature it supports is you can have an action filter that can be called all the times even the action is marked with cache attribute or not.

For ex. you want to cache an action for the duration 5 seconds and at the same time you want to log every time the action receives a request using a LogThis filter you can achieve that simply by below,

[LogThis]
[DonutOutputCache(Duration=5, Order=100)]
public ActionResult Index()

From Paul,

Yes, unlike the built-in OutputCacheAttribute, the action filters will execute even when a page is retrieved from the cache. The only caveat to add is that you do need to be careful about the filter order. If your action filter implements OnResultExecuting or OnResultExecuted then these methods will be executed in all cases, but for OnActionExecuting and OnActionExecuted, they will only be executed if the filter runs before the DonutOutputCacheAttribute. This is due to the way that MVC prevents subsequent filters from executing when you set the filterContext.Result property which is what we need to do for output caching.

I do not think that you can rely on the order in which action filters are defined on an action or controller. To ensure that one filter runs before another, you can make use of the Order property that is present on all ActionFilterAttribute implementations. Any actions without the order property set, default to an value of -1, meaning that they will execute before filters which have an explicit Order value.

Therefore, in your case, you can just add Order=100 to the DonutOutputCache attribute and all other filters will execute before the caching filter.