I'm trying to get Donut Caching working per page for some controls. I'm overriding the following method in the UmbracoApplication class:

public class ApplicationStartup : UmbracoApplication
    {
        public override string GetVaryByCustomString(HttpContext context, string custom)
        {
            switch (custom)
            {
                case "url":
                    return "url=" + context.Request.Url.AbsoluteUri;
            }

            return base.GetVaryByCustomString(context, custom);
        }
    }

On my action method I have the following:

[DonutOutputCache(CacheProfile = "CarouselItems", VaryByCustom = "url", VaryByParam = "*")]
        [ChildActionOnly]
        public ActionResult GetCarouselItems()
        {
            CarouselHelper helper = new CarouselHelper();
            HeaderCarouselViewModel headerCarouselViewModel = helper.GetCarouselItems(this.CurrentPage);

            return PartialView("Components/_Carousel", headerCarouselViewModel);
        }

And finally I have the following cache profile:

<caching>
      <outputCacheSettings>
        <outputCacheProfiles>
          <add name="CarouselItems" duration="10" varyByCustom="url" varyByParam="*" />
        </outputCacheProfiles>
      </outputCacheSettings>
    </caching>

But, it never hits my GetVaryByCustomString method. Has anyone managed to get Donut Caching working on 7.4.1?

Greg.