Caching multiple output versions of pages: custom key variable

How about trying to leverage: GetVaryByCustomString event in application events ? In Kentico we override default Microsoft method and add in an event that allows you to hook onto it and inject extra variables.

Hi Michal,

Could you elaborate on that? I don't get the GetVaryByCustomString event to fire.

GetVaryByCustomString fires when application requests custom string key for output caching and we are adding to it via our own override:

// Get base value var result = base.GetVaryByCustomString(context, custom);

        var e = new GetVaryByCustomStringEventArgs
            {
                Context = context,
                Custom = custom,
                Result = result
            };

        return CMSApplication.GetVaryByCustomString(e);

Then we are using result of raised event in further processing of output in OutputHelper.GetVaryByCustomString.

So you could change it and override on your own it on application level in GlobalAsax and I am not sure whether this would not require a touch in customization of CacheHelper as well. Another approach would be following web.config key CMSOutputCacheItems where comma separate values can be entered, but that will not help with cookie based recognition as config is not dynamic enough.

Another suggestion, that I am thinking is to create custom Helper and override GetVaryByCustomString, but be careful, since this helper does a lot of heavy lifting and work to retrieve items properly.

Hi Michal,

I think I haven't been clear on the requirement:

Out of curiosity I set up a page with partial caching for a webpart - now the event is fired.

However, it is modifying keys for full page output caching I am interested in.

Is there a similar approach for this situation?

Thanks, Tobi

Hi Tobias,

I had found out another, better approach (though cache variables should still work). Anyway,

private void OutputFilter_SaveOutputToCache_Before(object sender, OutputCacheEventArgs e)
        {

string cacheKey = e.Output.CacheKey;

//var cookieKey = HttpContext.Current.Request.Cookies["cache"];

cacheKey = cacheKey + "|Test";

e.Output.CacheKey = cacheKey;
}

Will allow you to change cache keys with which item is stored. However, you will also have to connect to additional SendCacheOutput event where you are passed output variable by reference and you can use TryGetFromCacheInternal according to your custom keys.

Hope this works for you now.

Hi Michal,

I don't think that works either. The limitation is the SendCacheOutput: "Occurs only if the cached output is found...". Because the system checks only the default cache keys nothing is found for the manipulated key.

I found a solution which works for me by implementing custom CacheHelper and overriding GetInternal and InsertInternal Methods:

[assembly: RegisterCustomHelper(typeof(CustomCacheHelper))]
public class CustomCacheHelper : CacheHelper
{

    protected override object GetInternal(string key, bool useFullKey)
    {
        if(key.StartsWith("outputdata"))
        {
            string cookieValue = this.GetCustomCookieValue();
            if(!String.IsNullOrEmpty(cookieValue))
            {
                key += "|myKey=" + cookieValue;
            }           
        }
        return base.GetInternal(key, useFullKey);
    }

    protected override void InsertInternal(string key, object value, CMSCacheDependency dependencies, DateTime absoluteExpiration, TimeSpan slidingExpiration, CacheItemPriority priority, CacheItemRemovedCallback onRemoveCallback, bool useFullKey)
    {
        if (key.StartsWith("outputdata"))
        {
            string cookieValue = this.GetCustomCookieValue();
            if (!String.IsNullOrEmpty(cookieValue))
            {
                key += "|myKey=" + cookieValue;
            }
        }
        base.InsertInternal(key, value, dependencies, absoluteExpiration, slidingExpiration, priority, onRemoveCallback, useFullKey);
    }
}

I am not fully satisfied with the solution because of the direct key string manipulation, but nothing else seems to be working.

Still thank you Michal, your ideas put me on the right track.