Sitecore Publish Cache Dependency

From time to time we all run into situations where we want to use caching to store data and when working with Sitecore a lot of those situations also involves data originating from items. But what happens when those items change?

I have seen a lot of examples where the cache was set to expire after a period of time and the editors were told that when they make changes it will take up to xx minutes before the changes take effect.

Wouldn’t it be great if the cache was cleared when a publish was performed in Sitecore? Well if you use the CacheMonitor listed below it can.

using System;
using System.Runtime.Caching;

namespace TheGrumpyCoder
{
  public sealed class PublishChangeMonitor : ChangeMonitor
  {
    public PublishChangeMonitor()
    {
      Boolean initializationComplete = false;

      try
      {
        _uniqueId = Guid.NewGuid().ToString();
        Sitecore.Events.Event.Subscribe("publish:end", PublishCacheDependency_OnPublishEnd);
        Sitecore.Events.Event.Subscribe("publish:end:remote", PublishCacheDependency_OnPublishEnd);
        initializationComplete = true;
      }
      finally
      {
        InitializationComplete();

        if (!initializationComplete)
          Dispose(true);
      }
      InitializationComplete();
    }

    public void PublishCacheDependency_OnPublishEnd(object sender, EventArgs eventArgs)
    {
      OnChanged(null);
    }

    protected override void Dispose(Boolean disposing)
    {
      Sitecore.Events.Event.Unsubscribe("publish:end", PublishCacheDependency_OnPublishEnd);
      Sitecore.Events.Event.Unsubscribe("publish:end:remote", PublishCacheDependency_OnPublishEnd);
    }

    public override String UniqueId
    {
      get { return _uniqueId; }
    }

    private readonly String _uniqueId;
  }
}

This CacheMonitor will listen to Sitecores event queue and whenever a publish:end or publish:end:remote event is fired the CacheMonitor callback PublishCacheDependency_OnPublishEnd is called which in turn triggers the OnChanged method on the ChangeMonitor.

Using it couldn’t be easier. Just create a CacheItemPolicy and hook it up with the PublishChangeMonitor and use it when adding your data to the cache and you are all hooked up.

using System.Runtime.Caching;

CacheItemPolicy cacheItemPolicy = new CacheItemPolicy
{
  AbsoluteExpiration = DateTime.Now.AddHours(1)
};
cacheItemPolicy.ChangeMonitors.Add(new PublishChangeMonitor());

MemoryCache.Default.Add(key, data, cacheItemPolicy);