Prevent page error when Datasource is missing after Upgrade

If you have upgraded Sitecore and along with it GlassMapper to version 5 there might be an issue when the Datasource item is not available in the target database, which will throw an error and the page will not load. Prior to the upgrade this would not have been an issue and the invalid Datasource was simply ignored. When this happens you will see an error in the log like this:

Exception: System.InvalidOperationException 
Message: The model item passed into the dictionary is of type 'Sitecore.Mvc.Presentation.RenderingModel', but this dictionary requires a model item of type 'DatasourceNamespace.DatasourceType'.
Source: System.Web.Mvc
   at System.Web.Mvc.ViewDataDictionary`1.SetModel(Object value)
   at System.Web.Mvc.ViewDataDictionary..ctor(ViewDataDictionary dictionary)
   at System.Web.Mvc.WebViewPage`1.SetViewData(ViewDataDictionary viewData)
   at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
   at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData)
   at Sitecore.Mvc.Presentation.ViewRenderer.Render(TextWriter writer) 


This can be fixed by checking if the Datasource exists and clearing it in case it doesn’t. The RenderRendering processor is a good place to insert this logic:

using Sitecore.Mvc.Pipelines.Response.RenderRendering; 

namespace Custom.Pipelines.RenderRendering
    public class ClearInvalidDatasource : RenderRenderingProcessor
        public override void Process(RenderRenderingArgs args)
            var rendering = args.Rendering;

            if (!string.IsNullOrWhiteSpace(rendering.DataSource) && Sitecore.Context.Database.Items.GetItem(rendering.DataSource) == null)
                rendering.DataSource = string.Empty;

This customization can be enabled with the following patch file:

<configuration xmlns:patch=""> 
        <processor patch:before="*[@type='Sitecore.Mvc.Pipelines.Response.RenderRendering.EnterRenderingContext, Sitecore.Mvc']" type="Custom.Pipelines.RenderRendering.ClearInvalidDatasource, Project.Common" />

Now that this change is in place the behavior will be identical to the behavior prior to the upgrade.

Fix Custom Cache after Sitecore upgrade

Sitecore allows you to create custom caches which can be managed just like all other Sitecore caches. Brian Caos wrote a great blog post about this which can be found here. Recently Sitecore has made some changes to this and if you are upgrading Sitecore you will notice that the code will not compile anymore. For example below code:

 Cache cache = CacheManager.FindCacheByName(cacheName);

will now throw a compile error:

Error CS0411 The type arguments for method 'CacheManager.FindCacheByName<T>(string)' cannot be inferred from the usage. Try specifying the type arguments explicitly. 

Furthermore this now returns an object of type Sitecore.Caching.Generics.ICache<TKey>. My first attempt at fixing this was by just passing the type of my custom cache in the generic which fixes the compile error but now the code throws an exception at runtime:

Exception: System.InvalidCastException 
Message: Unable to cast object of type 'Sitecore.Caching.Cache' to type 'Sitecore.Caching.Generics.ICache`1[MyCustomCache]'.
Source: Sitecore.Kernel
   at Sitecore.Caching.DefaultCacheManager.FindCacheByName[TKey](String name)

The generic now needs the type of the key passed in. In most cases this can just be set to string. To fix this code changes will be required in 2 places.

1. Custom cache object

In the custom cache make sure the base object uses Sitecore.Caching.Generics and also specify string as the key e.g:

 //updated from Sitecore.Caching
using Sitecore.Caching.Generics;

//Specify the generic type of the key
public class MyCustomCache : CustomCache<string> 

2. Custom Cache Clearer

In the method which clears the cache make sure to also pass the same generic for the key, see highlighted line:

private void DoClear()
    foreach (string cacheName in Caches)
        //update to pass generic
        Cache cache = CacheManager.FindCacheByName<string>(cacheName); 
        if (cache == null)
        Log.Info(this + ". Clearing " + cache.Count + " items from " + cacheName, this);