Skip to main content

Null Explosion Prevention with Datasources!

Sometimes bad data can sneak into the smallest of things and wreak havoc on a site bringing up a dreaded error page (hopefully captured and prettified). We’re going to cover two examples of sneaky bad data blowing up a component and how we can address the problem.

The scenario here revolves around an invalid datasource and a component making use of Glass - this bad data can come about from a publishing issue (such as publishing the page which references a datasource that hasn’t been published or wasn’t in the final workflow step to allow publishing), or some other kind of issue (an invalid item ID, a deleted item still being referenced etc).

1. Getting the Item
In the code for our rendering, we want to grab that datasource item to help out our model, so we did the following:

This confirms that the Guid is a valid format - but doesn’t confirm that it’s a valid item in the database before we pass it to GetItem to grab and cast to our Item_Type.
It wouldn't be unreasonable to expect GetItem to throw a null, which is exactly where I ran into trouble. Instead of returning a null, it blows up and you’ll never reach the next line.

To avoid this error remove references to GetItem<T>, confirm that your item exists, then use Cast<T> instead.
For example:


2. View Rendering Issue
In our same scenario we can come across another issue with the use of View Renderings - this view rendering has a datasource passed to it (instead of using the context item).
For example:
The usual expectation is that the model would return null if we had some kind of issue with the datasource. However, in this situation the bad datasource will blow the rendering up before ever trying to check that If Statement.

The problem isn’t with the view rendering, but getting the rendering within the pipeline. Sitecore will check to see if there’s a value (Sitecore.Mvc.Pipelines.Response.GetRenderer)  and send it back. So, if the datasource is set but wrong, instead of returning null it just sends back the bad data. It attempts to use the default model and promptly blows up - expecting a different model that’s never properly sent.

To fix this, we can override GetViewRenderer with a custom pipeline- modified from this thread:
https://github.com/mikeedwards83/Glass.Mapper/issues/163

This will prevent your view renderings from blowing up from a busted datasource as long as you have the regular null checking on the model set up!

Comments

  1. This comment has been removed by a blog administrator.

    ReplyDelete
  2. This comment has been removed by a blog administrator.

    ReplyDelete
  3. This comment has been removed by a blog administrator.

    ReplyDelete

Post a Comment

Popular posts from this blog

Using the Source Property

For each of the properties in your template you can set a source for it, this isn’t always used but can improve user experience drastically when done throughout a site. The source field comes in to play whenever you are using any of the following fields: Droplink, Droplist, Droptree, File, Grouped Droplink, Grouped Droplist, Image, Multilist, Treelist, Rich text field and a number of others. There are various ways of setting these up to achieve different results – but in general you are using the source to limit the set of items that can be used, and this requirement can also help you determine what kind of field to use. For example, if you have a Set of items all split down into sub folders and want the content editor to make use of the tree, you could use a TreeList or Drop Tree, but if you just want a set of items without the opportunity to see where those items are – multilists or droplinks are the way to go. For Images you’re generally just specifying where to look for and put th

Determining Page Editor Status with Javascript

     Often you’ll need to know if you are inside or outside the Experience/Page Editor in order perform an action. If you are on the server-side in code-behind you can check the Sitecore.Context.PageMode to determine which mode you are in. But what about at runtime? Javascript per usual can save the day! Though you can find PageModes through the Sitecore object if it is available to the browser, it may not be there. Depending on how things have been set up with your solution, the Sitecore object may not return a null as would be expected when checking to see if you can access it. Instead Sitecore may be undefined.  Contrary to some examples on the web with only null checks, this quick little change in your script can correctly let you know if you are in the page editor: Just take a look to see if isPageEditor is true or false and you’re set!

Links as Items Redux!

Previously I had posted on how to set up items in your content tree to act as external links to other pages (for use with Navigation mainly – for example if you have a blog elsewhere but still want it listed in the main navigation). However, Ivan Buzyka pointed out some issues with the simple implementation so I added creating a better redirect to my ‘to do’ list for the blog. The time has come! Let’s pretend we are modifying an existing site, we don’t want to change the navigation so that won’t be covered here – we just want to update our layout to work a little more universally. Our new items need to be able to link to an internal, external or Media item reliably for display in our navigation. Our template will consist of similar things to last time: Link: General Link Nav Title: Text -> standard values: $name In Navigation: Checkbox ->standard values: checked Create the template, add in standard values for it with the above settings and now we can create our Layout which shou