Warning before deleting a page that is used in a property decorated with a SelectOne or SelectMany attribute

Long title and I hope it made some sense.

The case is that it's quite common that the underlying data for SelectionFactories which is then used with SelectOne and SelectMany attributes is normal Episerver pages. For example this is used to handle contact-cards in the Alloy site.

But since it's pages there is always a risk that someone by mistake deletes such a page causing problems. We would really like to have Episervers built in is this page used somewhere check.

The fix for a SelectOne attribute is as easy as having the underlying property to be of type ContentReference instead of a string. But if you have a SelectMany the underlying property needs to be a string and the chosen values is just added as a comma separated string.

To fix this for SelectMany I have created a custom attribute and a validation attribute class. When you add a SelectMany attribute where the SelectionFactory returns ContentReferences as id's you also add the new custom attribute which specifies an IList<ContentReference> property. The validation attribute then adds / removes references to the IList property automatically. With this when we try to delete a referenced page we get the builtin reference check functionality.

Pseudo code:

SelectMany(typeof(factoryclass))
SelectManyListProperty("ListPropertyName")
public virtual string SelectManyProp { get; set; }

public virtual IList ListPropertyName {get; set;}

Before

After

Note that the ContentReference property isn't updated until page is published (values are there) and ofcourse it should be hidden under an other tab or atleast disabled for editors.

Code over at my Gist.