Restrict Item by Base Template on a Field IncludeTemplatesForSelection

Question

Out of the box it is possible to restrict items in a fields data source by its base template type. I can specify a filter as follows that restricts to items of type Employee...

DataSource=/sitecore/content/home/people/employees&IncludeTemplatesForSelection=Employee

If Employee uses Person as its base template, I'd like to specify something like this...

DataSource=/sitecore/content/home/people&IncludeBaseTemplatesForSelection=Person

That would allow me to select any item that has Person as its base template (so allow I could select Person and Employee items, or any other item that derives from Person base template.).

Is this possible?

Answer 1

I've had to do something similar recently which involved extending the treeview and used JammyKams post as a guide so thought I'd have a go at putting something together for this:

public class TreelistWithChildTemplateSupport : TreeList
{

    [Description("Base templates to include.")]
    [Category("Data")]
    public string IncludeBaseTemplatesForSelection
    {
        get { return GetViewStateString("IncludeBaseTemplatesForSelection"); }
        set
        {
            Assert.ArgumentNotNull(value, "value");
            SetViewStateString("IncludeBaseTemplatesForSelection", value);
        }
    }

    public new virtual void Add()
    {
    if (!this.HasIncludeBaseTemplatesForSelection(selectionItem))
      return;
    base.Add();
   }

  private bool HasIncludeBaseTemplatesForSelection(Item item)
  {
  Assert.ArgumentNotNull((object) item, "item");
  if (this.IncludeBaseTemplatesForSelection.Length == 0)
    return true;
  return HasItemBaseTemplate(item, this.IncludeBaseTemplatesForSelection);
 }
}

Then in the HasItemBaseTemplate() you could do something similar to Anders post here: https://laubplusco.net/sitecore-extensions-does-a-sitecore-item-derive-from-a-template/

I've not tested this code but hopefully this is a good start for you.