Prototype for an Umbraco "XPath DropDownList" property editor.

XPathDropDownListPropertyEditor.cs

using System.Collections.Generic;
using System.Linq;
using Umbraco.Core;
using Umbraco.Core.Models;
using Umbraco.Core.PropertyEditors;
using Umbraco.Core.Xml;

namespace Umbraco.Web.PropertyEditors
{
	[PropertyEditor(Constants.PropertyEditors.XPathDropDownListAlias, "XPath DropDownList", "dropdown", ValueType = "INT")]
	public class XPathDropDownListPropertyEditor : DropDownWithKeysPropertyEditor
	{
		public override IDictionary<string, object> DefaultPreValues
		{
			get { return new Dictionary<string, object> { { "xpath", "//*[@isDoc]" } }; }
		}

		protected override PreValueEditor CreatePreValueEditor()
		{
			return new XPathDropDownListPreValueEditor();
		}

		internal class XPathDropDownListPreValueEditor : PreValueEditor
		{
			public XPathDropDownListPreValueEditor()
			{
				Fields.Add(new PreValueField
				{
					Key = "xpath",
					Name = "XPath",
					View = "textstring",
					Description = "You can use the tokens `$ancestorOrSelf` and `$currentPage`",
					HideLabel = false
				});
			}

			public override IDictionary<string, object> ConvertDbToEditor(IDictionary<string, object> defaultPreVals, PreValueCollection persistedPreVals)
			{
				var config = base.ConvertDbToEditor(defaultPreVals, persistedPreVals);

				var xpath = config.ContainsKey("xpath") ? config["xpath"].ToString() : string.Empty;
				var vars = new[]
				{
					new XPathVariable("ancestorOrSelf", ""), // [LK] What to do here?
					new XPathVariable("currentPage", "") // [LK] What to do here?
				};

				var helper = new UmbracoHelper(UmbracoContext.Current);
				var items = helper.TypedContentAtXPath(xpath, vars);
				if (items != null)
					config.Add("items", items.ToDictionary(x => x.Id, x => x.Name));

				return config;
			}
		}
	}
}

The specific part that I am looking for advice on... is overriding the ConvertDbToEditor method the best way to pre-populate the list of items?