nuPickers data source to lookup values from a Nest Content property

XPathLookupDataSource.cs

using nuPickers.Shared.DotNetDataSource;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Umbraco.Core;
using Umbraco.Core.Models;
using Umbraco.Web;

namespace Outfield.Digital.DataSources
{
    public class XPathLookupDataSource : IDotNetDataSource
    {
        [DotNetDataSource(Title = "Node XPath", Description = "XPath to the node that holds the lookup property")]
        public string NodeXPath { get; set; }

        [DotNetDataSource(Title = "Lookup Property Alias", Description = "The alias of the lookup property")]
        public string LookupPropertyAlias { get; set; }

        [DotNetDataSource(Title = "Key Property Alias", Description = "The property alias of the property to use as the key")]
        public string KeyPropertyAlias { get; set; }

        [DotNetDataSource(Title = "Value Property Alias", Description = "The property alias of the property to use as the value")]
        public string ValuePropertyAlias { get; set; }

        public IEnumerable<KeyValuePair<string, string>> GetEditorDataItems(int contextId)
        {
            if (HttpContext.Current != null)
            {
                var xpath = NodeXPath ?? "$parent";
                var currentId = HttpContext.Current.Request.QueryString["currentId"];
                var parentId = HttpContext.Current.Request.QueryString["parentId"];
                var currentOrParentId = !currentId.IsNullOrWhiteSpace() && currentId != "0" ? currentId : parentId;

                var lookups = new Dictionary<string, string>()
                {
                    { "$current", string.Format("id({0})", currentId) },
                    { "$parent", string.Format("id({0})", parentId) },
                    { "$ancestorOrSelf", string.Format("id({0})", currentOrParentId) },
                    { "$site", string.Format("id({0})/ancestor-or-self::*[@level=1]", currentOrParentId) },
                    { "$root", "/root" },
                };

                foreach (var lookup in lookups)
                {
                    xpath = xpath.Replace(lookup.Key, lookup.Value);
                }

                var node = UmbracoContext.Current.ContentCache.GetSingleByXPath(xpath);
                if (node != null && node.HasValue(LookupPropertyAlias))
                {
                    var deps = node.GetPropertyValue<IEnumerable<IPublishedContent>>(LookupPropertyAlias);
                    if (deps != null && deps.Any())
                    {
                        return deps.ToDictionary(k => KeyPropertyAlias.InvariantEquals("key") ? k.GetKey().ToString() : k.GetPropertyValue<string>(KeyPropertyAlias),
                            v => ValuePropertyAlias.InvariantEquals("name") ? v.Name : v.GetPropertyValue<string>(ValuePropertyAlias));
                    }
                }
            }

            return new Dictionary<string, string>();
        }
    }
}