Translate member picker property editor value to V14 compatible format (and back again) (#16149)

* Translate member picker property editor value to V14 compatible format (and back again)

* Fix typo

---------

Co-authored-by: Elitsa <elm@umbraco.dk>

src/Umbraco.Core/PropertyEditors/MemberPickerPropertyEditor.cs

@@ -1,3 +1,11 @@
+using Umbraco.Cms.Core.IO;
+using Umbraco.Cms.Core.Models;
+using Umbraco.Cms.Core.Models.Editors;
+using Umbraco.Cms.Core.Serialization;
+using Umbraco.Cms.Core.Services;
+using Umbraco.Cms.Core.Strings;
+using Umbraco.Extensions;
+
 namespace Umbraco.Cms.Core.PropertyEditors;
 
 [DataEditor(
@@ -9,4 +17,49 @@ public class MemberPickerPropertyEditor : DataEditor
     public MemberPickerPropertyEditor(IDataValueEditorFactory dataValueEditorFactory)
         : base(dataValueEditorFactory)
         => SupportsReadOnly = true;
+
+    protected override IDataValueEditor CreateValueEditor() =>
+        DataValueEditorFactory.Create<MemberPickerPropertyValueEditor>(Attribute!);
+
+    private class MemberPickerPropertyValueEditor : DataValueEditor
+    {
+        private readonly IMemberService _memberService;
+
+        public MemberPickerPropertyValueEditor(
+            IShortStringHelper shortStringHelper,
+            IJsonSerializer jsonSerializer,
+            IIOHelper ioHelper,
+            DataEditorAttribute attribute,
+            IMemberService memberService)
+            : base(shortStringHelper, jsonSerializer, ioHelper, attribute)
+            => _memberService = memberService;
+
+        public override object? ToEditor(IProperty property, string? culture = null, string? segment = null)
+        {
+            // the stored value is either an UDI or an integer ID - need to transform this into the corresponding member key
+            var value = base.ToEditor(property, culture, segment);
+            if (value is not string stringValue || stringValue.IsNullOrWhiteSpace())
+            {
+                return value;
+            }
+
+            if (UdiParser.TryParse<GuidUdi>(stringValue, out GuidUdi? guidUdi))
+            {
+                return guidUdi.Guid;
+            }
+
+            if (int.TryParse(stringValue, out int memberId))
+            {
+                return _memberService.GetById(memberId)?.Key;
+            }
+
+            return null;
+        }
+
+        // the editor value is expected to be the member key - store it as the member UDI
+        public override object? FromEditor(ContentPropertyData editorValue, object? currentValue)
+            => editorValue.Value is string stringValue && Guid.TryParse(stringValue, out Guid memberKey)
+                ? new GuidUdi(Constants.UdiEntityType.Member, memberKey)
+                : null;
+    }
 }