Correct the population of the parent for sibling items when retrieved under a folder (#20083)

Correct the population of the parent for sibling items when retrieved under a folder.

src/Umbraco.Cms.Api.Management/Controllers/Tree/EntityTreeControllerBase.cs

@@ -73,9 +73,7 @@ public abstract class EntityTreeControllerBase<TItem> : ManagementApiControllerB
         }
 
         IEntitySlim? entity = siblings.FirstOrDefault();
-        Guid? parentKey = entity?.ParentId > 0
-            ? EntityService.GetKey(entity.ParentId, ItemObjectType).Result
-            : Constants.System.RootKey;
+        Guid? parentKey = GetParentKey(entity);
 
         TItem[] treeItemViewModels = MapTreeItemViewModels(parentKey, siblings);
 
@@ -86,6 +84,14 @@ public abstract class EntityTreeControllerBase<TItem> : ManagementApiControllerB
         return Ok(result);
     }
 
+    /// <summary>
+    /// Gets the parent key for an entity, or root if null or no parent.
+    /// </summary>
+    protected virtual Guid? GetParentKey(IEntitySlim? entity) =>
+        entity?.ParentId > 0
+            ? EntityService.GetKey(entity.ParentId, ItemObjectType).Result
+            : Constants.System.RootKey;
+
     protected virtual async Task<ActionResult<IEnumerable<TItem>>> GetAncestors(Guid descendantKey, bool includeSelf = true)
     {
         IEntitySlim[] ancestorEntities = await GetAncestorEntitiesAsync(descendantKey, includeSelf);

src/Umbraco.Cms.Api.Management/Controllers/Tree/FolderTreeControllerBase.cs

@@ -45,6 +45,30 @@ public abstract class FolderTreeControllerBase<TItem> : NamedEntityTreeControlle
 
     protected abstract UmbracoObjectTypes FolderObjectType { get; }
 
+    /// <inheritdoc/>
+    protected override Guid? GetParentKey(IEntitySlim? entity)
+    {
+        if (entity is null || entity.ParentId <= 0)
+        {
+            return Constants.System.RootKey;
+        }
+
+        Attempt<Guid> getKeyAttempt = EntityService.GetKey(entity.ParentId, ItemObjectType);
+        if (getKeyAttempt.Success)
+        {
+            return getKeyAttempt.Result;
+        }
+
+        // Parent could be a folder, so try that too.
+        getKeyAttempt = EntityService.GetKey(entity.ParentId, FolderObjectType);
+        if (getKeyAttempt.Success)
+        {
+            return getKeyAttempt.Result;
+        }
+
+        return Constants.System.RootKey;
+    }
+
     protected void RenderFoldersOnly(bool foldersOnly) => _foldersOnly = foldersOnly;
 
     protected override IEntitySlim[] GetPagedRootEntities(int skip, int take, out long totalItems)