Complete LinkedChildren integration and batch DTO optimizations

This commit integrates remaining performance changes:

- Add batch user data fetching in DtoService to reduce N+1 queries
- Add GetNextUpEpisodesBatch in TVSeriesManager for efficient batch retrieval
- Update Video/Movie/BoxSet to use LibraryManager for alternate versions
- Transition LinkedChild to use ItemId instead of Path (obsolete Path/LibraryItemId)
- Update providers and controllers for LinkedChildren-based references
- Add NextUpEpisodeBatchResult for batched episode queries
- Integrate IDescendantQueryProvider in SqliteDatabaseProvider

1 files changed, 20 insertions, 3 deletions

diff --git a/MediaBrowser.Controller/Entities/LinkedChildComparer.cs b/MediaBrowser.Controller/Entities/LinkedChildComparer.cs
index 4f13ac61fe..8b611345f4 100644
--- a/MediaBrowser.Controller/Entities/LinkedChildComparer.cs
+++ b/MediaBrowser.Controller/Entities/LinkedChildComparer.cs
@@ -19,17 +19,34 @@ namespace MediaBrowser.Controller.Entities
 
         public bool Equals(LinkedChild x, LinkedChild y)
         {
-            if (x.Type == y.Type)
+            if (x.Type != y.Type)
             {
-                return _fileSystem.AreEqual(x.Path, y.Path);
+                return false;
             }
 
-            return false;
+            // Compare by ItemId first (preferred)
+            if (x.ItemId.HasValue && y.ItemId.HasValue)
+            {
+                return x.ItemId.Value.Equals(y.ItemId.Value);
+            }
+
+#pragma warning disable CS0618 // Type or member is obsolete - fallback for shortcut/legacy comparison
+            // Fall back to Path comparison for shortcuts and legacy data
+            return _fileSystem.AreEqual(x.Path, y.Path);
+#pragma warning restore CS0618
         }
 
         public int GetHashCode(LinkedChild obj)
         {
+            // Use ItemId for hash if available, otherwise fall back to legacy fields
+            if (obj.ItemId.HasValue && !obj.ItemId.Value.Equals(Guid.Empty))
+            {
+                return HashCode.Combine(obj.ItemId.Value, obj.Type);
+            }
+
+#pragma warning disable CS0618 // Type or member is obsolete - fallback for shortcut/legacy hashing
             return ((obj.Path ?? string.Empty) + (obj.LibraryItemId ?? string.Empty) + obj.Type).GetHashCode(StringComparison.Ordinal);
+#pragma warning restore CS0618
         }
     }
 }