Make sure we deduplicate LinkedChildren

4 files changed, 33 insertions, 8 deletions

diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs
index 20df42583d..3ba6750045 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs
@@ -1553,7 +1553,13 @@ public sealed class BaseItemRepository
                         }
                     }
 
-                    var childIdsToCheck = resolvedChildren.Select(c => c.ChildId).Distinct().ToList();
+                    // Deduplicate by ChildId, keeping the last occurrence (for playlist ordering)
+                    resolvedChildren = resolvedChildren
+                        .GroupBy(c => c.ChildId)
+                        .Select(g => g.Last())
+                        .ToList();
+
+                    var childIdsToCheck = resolvedChildren.Select(c => c.ChildId).ToList();
                     var existingChildIds = childIdsToCheck.Count > 0
                         ? context.BaseItems
                             .Where(e => childIdsToCheck.Contains(e.Id))
@@ -1646,8 +1652,14 @@ public sealed class BaseItemRepository
                     }
                 }
 
+                // Deduplicate by ChildId, keeping the last occurrence
+                newLinkedChildren = newLinkedChildren
+                    .GroupBy(c => c.ChildId)
+                    .Select(g => g.Last())
+                    .ToList();
+
                 // Validate that all child items exist
-                var childIdsToCheck = newLinkedChildren.Select(c => c.ChildId).Distinct().ToList();
+                var childIdsToCheck = newLinkedChildren.Select(c => c.ChildId).ToList();
                 var existingChildIds = childIdsToCheck.Count > 0
                     ? context.BaseItems
                         .Where(e => childIdsToCheck.Contains(e.Id))
diff --git a/Jellyfin.Server/Migrations/Routines/RemoveDuplicatePlaylistChildren.cs b/Jellyfin.Server/Migrations/Routines/RemoveDuplicatePlaylistChildren.cs
index 23f212424b..1545ebdc8e 100644
--- a/Jellyfin.Server/Migrations/Routines/RemoveDuplicatePlaylistChildren.cs
+++ b/Jellyfin.Server/Migrations/Routines/RemoveDuplicatePlaylistChildren.cs
@@ -45,10 +45,13 @@ internal class RemoveDuplicatePlaylistChildren : IMigrationRoutine
                 var linkedChildren = playlist.LinkedChildren;
                 if (linkedChildren.Length > 0)
                 {
-                    var nullItemChildren = linkedChildren.Where(c => c.ItemId is null);
-                    var deduplicatedChildren = linkedChildren.DistinctBy(c => c.ItemId);
-                    var newLinkedChildren = nullItemChildren.Concat(deduplicatedChildren);
-                    playlist.LinkedChildren = linkedChildren;
+                    var newLinkedChildren = linkedChildren
+                        .Where(c => c.ItemId is null || c.ItemId.Value.Equals(Guid.Empty))
+                        .Concat(linkedChildren
+                            .Where(c => c.ItemId.HasValue && !c.ItemId.Value.Equals(Guid.Empty))
+                            .DistinctBy(c => c.ItemId))
+                        .ToArray();
+                    playlist.LinkedChildren = newLinkedChildren;
                     playlist.UpdateToRepositoryAsync(ItemUpdateType.MetadataEdit, CancellationToken.None).GetAwaiter().GetResult();
                     _playlistManager.SavePlaylistFile(playlist);
                 }
diff --git a/MediaBrowser.Providers/BoxSets/BoxSetMetadataService.cs b/MediaBrowser.Providers/BoxSets/BoxSetMetadataService.cs
index bdc5b5df29..3a872f687c 100644
--- a/MediaBrowser.Providers/BoxSets/BoxSetMetadataService.cs
+++ b/MediaBrowser.Providers/BoxSets/BoxSetMetadataService.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using MediaBrowser.Controller.Configuration;
@@ -70,7 +71,11 @@ public class BoxSetMetadataService : MetadataService<BoxSet, BoxSetInfo>
         if (mergeMetadataSettings)
         {
             // TODO: Change to only replace when currently empty or requested. This is currently not done because the metadata service is not handling attaching collection items based on the provider responses
-            targetItem.LinkedChildren = sourceItem.LinkedChildren.Concat(targetItem.LinkedChildren).DistinctBy(i => i.ItemId).ToArray();
+#pragma warning disable CS0618 // Type or member is obsolete - fallback for legacy path-based dedup
+            targetItem.LinkedChildren = sourceItem.LinkedChildren.Concat(targetItem.LinkedChildren)
+                .DistinctBy(i => i.ItemId.HasValue && !i.ItemId.Value.Equals(Guid.Empty) ? i.ItemId.Value.ToString() : i.Path ?? string.Empty)
+                .ToArray();
+#pragma warning restore CS0618
         }
     }
 
diff --git a/MediaBrowser.Providers/Playlists/PlaylistMetadataService.cs b/MediaBrowser.Providers/Playlists/PlaylistMetadataService.cs
index 45b61319b7..429830c70c 100644
--- a/MediaBrowser.Providers/Playlists/PlaylistMetadataService.cs
+++ b/MediaBrowser.Providers/Playlists/PlaylistMetadataService.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using MediaBrowser.Controller.Configuration;
@@ -72,7 +73,11 @@ public class PlaylistMetadataService : MetadataService<Playlist, ItemLookupInfo>
             }
             else
             {
-                targetItem.LinkedChildren = sourceItem.LinkedChildren.Concat(targetItem.LinkedChildren).DistinctBy(i => i.ItemId).ToArray();
+#pragma warning disable CS0618 // Type or member is obsolete - fallback for legacy path-based dedup
+                targetItem.LinkedChildren = sourceItem.LinkedChildren.Concat(targetItem.LinkedChildren)
+                    .DistinctBy(i => i.ItemId.HasValue && !i.ItemId.Value.Equals(Guid.Empty) ? i.ItemId.Value.ToString() : i.Path ?? string.Empty)
+                    .ToArray();
+#pragma warning restore CS0618
             }
 
             if (replaceData || targetItem.Shares.Count == 0)