Fix AdjacentTo being ignored on non-recursive item queries

5 files changed, 58 insertions, 49 deletions

diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs
index a4de9feb05..54926b7cd9 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs
@@ -35,11 +35,40 @@ public sealed partial class BaseItemRepository
     {
         dbQuery = TranslateQuery(dbQuery, context, filter);
         dbQuery = ApplyGroupingFilter(context, dbQuery, filter);
+        dbQuery = ApplyAdjacencyFilter(context, dbQuery, filter);
         dbQuery = ApplyQueryPaging(dbQuery, filter);
         dbQuery = ApplyNavigations(dbQuery, filter);
         return dbQuery;
     }
 
+    /// <summary>
+    /// Trims an ordered query down to the AdjacentTo item and its immediate neighbours.
+    /// </summary>
+    private IQueryable<BaseItemEntity> ApplyAdjacencyFilter(JellyfinDbContext context, IQueryable<BaseItemEntity> dbQuery, InternalItemsQuery filter)
+    {
+        if (filter.AdjacentTo.IsNullOrEmpty())
+        {
+            return dbQuery;
+        }
+
+        // Adjacency is relative to the result set and the order the query asked for, so the ids have
+        // to be read back in that order.
+        var orderedIds = dbQuery.Select(e => e.Id).ToList();
+        var index = orderedIds.IndexOf(filter.AdjacentTo.Value);
+        if (index < 0)
+        {
+            // The item isn't part of this result set, so it has no neighbours in it either.
+            return dbQuery.Take(0);
+        }
+
+        var start = Math.Max(index - 1, 0);
+        var adjacentIds = orderedIds.GetRange(start, Math.Min(index + 2, orderedIds.Count) - start);
+
+        var adjacentQuery = context.BaseItems.AsNoTracking().AsSingleQuery().Where(e => adjacentIds.Contains(e.Id));
+
+        return ApplyOrder(adjacentQuery, filter, context);
+    }
+
     private IQueryable<BaseItemEntity> ApplyQueryPaging(IQueryable<BaseItemEntity> dbQuery, InternalItemsQuery filter)
     {
         if (filter.Limit.HasValue || filter.StartIndex.HasValue)
diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.Querying.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.Querying.cs
index 1ff8d8f863..b02d91b458 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.Querying.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.Querying.cs
@@ -49,6 +49,7 @@ public sealed partial class BaseItemRepository
 
         dbQuery = TranslateQuery(dbQuery, context, filter);
         dbQuery = ApplyGroupingFilter(context, dbQuery, filter);
+        dbQuery = ApplyAdjacencyFilter(context, dbQuery, filter);
 
         if (filter.EnableTotalRecordCount)
         {
@@ -75,6 +76,7 @@ public sealed partial class BaseItemRepository
         dbQuery = TranslateQuery(dbQuery, context, filter);
 
         dbQuery = ApplyGroupingFilter(context, dbQuery, filter);
+        dbQuery = ApplyAdjacencyFilter(context, dbQuery, filter);
         dbQuery = ApplyQueryPaging(dbQuery, filter);
 
         var hasRandomSort = filter.OrderBy.Any(e => e.OrderBy == ItemSortBy.Random);
diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs
index 47f8a40b9c..1b73087296 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs
@@ -1243,33 +1243,6 @@ public sealed partial class BaseItemRepository
             }
         }
 
-        if (filter.AdjacentTo.HasValue && !filter.AdjacentTo.Value.IsEmpty())
-        {
-            var adjacentToId = filter.AdjacentTo.Value;
-            var targetItem = context.BaseItems.Where(e => e.Id == adjacentToId).Select(e => new { e.SortName, e.Id }).FirstOrDefault();
-            if (targetItem is not null)
-            {
-                var targetSortName = targetItem.SortName ?? string.Empty;
-
-                // Fetch both prev and next adjacent items in a single query using Concat (UNION ALL).
-                var adjacentIds = context.BaseItems
-                    .Where(e => string.Compare(e.SortName, targetSortName) < 0)
-                    .OrderByDescending(e => e.SortName)
-                    .Select(e => e.Id)
-                    .Take(1)
-                    .Concat(
-                        context.BaseItems
-                            .Where(e => string.Compare(e.SortName, targetSortName) > 0)
-                            .OrderBy(e => e.SortName)
-                            .Select(e => e.Id)
-                            .Take(1))
-                    .ToList();
-
-                adjacentIds.Add(adjacentToId);
-                baseQuery = baseQuery.Where(e => adjacentIds.Contains(e.Id));
-            }
-        }
-
         return baseQuery;
     }
 }
diff --git a/MediaBrowser.Controller/Entities/Folder.cs b/MediaBrowser.Controller/Entities/Folder.cs
index b1f7f29bad..ed11f21f52 100644
--- a/MediaBrowser.Controller/Entities/Folder.cs
+++ b/MediaBrowser.Controller/Entities/Folder.cs
@@ -1085,15 +1085,7 @@ namespace MediaBrowser.Controller.Entities
                 items = ApplyNameFilter(items, query);
             }
 
-            var filteredItems = items as IReadOnlyList<BaseItem> ?? items.ToList();
-            var result = UserViewBuilder.SortAndPage(filteredItems, null, query, LibraryManager);
-
-            if (query.EnableTotalRecordCount)
-            {
-                result.TotalRecordCount = filteredItems.Count;
-            }
-
-            return result;
+            return UserViewBuilder.SortAndPage(items, null, query, LibraryManager);
         }
 
         private static IEnumerable<BaseItem> ApplyNameFilter(IEnumerable<BaseItem> items, InternalItemsQuery query)
diff --git a/MediaBrowser.Controller/Entities/UserViewBuilder.cs b/MediaBrowser.Controller/Entities/UserViewBuilder.cs
index 9ba103cc8b..fe7866fe65 100644
--- a/MediaBrowser.Controller/Entities/UserViewBuilder.cs
+++ b/MediaBrowser.Controller/Entities/UserViewBuilder.cs
@@ -490,6 +490,13 @@ namespace MediaBrowser.Controller.Entities
             }
 
             var itemsArray = totalRecordLimit.HasValue ? items.Take(totalRecordLimit.Value).ToArray() : items.ToArray();
+
+            // Adjacency is defined by the order the query asked for, so it has to run after sorting but before paging.
+            if (!query.AdjacentTo.IsNullOrEmpty())
+            {
+                itemsArray = FilterForAdjacency(itemsArray, query.AdjacentTo.Value).ToArray();
+            }
+
             var totalCount = itemsArray.Length;
 
             if (query.Limit.HasValue && query.Limit.Value > 0)
@@ -886,26 +893,32 @@ namespace MediaBrowser.Controller.Entities
             return _userViewManager.GetUserSubView(parent.Id, type, localizationKey, sortName);
         }
 
-        public static IEnumerable<BaseItem> FilterForAdjacency(List<BaseItem> list, Guid adjacentTo)
+        /// <summary>
+        /// Trims an ordered list down to the requested item and its immediate neighbours.
+        /// </summary>
+        /// <param name="list">The items in the order the query returned them.</param>
+        /// <param name="adjacentTo">The id of the item to return the neighbours of.</param>
+        /// <returns>The previous item, the requested item and the next item, in order.</returns>
+        public static IEnumerable<BaseItem> FilterForAdjacency(IReadOnlyList<BaseItem> list, Guid adjacentTo)
         {
-            var adjacentToItem = list.FirstOrDefault(i => i.Id.Equals(adjacentTo));
-
-            var index = list.IndexOf(adjacentToItem);
-
-            var previousId = Guid.Empty;
-            var nextId = Guid.Empty;
-
-            if (index > 0)
+            var index = -1;
+            for (var i = 0; i < list.Count; i++)
             {
-                previousId = list[index - 1].Id;
+                if (list[i].Id.Equals(adjacentTo))
+                {
+                    index = i;
+                    break;
+                }
             }
 
-            if (index < list.Count - 1)
+            // The item isn't part of this result set, so it has no neighbours in it either.
+            if (index < 0)
             {
-                nextId = list[index + 1].Id;
+                return [];
             }
 
-            return list.Where(i => i.Id.Equals(previousId) || i.Id.Equals(nextId) || i.Id.Equals(adjacentTo));
+            var start = Math.Max(index - 1, 0);
+            return list.Skip(start).Take(Math.Min(index + 2, list.Count) - start);
         }
     }
 }