Don't use raw SQL

src/Jellyfin.Database/Jellyfin.Database.Implementations/DescendantQueryHelper.cs

@@ -0,0 +1,161 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.MatchCriteria;
+
+namespace Jellyfin.Database.Implementations;
+
+/// <summary>
+/// Provides methods for querying item hierarchies using iterative traversal.
+/// Uses AncestorIds and LinkedChildren tables for parent-child traversal.
+/// </summary>
+public static class DescendantQueryHelper
+{
+    /// <summary>
+    /// Gets a queryable of all descendant IDs for a parent item.
+    /// Traverses AncestorIds and LinkedChildren to find all descendants.
+    /// </summary>
+    /// <param name="context">Database context.</param>
+    /// <param name="parentId">Parent item ID.</param>
+    /// <returns>Queryable of descendant item IDs.</returns>
+    public static IQueryable<Guid> GetAllDescendantIds(JellyfinDbContext context, Guid parentId)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+
+        var descendants = TraverseHierarchyDown(context, [parentId]);
+
+        descendants.Remove(parentId);
+
+        return descendants.AsQueryable();
+    }
+
+    /// <summary>
+    /// Gets a queryable of all folder IDs that have any descendant matching the specified criteria.
+    /// Can be used in LINQ .Contains() expressions.
+    /// </summary>
+    /// <param name="context">Database context.</param>
+    /// <param name="criteria">The matching criteria to apply.</param>
+    /// <returns>Queryable of folder IDs.</returns>
+    public static IQueryable<Guid> GetFolderIdsMatching(JellyfinDbContext context, FolderMatchCriteria criteria)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+        ArgumentNullException.ThrowIfNull(criteria);
+        var matchingItemIds = criteria switch
+        {
+            HasSubtitles => context.MediaStreamInfos
+                .Where(ms => ms.StreamType == MediaStreamTypeEntity.Subtitle)
+                .Select(ms => ms.ItemId)
+                .Distinct()
+                .ToHashSet(),
+            HasChapterImages => context.Chapters
+                .Where(c => c.ImagePath != null)
+                .Select(c => c.ItemId)
+                .Distinct()
+                .ToHashSet(),
+            HasMediaStreamType m => GetMatchingMediaStreamItemIds(context, m),
+            _ => throw new ArgumentOutOfRangeException(nameof(criteria), $"Unknown criteria type: {criteria.GetType().Name}")
+        };
+
+        var ancestors = TraverseHierarchyUp(context, matchingItemIds);
+
+        return ancestors.AsQueryable();
+    }
+
+    private static HashSet<Guid> GetMatchingMediaStreamItemIds(JellyfinDbContext context, HasMediaStreamType criteria)
+    {
+        var query = context.MediaStreamInfos
+            .Where(ms => ms.StreamType == criteria.StreamType && ms.Language == criteria.Language);
+
+        if (criteria.IsExternal.HasValue)
+        {
+            var isExternal = criteria.IsExternal.Value;
+            query = query.Where(ms => ms.IsExternal == isExternal);
+        }
+
+        return query.Select(ms => ms.ItemId).Distinct().ToHashSet();
+    }
+
+    /// <summary>
+    /// Traverses DOWN the hierarchy from parent folders to find all descendants.
+    /// </summary>
+    private static HashSet<Guid> TraverseHierarchyDown(JellyfinDbContext context, ICollection<Guid> startIds)
+    {
+        var visited = new HashSet<Guid>(startIds);
+        var folderStack = new HashSet<Guid>(startIds);
+
+        while (folderStack.Count != 0)
+        {
+            var currentFolders = folderStack.ToArray();
+            folderStack.Clear();
+
+            var directChildren = context.AncestorIds
+                .WhereOneOrMany(currentFolders, e => e.ParentItemId)
+                .Select(e => e.ItemId)
+                .ToArray();
+
+            var linkedChildren = context.LinkedChildren
+                .WhereOneOrMany(currentFolders, e => e.ParentId)
+                .Select(e => e.ChildId)
+                .ToArray();
+
+            var allChildren = directChildren.Concat(linkedChildren).Distinct().ToArray();
+
+            if (allChildren.Length == 0)
+            {
+                break;
+            }
+
+            var childFolders = context.BaseItems
+                .WhereOneOrMany(allChildren, e => e.Id)
+                .Where(e => e.IsFolder)
+                .Select(e => e.Id)
+                .ToHashSet();
+
+            foreach (var childId in allChildren)
+            {
+                if (visited.Add(childId) && childFolders.Contains(childId))
+                {
+                    folderStack.Add(childId);
+                }
+            }
+        }
+
+        return visited;
+    }
+
+    /// <summary>
+    /// Traverses UP the hierarchy from items to find all ancestor folders.
+    /// </summary>
+    private static HashSet<Guid> TraverseHierarchyUp(JellyfinDbContext context, ICollection<Guid> startIds)
+    {
+        var ancestors = new HashSet<Guid>();
+        var itemStack = new HashSet<Guid>(startIds);
+
+        while (itemStack.Count != 0)
+        {
+            var currentItems = itemStack.ToArray();
+            itemStack.Clear();
+
+            var ancestorParents = context.AncestorIds
+                .WhereOneOrMany(currentItems, e => e.ItemId)
+                .Select(e => e.ParentItemId)
+                .ToArray();
+
+            var linkedParents = context.LinkedChildren
+                .WhereOneOrMany(currentItems, e => e.ChildId)
+                .Select(e => e.ParentId)
+                .ToArray();
+
+            foreach (var parentId in ancestorParents.Concat(linkedParents))
+            {
+                if (ancestors.Add(parentId))
+                {
+                    itemStack.Add(parentId);
+                }
+            }
+        }
+
+        return ancestors;
+    }
+}

src/Jellyfin.Database/Jellyfin.Database.Implementations/IDescendantQueryProvider.cs

@@ -1,30 +0,0 @@
-using System;
-using System.Linq;
-using Jellyfin.Database.Implementations.MatchCriteria;
-
-namespace Jellyfin.Database.Implementations;
-
-/// <summary>
-/// Provider interface for descendant queries using recursive CTEs.
-/// Each database provider implements this with provider-specific SQL.
-/// </summary>
-public interface IDescendantQueryProvider
-{
-    /// <summary>
-    /// Gets a queryable of all descendant IDs for a parent item.
-    /// Uses recursive CTE to traverse AncestorIds and LinkedChildren infinitely.
-    /// </summary>
-    /// <param name="context">Database context.</param>
-    /// <param name="parentId">Parent item ID.</param>
-    /// <returns>Queryable of descendant item IDs.</returns>
-    IQueryable<Guid> GetAllDescendantIds(JellyfinDbContext context, Guid parentId);
-
-    /// <summary>
-    /// Gets a queryable of all folder IDs that have any descendant matching the specified criteria.
-    /// Uses recursive CTE for infinite depth traversal. Can be used in LINQ .Contains() expressions.
-    /// </summary>
-    /// <param name="context">Database context.</param>
-    /// <param name="criteria">The matching criteria to apply.</param>
-    /// <returns>Queryable of folder IDs.</returns>
-    IQueryable<Guid> GetFolderIdsMatching(JellyfinDbContext context, FolderMatchCriteria criteria);
-}

src/Jellyfin.Database/Jellyfin.Database.Implementations/IJellyfinDatabaseProvider.cs

@@ -17,12 +17,6 @@ public interface IJellyfinDatabaseProvider
     /// </summary>
     IDbContextFactory<JellyfinDbContext>? DbContextFactory { get; set; }
 
-    /// <summary>
-    /// Gets the descendant query provider for this database type.
-    /// Used for recursive CTE queries to find all descendants of an item.
-    /// </summary>
-    IDescendantQueryProvider DescendantQueryProvider { get; }
-
     /// <summary>
     /// Initialises jellyfins EFCore database access.
     /// </summary>