From 8e80677bdd6471d04748cfcca41f997f2f48b341 Mon Sep 17 00:00:00 2001
From: Shadowghost <Ghost_of_Stone@web.de>
Date: Fri, 21 Aug 2026 22:48:47 +0200
Subject: Fix series merging leaking across libraries and under-counting merged
 children

---
 .../DescendantQueryHelper.cs                       | 25 ++++++++++++++++++++++
 1 file changed, 25 insertions(+)

(limited to 'src/Jellyfin.Database/Jellyfin.Database.Implementations')

diff --git a/src/Jellyfin.Database/Jellyfin.Database.Implementations/DescendantQueryHelper.cs b/src/Jellyfin.Database/Jellyfin.Database.Implementations/DescendantQueryHelper.cs
index bfd0fac34a..909609e35d 100644
--- a/src/Jellyfin.Database/Jellyfin.Database.Implementations/DescendantQueryHelper.cs
+++ b/src/Jellyfin.Database/Jellyfin.Database.Implementations/DescendantQueryHelper.cs
@@ -39,6 +39,31 @@ public static class DescendantQueryHelper
         return descendants.AsQueryable();
     }
 
+    /// <summary>
+    /// Gets all descendant IDs for multiple parent items in a single traversal.
+    /// Traverses AncestorIds and LinkedChildren, like <see cref="GetAllDescendantIds"/>.
+    /// </summary>
+    /// <param name="context">Database context.</param>
+    /// <param name="parentIds">Parent item IDs.</param>
+    /// <returns>Set of all descendant item IDs (excluding the parent IDs themselves).</returns>
+    public static HashSet<Guid> GetAllDescendantIdsBatch(JellyfinDbContext context, IReadOnlyList<Guid> parentIds)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+        ArgumentNullException.ThrowIfNull(parentIds);
+
+        if (parentIds.Count == 0)
+        {
+            return [];
+        }
+
+        var seedSet = new HashSet<Guid>(parentIds);
+        var descendants = TraverseHierarchyDown(context, seedSet);
+
+        descendants.ExceptWith(seedSet);
+
+        return descendants;
+    }
+
     /// <summary>
     /// Gets a queryable of all owned descendant IDs for a parent item.
     /// Traverses only AncestorIds (hierarchical ownership), NOT LinkedChildren (associations).
-- 
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