Fix artist duplicates

Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs

@@ -390,7 +390,8 @@ public sealed partial class BaseItemRepository
         {
             if (filter.UseRawName == true)
             {
-                baseQuery = baseQuery.Where(e => e.Name == filter.Name);
+                var nameLower = filter.Name.ToLowerInvariant();
+                baseQuery = baseQuery.Where(e => e.Name!.ToLower() == nameLower);
             }
             else
             {

Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs

@@ -1,4 +1,6 @@
 #pragma warning disable RS0030 // Do not use banned APIs
+#pragma warning disable CA1304 // Specify CultureInfo
+#pragma warning disable CA1311 // Specify a culture or use an invariant version
 
 using System;
 using System.Collections.Generic;
@@ -62,17 +64,19 @@ public class LinkedChildrenService : ILinkedChildrenService
     {
         using var dbContext = _dbProvider.CreateDbContext();
 
+        var lowerNames = artistNames.Select(n => n.ToLowerInvariant()).ToArray();
         var artists = dbContext.BaseItems
             .AsNoTracking()
             .Where(e => e.Type == _itemTypeLookup.BaseItemKindNames[BaseItemKind.MusicArtist]!)
-            .Where(e => artistNames.Contains(e.Name))
+            .Where(e => lowerNames.Contains(e.Name!.ToLower()))
             .ToArray();
 
         var lookup = artists
-            .GroupBy(e => e.Name!)
+            .GroupBy(e => e.Name!, StringComparer.OrdinalIgnoreCase)
             .ToDictionary(
                 g => g.Key,
-                g => g.Select(f => _queryHelpers.DeserializeBaseItem(f)).Where(dto => dto is not null).Cast<MusicArtist>().ToArray());
+                g => g.Select(f => _queryHelpers.DeserializeBaseItem(f)).Where(dto => dto is not null).Cast<MusicArtist>().ToArray(),
+                StringComparer.OrdinalIgnoreCase);
 
         var result = new Dictionary<string, MusicArtist[]>(artistNames.Count);
         foreach (var name in artistNames)

Jellyfin.Server/Migrations/Routines/MergeDuplicateMusicArtists.cs

@@ -0,0 +1,204 @@
+#pragma warning disable RS0030 // Do not use banned APIs
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Jellyfin.Database.Implementations;
+using Jellyfin.Server.ServerSetupApp;
+using MediaBrowser.Controller.Library;
+using MediaBrowser.Controller.Persistence;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+
+namespace Jellyfin.Server.Migrations.Routines;
+
+/// <summary>
+/// Merges MusicArtist records that differ only by Name casing. Prior to the case-insensitive
+/// dedup lookup added alongside this migration, the artist validator would create a second
+/// MusicArtist whenever a track tagged the artist with a different casing than the
+/// resolver-created one (e.g. "Thirty Seconds To Mars" vs. "Thirty Seconds to Mars").
+/// </summary>
+[JellyfinMigration("2026-05-08T12:00:00", nameof(MergeDuplicateMusicArtists))]
+[JellyfinMigrationBackup(JellyfinDb = true)]
+public class MergeDuplicateMusicArtists : IAsyncMigrationRoutine
+{
+    private const string MusicArtistType = "MediaBrowser.Controller.Entities.Audio.MusicArtist";
+
+    private readonly IStartupLogger<MergeDuplicateMusicArtists> _logger;
+    private readonly IDbContextFactory<JellyfinDbContext> _dbContextFactory;
+    private readonly ILibraryManager _libraryManager;
+    private readonly IItemPersistenceService _persistenceService;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MergeDuplicateMusicArtists"/> class.
+    /// </summary>
+    /// <param name="logger">The startup logger.</param>
+    /// <param name="dbContextFactory">The database context factory.</param>
+    /// <param name="libraryManager">The library manager.</param>
+    /// <param name="persistenceService">The item persistence service.</param>
+    public MergeDuplicateMusicArtists(
+        IStartupLogger<MergeDuplicateMusicArtists> logger,
+        IDbContextFactory<JellyfinDbContext> dbContextFactory,
+        ILibraryManager libraryManager,
+        IItemPersistenceService persistenceService)
+    {
+        _logger = logger;
+        _dbContextFactory = dbContextFactory;
+        _libraryManager = libraryManager;
+        _persistenceService = persistenceService;
+    }
+
+    /// <inheritdoc/>
+    public async Task PerformAsync(CancellationToken cancellationToken)
+    {
+        var context = await _dbContextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
+        await using (context.ConfigureAwait(false))
+        {
+            var artists = await context.BaseItems
+                .Where(b => b.Type == MusicArtistType && b.Name != null)
+                .Select(b => new { b.Id, b.Name, b.DateCreated })
+                .ToListAsync(cancellationToken)
+                .ConfigureAwait(false);
+
+            var groups = artists
+                .GroupBy(a => a.Name!.ToLowerInvariant())
+                .Where(g => g.Count() > 1)
+                .ToList();
+
+            if (groups.Count == 0)
+            {
+                _logger.LogInformation("No case-only duplicate MusicArtist records found.");
+                return;
+            }
+
+            _logger.LogInformation("Found {Count} groups of case-only duplicate MusicArtist records.", groups.Count);
+
+            var idsToDelete = new List<Guid>();
+            foreach (var group in groups)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+
+                var groupIds = group.Select(g => g.Id).ToArray();
+
+                // Pick the keeper: the artist with the most child references is the "real" one
+                // (the resolver-created artist with a filesystem path); the duplicates are usually
+                // empty stubs created by the validator's case-sensitive miss.
+                var stats = await context.BaseItems
+                    .Where(b => groupIds.Contains(b.Id))
+                    .Select(b => new
+                    {
+                        b.Id,
+                        b.Name,
+                        b.DateCreated,
+                        ChildCount = context.BaseItems.Count(c => c.ParentId == b.Id),
+                        AncestorCount = context.AncestorIds.Count(a => a.ParentItemId == b.Id),
+                        LinkedCount = context.LinkedChildren.Count(l => l.ParentId == b.Id || l.ChildId == b.Id),
+                    })
+                    .ToListAsync(cancellationToken)
+                    .ConfigureAwait(false);
+
+                var keeper = stats
+                    .OrderByDescending(s => s.ChildCount)
+                    .ThenByDescending(s => s.AncestorCount)
+                    .ThenByDescending(s => s.LinkedCount)
+                    .ThenBy(s => s.DateCreated)
+                    .First();
+
+                foreach (var dup in stats.Where(s => s.Id != keeper.Id))
+                {
+                    var keeperId = keeper.Id;
+                    var dupId = dup.Id;
+
+                    await context.BaseItems
+                        .Where(b => b.ParentId == dupId)
+                        .ExecuteUpdateAsync(s => s.SetProperty(b => b.ParentId, keeperId), cancellationToken)
+                        .ConfigureAwait(false);
+
+                    await context.BaseItems
+                        .Where(b => b.OwnerId == dupId)
+                        .ExecuteUpdateAsync(s => s.SetProperty(b => b.OwnerId, keeperId), cancellationToken)
+                        .ConfigureAwait(false);
+
+                    // AncestorIds PK is (ItemId, ParentItemId); drop rows that would collide before redirecting.
+                    await context.AncestorIds
+                        .Where(a => a.ParentItemId == dupId
+                            && context.AncestorIds.Any(k => k.ParentItemId == keeperId && k.ItemId == a.ItemId))
+                        .ExecuteDeleteAsync(cancellationToken)
+                        .ConfigureAwait(false);
+                    await context.AncestorIds
+                        .Where(a => a.ParentItemId == dupId)
+                        .ExecuteUpdateAsync(s => s.SetProperty(a => a.ParentItemId, keeperId), cancellationToken)
+                        .ConfigureAwait(false);
+
+                    // LinkedChildren PK is (ParentId, ChildId); drop colliding rows in both directions.
+                    await context.LinkedChildren
+                        .Where(l => l.ParentId == dupId
+                            && context.LinkedChildren.Any(k => k.ParentId == keeperId && k.ChildId == l.ChildId))
+                        .ExecuteDeleteAsync(cancellationToken)
+                        .ConfigureAwait(false);
+                    await context.LinkedChildren
+                        .Where(l => l.ParentId == dupId)
+                        .ExecuteUpdateAsync(s => s.SetProperty(l => l.ParentId, keeperId), cancellationToken)
+                        .ConfigureAwait(false);
+                    await context.LinkedChildren
+                        .Where(l => l.ChildId == dupId
+                            && context.LinkedChildren.Any(k => k.ChildId == keeperId && k.ParentId == l.ParentId))
+                        .ExecuteDeleteAsync(cancellationToken)
+                        .ConfigureAwait(false);
+                    await context.LinkedChildren
+                        .Where(l => l.ChildId == dupId)
+                        .ExecuteUpdateAsync(s => s.SetProperty(l => l.ChildId, keeperId), cancellationToken)
+                        .ConfigureAwait(false);
+
+                    // UserData has UNIQUE(UserId, CustomDataKey); keep the dup's row only when the
+                    // keeper has no equivalent row, otherwise the keeper's value wins.
+                    await context.UserData
+                        .Where(u => u.ItemId == dupId
+                            && context.UserData.Any(k => k.ItemId == keeperId && k.UserId == u.UserId && k.CustomDataKey == u.CustomDataKey))
+                        .ExecuteDeleteAsync(cancellationToken)
+                        .ConfigureAwait(false);
+                    await context.UserData
+                        .Where(u => u.ItemId == dupId)
+                        .ExecuteUpdateAsync(s => s.SetProperty(u => u.ItemId, keeperId), cancellationToken)
+                        .ConfigureAwait(false);
+
+                    idsToDelete.Add(dupId);
+                }
+
+                _logger.LogDebug(
+                    "Merged duplicates for '{Name}' into {KeeperId} ({Removed} removed).",
+                    keeper.Name,
+                    keeper.Id,
+                    stats.Count - 1);
+            }
+
+            if (idsToDelete.Count == 0)
+            {
+                return;
+            }
+
+            // Resolve via LibraryManager so DeleteItemsUnsafeFast can also remove the
+            // %MetadataPath%/artists/<Name> directories that the duplicate stubs left behind.
+            // Fall back to the persistence service for any items the LibraryManager can't resolve.
+            var itemsToDelete = idsToDelete
+                .Select(id => _libraryManager.GetItemById(id))
+                .Where(item => item is not null)
+                .ToList();
+            if (itemsToDelete.Count > 0)
+            {
+                _libraryManager.DeleteItemsUnsafeFast(itemsToDelete!);
+            }
+
+            var deletedIds = itemsToDelete.Select(i => i!.Id).ToHashSet();
+            var unresolvedIds = idsToDelete.Where(id => !deletedIds.Contains(id)).ToList();
+            if (unresolvedIds.Count > 0)
+            {
+                _persistenceService.DeleteItem(unresolvedIds);
+            }
+
+            _logger.LogInformation("Removed {Count} duplicate MusicArtist records.", idsToDelete.Count);
+        }
+    }
+}