1 files changed, 65 insertions, 5 deletions

diff --git a/tests/Jellyfin.Server.Implementations.Tests/Dto/DtoServiceImageInheritanceTests.cs b/tests/Jellyfin.Server.Implementations.Tests/Dto/DtoServiceImageInheritanceTests.cs
index 96625ae670..6b6240e116 100644
--- a/tests/Jellyfin.Server.Implementations.Tests/Dto/DtoServiceImageInheritanceTests.cs
+++ b/tests/Jellyfin.Server.Implementations.Tests/Dto/DtoServiceImageInheritanceTests.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Emby.Server.Implementations.Dto;
 using Emby.Server.Implementations.Playlists;
 using Jellyfin.Data.Enums;
@@ -7,9 +8,9 @@ using MediaBrowser.Controller.Chapters;
 using MediaBrowser.Controller.Drawing;
 using MediaBrowser.Controller.Dto;
 using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Entities.Audio;
 using MediaBrowser.Controller.Library;
 using MediaBrowser.Controller.LiveTv;
-using MediaBrowser.Controller.MediaEncoding;
 using MediaBrowser.Controller.Providers;
 using MediaBrowser.Controller.Trickplay;
 using MediaBrowser.Model.Entities;
@@ -99,9 +100,72 @@ public class DtoServiceImageInheritanceTests
         Assert.Equal("/images/generated.png", dto.ImageTags[ImageType.Primary]);
     }
 
+    [Fact]
+    public void GetBaseItemDtos_MusicAlbums_ResolveInheritedThumbFromArtistBatch_WithoutPerAlbumLookup()
+    {
+        var artist = new MusicArtist
+        {
+            Id = Guid.NewGuid(),
+            Name = "Some Artist",
+            ImageInfos =
+            [
+                new ItemImageInfo
+                {
+                    Type = ImageType.Thumb,
+                    Path = "/images/artist-thumb.jpg",
+                    DateModified = new DateTime(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc)
+                }
+            ]
+        };
+
+        static MusicAlbum MakeAlbum() => new MusicAlbum
+        {
+            Id = Guid.NewGuid(),
+            Name = "Album",
+            AlbumArtists = ["Some Artist"],
+            ImageInfos = []
+        };
+
+        var libraryManager = new Mock<ILibraryManager>();
+
+        // DtoService resolves every album-artist name in ONE batch (GetArtists). The album's inherited
+        // Thumb/Backdrop images must come from that batch, not a per-album GetArtist/GetItemList lookup
+        // (the N+1). GetArtist is intentionally left unset: a regression to the per-album path would
+        // resolve no artist and fail the assertions below.
+        libraryManager
+            .Setup(x => x.GetArtists(It.IsAny<IReadOnlyList<string>>()))
+            .Returns(new Dictionary<string, MusicArtist[]>(StringComparer.OrdinalIgnoreCase)
+            {
+                ["Some Artist"] = [artist]
+            });
+
+        var dtoService = BuildDtoService(libraryManager);
+
+        var dtos = dtoService.GetBaseItemDtos([MakeAlbum(), MakeAlbum()], new DtoOptions(false));
+
+        Assert.Equal(2, dtos.Count);
+        foreach (var dto in dtos)
+        {
+            Assert.Equal(artist.Id, dto.ParentThumbItemId);
+            Assert.Equal("/images/artist-thumb.jpg", dto.ParentThumbImageTag);
+        }
+
+        // The artist lookup is batched once for the whole set, never once per album.
+        libraryManager.Verify(x => x.GetArtists(It.IsAny<IReadOnlyList<string>>()), Times.Once);
+        libraryManager.Verify(x => x.GetArtist(It.IsAny<string>(), It.IsAny<DtoOptions>()), Times.Never);
+    }
+
     private static DtoService BuildDtoService(BaseItem displayParent)
     {
         var libraryManager = new Mock<ILibraryManager>();
+        libraryManager
+            .Setup(x => x.GetItemById(displayParent.Id))
+            .Returns(displayParent);
+        return BuildDtoService(libraryManager);
+    }
+
+    private static DtoService BuildDtoService(Mock<ILibraryManager> libraryManager)
+    {
         var userDataManager = new Mock<IUserDataManager>();
         var imageProcessor = new Mock<IImageProcessor>();
         var providerManager = new Mock<IProviderManager>();
@@ -113,10 +177,6 @@ public class DtoServiceImageInheritanceTests
         var chapterManager = new Mock<IChapterManager>();
         var logger = new Mock<Microsoft.Extensions.Logging.ILogger<DtoService>>();
 
-        libraryManager
-            .Setup(x => x.GetItemById(displayParent.Id))
-            .Returns(displayParent);
-
         imageProcessor
             .Setup(x => x.GetImageCacheTag(It.IsAny<BaseItem>(), It.IsAny<ItemImageInfo>()))
             .Returns<BaseItem, ItemImageInfo>((_, image) => image.Path);