fix(mobile): avoid duplicate assets in album view (#28152)

fix(mobile): avoid duplicate assets in remote album timeline

Co-authored-by: Stefan Friedli <stefan@stefanfriedli.ch>

mobile/lib/infrastructure/repositories/timeline.repository.dart

@@ -244,17 +244,21 @@ class DriftTimelineRepository extends DriftDatabaseRepository {
 
     final isAscending = albumData.order == AlbumAssetOrder.asc;
 
-    final query = _db.remoteAssetEntity.select().addColumns([_db.localAssetEntity.id]).join([
+    // Correlated subquery picks the first matching local asset by checksum,
+    // avoiding fan-out when the same photo exists in multiple device albums (#23273).
+    final localId = subqueryExpression<String>(
+      _db.localAssetEntity.selectOnly()
+        ..addColumns([_db.localAssetEntity.id])
+        ..where(_db.localAssetEntity.checksum.equalsExp(_db.remoteAssetEntity.checksum))
+        ..limit(1),
+    );
+
+    final query = _db.remoteAssetEntity.select().addColumns([localId]).join([
       innerJoin(
         _db.remoteAlbumAssetEntity,
         _db.remoteAlbumAssetEntity.assetId.equalsExp(_db.remoteAssetEntity.id),
         useColumns: false,
       ),
-      leftOuterJoin(
-        _db.localAssetEntity,
-        _db.remoteAssetEntity.checksum.equalsExp(_db.localAssetEntity.checksum),
-        useColumns: false,
-      ),
     ])..where(_db.remoteAssetEntity.deletedAt.isNull() & _db.remoteAlbumAssetEntity.albumId.equals(albumId));
 
     if (isAscending) {
@@ -265,9 +269,7 @@ class DriftTimelineRepository extends DriftDatabaseRepository {
 
     query.limit(count, offset: offset);
 
-    return query
+    return query.map((row) => row.readTable(_db.remoteAssetEntity).toDto(localId: row.read(localId))).get();
-        .map((row) => row.readTable(_db.remoteAssetEntity).toDto(localId: row.read(_db.localAssetEntity.id)))
-        .get();
   }
 
   TimelineQuery fromAssets(List<BaseAsset> assets, TimelineOrigin origin) => (

mobile/test/medium/repositories/timeline_repository_test.dart

@@ -0,0 +1,41 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:immich_mobile/domain/models/asset/base_asset.model.dart';
+import 'package:immich_mobile/domain/models/timeline.model.dart';
+import 'package:immich_mobile/infrastructure/repositories/timeline.repository.dart';
+
+import '../repository_context.dart';
+
+void main() {
+  late MediumRepositoryContext ctx;
+  late DriftTimelineRepository sut;
+
+  setUp(() {
+    ctx = MediumRepositoryContext();
+    sut = DriftTimelineRepository(ctx.db);
+  });
+
+  tearDown(() async {
+    await ctx.dispose();
+  });
+
+  group('remoteAlbum assets', () {
+    test('no duplicate assets when identical checksum appears in multiple local asset rows', () async {
+      // Regression check for #23273: a LEFT OUTER JOIN on checksum would fan out and create duplicates
+      // happens when same photo exists in multiple albums on device
+      final user = await ctx.newUser();
+      final checksum = 'yolo';
+      final album = await ctx.newRemoteAlbum(ownerId: user.id);
+      final remoteAsset = await ctx.newRemoteAsset(ownerId: user.id, checksum: checksum);
+      await ctx.insertRemoteAlbumAsset(albumId: album.id, assetId: remoteAsset.id);
+
+      final localAsset1 = await ctx.newLocalAsset(checksum: checksum);
+      final localAsset2 = await ctx.newLocalAsset(checksum: checksum);
+
+      final assets = await sut.remoteAlbum(album.id, GroupAssetsBy.day).assetSource(0, 10);
+
+      expect(assets, hasLength(1));
+      expect((assets.first as RemoteAsset).id, remoteAsset.id);
+      expect([localAsset1.id, localAsset2.id], contains((assets.first as RemoteAsset).localId));
+    });
+  });
+}