show album disc titles instead of generic disc numbers

Navidrome and gonic expose OpenSubsonic discTitles on the album response.
Parse them into a transient Album.discTitles map and persist each album's
titles in a child discs table (sourceId, albumId, disc, title) cascading
from albums. Songs keep only their disc number, and the album screen joins
by disc to render a title when one exists, falling back to "Disc N".

Titles are read opportunistically: a server that doesn't send discTitles
just leaves the table empty, so no API version negotiation is needed.
Titles apply to single- and multi-disc albums, are pruned when removed,
and are stored per album.

Schema 10 -> 11.

app/src/main/kotlin/com/subtracks/data/db/LibraryDao.kt

@@ -8,6 +8,8 @@ import androidx.room3.Upsert
 import androidx.room3.paging.PagingSourceDaoReturnTypeConverter
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.Artist
+import com.subtracks.data.model.Disc
+import com.subtracks.data.model.DiscKey
 import com.subtracks.data.model.Playlist
 import com.subtracks.data.model.PlaylistSong
 import com.subtracks.data.model.Song
@@ -66,6 +68,9 @@ interface LibraryDao {
     @Query("SELECT id FROM albums WHERE sourceId = :sourceId")
     suspend fun albumIds(sourceId: Long): List<String>
 
+    @Query("SELECT albumId, disc FROM discs WHERE sourceId = :sourceId")
+    suspend fun discKeys(sourceId: Long): List<DiscKey>
+
     @Query("SELECT id FROM playlists WHERE sourceId = :sourceId")
     suspend fun playlistIds(sourceId: Long): List<String>
 
@@ -84,6 +89,13 @@ interface LibraryDao {
         ids: Collection<String>,
     )
 
+    @Query("DELETE FROM discs WHERE sourceId = :sourceId AND albumId = :albumId AND disc = :disc")
+    suspend fun deleteDisc(
+        sourceId: Long,
+        albumId: String,
+        disc: Long,
+    )
+
     @Query("DELETE FROM playlists WHERE sourceId = :sourceId AND id IN (:ids)")
     suspend fun deletePlaylists(
         sourceId: Long,
@@ -541,6 +553,12 @@ interface LibraryDao {
         artistId: String,
     ): Flow<List<Album>>
 
+    @Query("SELECT * FROM discs WHERE sourceId = :sourceId AND albumId = :albumId ORDER BY disc")
+    fun discs(
+        sourceId: Long,
+        albumId: String,
+    ): Flow<List<Disc>>
+
     @Query("SELECT * FROM playlists WHERE sourceId = :sourceId AND id = :playlistId")
     fun playlist(
         sourceId: Long,

app/src/main/kotlin/com/subtracks/data/db/Migrations.kt

@@ -93,6 +93,18 @@ val MIGRATION_9_10 =
         }
     }
 
+val MIGRATION_10_11 =
+    object : Migration(10, 11) {
+        override suspend fun migrate(connection: SQLiteConnection) {
+            connection.execSQL(
+                "CREATE TABLE IF NOT EXISTS `discs` (`sourceId` INTEGER NOT NULL, `albumId` TEXT NOT NULL, " +
+                    "`disc` INTEGER NOT NULL, `title` TEXT NOT NULL, PRIMARY KEY(`sourceId`, `albumId`, `disc`), " +
+                    "FOREIGN KEY(`sourceId`, `albumId`) REFERENCES `albums`(`sourceId`, `id`) ON UPDATE NO ACTION ON DELETE CASCADE )",
+            )
+            connection.execSQL("CREATE INDEX IF NOT EXISTS `index_discs_sourceId_albumId` ON `discs` (`sourceId`, `albumId`)")
+        }
+    }
+
 val MIGRATIONS: Array<Migration> =
     arrayOf(
         MIGRATION_1_2,
@@ -104,4 +116,5 @@ val MIGRATIONS: Array<Migration> =
         MIGRATION_7_8,
         MIGRATION_8_9,
         MIGRATION_9_10,
+        MIGRATION_10_11,
     )

app/src/main/kotlin/com/subtracks/data/db/SubtracksDatabase.kt

@@ -6,6 +6,7 @@ import androidx.room3.RoomDatabase
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.Artist
 import com.subtracks.data.model.ArtworkSeed
+import com.subtracks.data.model.Disc
 import com.subtracks.data.model.PlaybackCursor
 import com.subtracks.data.model.Playlist
 import com.subtracks.data.model.PlaylistSong
@@ -22,6 +23,7 @@ import com.subtracks.data.model.SubsonicSource
         SubsonicSource::class,
         Artist::class,
         Album::class,
+        Disc::class,
         Playlist::class,
         PlaylistSong::class,
         Song::class,
@@ -30,7 +32,7 @@ import com.subtracks.data.model.SubsonicSource
         ShuffleOrder::class,
         ArtworkSeed::class,
     ],
-    version = 10,
+    version = 11,
     exportSchema = true,
 )
 @ColumnTypeConverters(QueueKindConverter::class)

app/src/main/kotlin/com/subtracks/data/model/Models.kt

@@ -5,6 +5,7 @@ import androidx.room3.ColumnTypeConverter
 import androidx.room3.Embedded
 import androidx.room3.Entity
 import androidx.room3.ForeignKey
+import androidx.room3.Ignore
 import androidx.room3.Index
 import androidx.room3.PrimaryKey
 
@@ -85,6 +86,27 @@ data class Album(
     val songCount: Long,
     val frequentRank: Long?,
     val recentRank: Long?,
+    @Ignore val discTitles: Map<Long, String> = emptyMap(),
+)
+
+@Entity(
+    tableName = "discs",
+    primaryKeys = ["sourceId", "albumId", "disc"],
+    foreignKeys = [
+        ForeignKey(
+            entity = Album::class,
+            parentColumns = ["sourceId", "id"],
+            childColumns = ["sourceId", "albumId"],
+            onDelete = ForeignKey.CASCADE,
+        ),
+    ],
+    indices = [Index("sourceId", "albumId")],
+)
+data class Disc(
+    val sourceId: Long,
+    val albumId: String,
+    val disc: Long,
+    val title: String,
 )
 
 @Entity(
@@ -166,6 +188,11 @@ data class SongListItem(
     val coverArt: String?,
 )
 
+data class DiscKey(
+    val albumId: String,
+    val disc: Long,
+)
+
 enum class QueueKind { Playlist, Album, Song, Songs }
 
 @Entity(

app/src/main/kotlin/com/subtracks/data/repo/LibraryRepository.kt

@@ -7,6 +7,7 @@ import androidx.paging.PagingSource
 import com.subtracks.data.db.SubtracksDatabase
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.Artist
+import com.subtracks.data.model.Disc
 import com.subtracks.data.model.Playlist
 import com.subtracks.data.model.Song
 import com.subtracks.data.model.SongListItem
@@ -213,6 +214,11 @@ class LibraryRepository(
         artistId: String,
     ): Flow<List<Album>> = db.libraryDao().albumsForArtist(sourceId, artistId)
 
+    fun albumDiscs(
+        sourceId: Long,
+        albumId: String,
+    ): Flow<List<Disc>> = db.libraryDao().discs(sourceId, albumId)
+
     fun albumSongs(
         sourceId: Long,
         albumId: String,

app/src/main/kotlin/com/subtracks/data/source/subsonic/SubsonicXml.kt

@@ -53,6 +53,7 @@ object SubsonicXml {
             songCount = element.longAttr("songCount") ?: 0L,
             frequentRank = null,
             recentRank = null,
+            discTitles = element.discTitles(),
         )
 
     fun songs(
@@ -116,6 +117,20 @@ object SubsonicXml {
         }
 }
 
+private fun Element.discTitles(): Map<Long, String> =
+    childElements("discTitles")
+        .mapNotNull { title ->
+            val disc = title.longAttr("disc") ?: return@mapNotNull null
+            title.attr("title").takeIf { it.isNotBlank() }?.let { disc to it }
+        }.toMap()
+
+private fun Element.childElements(tag: String): List<Element> {
+    val children = childNodes
+    return (0 until children.length).mapNotNull { index ->
+        (children.item(index) as? Element)?.takeIf { it.tagName == tag }
+    }
+}
+
 private fun Element.elements(tag: String): List<Element> {
     val nodes = getElementsByTagName(tag)
     return (0 until nodes.length).mapNotNull { nodes.item(it) as? Element }

app/src/main/kotlin/com/subtracks/data/sync/SyncService.kt

@@ -7,6 +7,8 @@ import androidx.sqlite.SQLiteStatement
 import com.subtracks.data.db.SubtracksDatabase
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.Artist
+import com.subtracks.data.model.Disc
+import com.subtracks.data.model.DiscKey
 import com.subtracks.data.model.Playlist
 import com.subtracks.data.model.PlaylistSong
 import com.subtracks.data.model.Song
@@ -25,6 +27,10 @@ class SyncService(
             val artists = source.getArtists()
             val albums = source.getAlbums()
             val songs = source.getSongs()
+            val discs =
+                albums.flatMap { album ->
+                    album.discTitles.map { (disc, title) -> Disc(album.sourceId, album.id, disc, title) }
+                }
             val playlists = source.getPlaylists()
             val playlistSongs = source.getPlaylistSongs(playlists)
 
@@ -32,6 +38,7 @@ class SyncService(
                 transactor.immediateTransaction {
                     upsertChanged("artists", artistColumns, primaryKey, artists) { it.values() }
                     upsertChanged("albums", albumColumns, primaryKey, albums) { it.values() }
+                    upsertChanged("discs", discColumns, discKey, discs) { it.values() }
                     upsertChanged("songs", songColumns, primaryKey, songs) { it.values() }
                     upsertChanged("playlists", playlistColumns, primaryKey, playlists) { it.values() }
                     upsertChanged("playlist_songs", playlistSongColumns, playlistSongKey, playlistSongs) { it.values() }
@@ -41,12 +48,16 @@ class SyncService(
                     val existingAlbumIds = library.albumIds(source.id)
                     val existingSongIds = library.songIds(source.id)
                     val existingPlaylistIds = library.playlistIds(source.id)
+                    val existingDiscKeys = library.discKeys(source.id)
 
                     prune(existingArtistIds, artists.map { it.id }) { library.deleteArtists(source.id, it) }
                     prune(existingAlbumIds, albums.map { it.id }) { library.deleteAlbums(source.id, it) }
                     prune(existingSongIds, songs.map { it.id }) { library.deleteSongs(source.id, it) }
                     prune(existingPlaylistIds, playlists.map { it.id }) { library.deletePlaylists(source.id, it) }
 
+                    val currentDiscKeys = discs.mapTo(HashSet()) { DiscKey(it.albumId, it.disc) }
+                    existingDiscKeys.filterNot { it in currentDiscKeys }.forEach { library.deleteDisc(source.id, it.albumId, it.disc) }
+
                     val playlistSongCounts = playlistSongs.groupingBy { it.playlistId }.eachCount()
                     playlists.forEach { playlist ->
                         library.deletePlaylistSongsFrom(source.id, playlist.id, (playlistSongCounts[playlist.id] ?: 0).toLong())
@@ -90,6 +101,10 @@ private val albumColumns =
         "recentRank",
     )
 
+private val discKey = listOf("sourceId", "albumId", "disc")
+
+private val discColumns = listOf("sourceId", "albumId", "disc", "title")
+
 private val songColumns =
     listOf(
         "sourceId",
@@ -118,6 +133,8 @@ private fun Artist.values() = listOf<Any?>(sourceId, id, name, albumCount, starr
 private fun Album.values() =
     listOf<Any?>(sourceId, id, artistId, name, albumArtist, created, coverArt, genre, year, starred, songCount, frequentRank, recentRank)
 
+private fun Disc.values() = listOf<Any?>(sourceId, albumId, disc, title)
+
 private fun Song.values() =
     listOf<Any?>(sourceId, id, albumId, artistId, title, album, artist, duration, track, disc, starred, genre, created)
 

app/src/main/kotlin/com/subtracks/ui/library/AlbumDetailScreen.kt

@@ -12,6 +12,7 @@ import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.CoverArtRef
+import com.subtracks.data.model.Disc
 import com.subtracks.data.model.QueueKind
 import com.subtracks.data.model.Song
 import com.subtracks.playback.PlaybackController
@@ -36,12 +37,14 @@ fun AlbumDetailRoute(
 ) {
     val album by viewModel.album.collectAsStateWithLifecycle(initialValue = null)
     val songs by viewModel.songs.collectAsStateWithLifecycle(initialValue = emptyList())
+    val discs by viewModel.discs.collectAsStateWithLifecycle(initialValue = emptyList())
     val playback by playbackController.state.collectAsStateWithLifecycle()
     val context = playback.context
     val shortcutArt = remember(coverArtId) { coverArtId?.let { viewModel.coverArt(it, true) } }
     AlbumDetailScreen(
         album = album,
         songs = songs,
+        discs = discs,
         coverArt = viewModel::coverArt,
         artwork = rememberArtworkColors(shortcutArt ?: viewModel.coverArt(album?.coverArt, true), THEME_TRANSITION_MS),
         onBack = onBack,
@@ -56,6 +59,7 @@ fun AlbumDetailRoute(
 fun AlbumDetailScreen(
     album: Album?,
     songs: List<Song>,
+    discs: List<Disc> = emptyList(),
     coverArt: (String?, Boolean) -> CoverArtRef?,
     artwork: ArtworkColors?,
     onBack: () -> Unit,
@@ -68,6 +72,7 @@ fun AlbumDetailScreen(
     modifier: Modifier = Modifier,
 ) {
     val multiDisc = songs.map { it.disc ?: 1L }.distinct().size > 1
+    val discTitles = remember(discs) { discs.associate { it.disc to it.title } }
     HeroDetailScaffold(
         artwork = artwork,
         title = album?.name.orEmpty(),
@@ -95,8 +100,9 @@ fun AlbumDetailScreen(
             var lastDisc: Long? = null
             songs.forEachIndexed { index, song ->
                 val disc = song.disc ?: 1L
-                if (multiDisc && disc != lastDisc) {
-                    item(key = "disc:$disc") { DiscHeader(disc) }
+                val discTitle = discTitles[disc]
+                if (disc != lastDisc && (multiDisc || !discTitle.isNullOrBlank())) {
+                    item(key = "disc:$disc") { DiscHeader(disc, discTitle) }
                 }
                 lastDisc = disc
                 item(key = song.id) {
@@ -114,9 +120,12 @@ fun AlbumDetailScreen(
 }
 
 @Composable
-private fun DiscHeader(disc: Long) {
+private fun DiscHeader(
+    disc: Long,
+    title: String?,
+) {
     Text(
-        text = "Disc $disc",
+        text = title?.takeIf { it.isNotBlank() } ?: "Disc $disc",
         style = MaterialTheme.typography.titleLarge,
         color = MaterialTheme.colorScheme.onSurfaceVariant,
         modifier = Modifier.padding(start = 16.dp, end = 16.dp, top = 20.dp, bottom = 4.dp),

app/src/main/kotlin/com/subtracks/ui/library/AlbumDetailViewModel.kt

@@ -4,6 +4,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.CoverArtRef
+import com.subtracks.data.model.Disc
 import com.subtracks.data.model.Song
 import com.subtracks.data.repo.LibraryRepository
 import com.subtracks.data.repo.SourceRepository
@@ -28,6 +29,8 @@ class AlbumDetailViewModel(
 
     val songs: Flow<List<Song>> = sourceId.flatMapLatest { libraryRepository.albumSongs(it, albumId) }
 
+    val discs: Flow<List<Disc>> = sourceId.flatMapLatest { libraryRepository.albumDiscs(it, albumId) }
+
     fun coverArt(
         coverArt: String?,
         thumbnail: Boolean,

app/src/test/kotlin/com/subtracks/data/source/subsonic/SubsonicXmlTest.kt

@@ -60,6 +60,28 @@ class SubsonicXmlTest {
         assertEquals(12L, albums[0].songCount)
     }
 
+    @Test
+    fun mapsAlbumDiscTitles() {
+        val document =
+            parse(
+                """
+                <subsonic-response status="ok">
+                  <albumList2>
+                    <album id="al1" name="The Wall" artist="Pink Floyd" artistId="ar1" songCount="26">
+                      <discTitles disc="1" title="The Calm"/>
+                      <discTitles disc="2" title="The Storm"/>
+                      <discTitles disc="3" title=""/>
+                    </album>
+                  </albumList2>
+                </subsonic-response>
+                """.trimIndent(),
+            )
+
+        val albums = SubsonicXml.albums(1, document)
+
+        assertEquals(mapOf(1L to "The Calm", 2L to "The Storm"), albums.single().discTitles)
+    }
+
     @Test
     fun parsesTimestampsWithFractionsAndOffsets() {
         assertEquals(1789906657L, IsoDate.parse("2026-09-20T12:17:37.370827413Z"))

app/src/test/kotlin/com/subtracks/data/sync/SyncServiceTest.kt

@@ -204,6 +204,102 @@ class SyncServiceTest {
             assertEquals(5678L, stored?.starred)
         }
 
+    @Test
+    fun syncStoresAlbumDiscTitles() =
+        runTest {
+            insertSource()
+            val source =
+                FakeMusicSource(
+                    albums = listOf(album("al1").copy(discTitles = mapOf(1L to "The Calm", 2L to "The Storm"))),
+                )
+
+            SyncService(db, source).sync()
+
+            assertEquals(mapOf(1L to "The Calm", 2L to "The Storm"), storedDiscs("al1"))
+        }
+
+    @Test
+    fun syncClearsDiscTitlesWhenTheServerStopsSendingThem() =
+        runTest {
+            insertSource()
+            val source =
+                FakeMusicSource(
+                    albums = listOf(album("al1").copy(discTitles = mapOf(1L to "The Calm"))),
+                )
+
+            SyncService(db, source).sync()
+            assertEquals(mapOf(1L to "The Calm"), storedDiscs("al1"))
+
+            source.albums = listOf(album("al1"))
+
+            SyncService(db, source).sync()
+            assertEquals(emptyMap<Long, String>(), storedDiscs("al1"))
+        }
+
+    @Test
+    fun discTitlesAreKeptPerAlbum() =
+        runTest {
+            insertSource()
+            val source =
+                FakeMusicSource(
+                    albums =
+                        listOf(
+                            album("al1").copy(discTitles = mapOf(1L to "First Album Disc")),
+                            album("al2"),
+                        ),
+                )
+
+            SyncService(db, source).sync()
+
+            assertEquals(mapOf(1L to "First Album Disc"), storedDiscs("al1"))
+            assertEquals(emptyMap<Long, String>(), storedDiscs("al2"))
+        }
+
+    @Test
+    fun removingAnAlbumRemovesItsDiscTitles() =
+        runTest {
+            insertSource()
+            val source =
+                FakeMusicSource(
+                    albums =
+                        listOf(
+                            album("al1").copy(discTitles = mapOf(1L to "The Calm")),
+                            album("al2").copy(discTitles = mapOf(1L to "The Storm")),
+                        ),
+                )
+
+            SyncService(db, source).sync()
+
+            source.albums = listOf(album("al2").copy(discTitles = mapOf(1L to "The Storm")))
+
+            SyncService(db, source).sync()
+
+            assertEquals(emptyMap<Long, String>(), storedDiscs("al1"))
+            assertEquals(mapOf(1L to "The Storm"), storedDiscs("al2"))
+        }
+
+    @Test
+    fun syncUpdatesADiscTitle() =
+        runTest {
+            insertSource()
+            val source = FakeMusicSource(albums = listOf(album("al1").copy(discTitles = mapOf(1L to "Old"))))
+
+            SyncService(db, source).sync()
+            assertEquals(mapOf(1L to "Old"), storedDiscs("al1"))
+
+            source.albums = listOf(album("al1").copy(discTitles = mapOf(1L to "New")))
+
+            SyncService(db, source).sync()
+            assertEquals(mapOf(1L to "New"), storedDiscs("al1"))
+        }
+
+    private suspend fun storedDiscs(albumId: String): Map<Long, String> =
+        db
+            .libraryDao()
+            .discs(1, albumId)
+            .first()
+            .associate { it.disc to it.title }
+
     private suspend fun <T : Any> PagingSource<Int, T>.allRows(): List<T> {
         val page = load(PagingSource.LoadParams.Refresh(key = null, loadSize = 100, placeholdersEnabled = false))
         return (page as PagingSource.LoadResult.Page).data

app/src/test/kotlin/com/subtracks/ui/AlbumDiscsTest.kt

@@ -8,6 +8,7 @@ import androidx.compose.ui.test.onAllNodesWithText
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.github.takahirom.roborazzi.RobolectricDeviceQualifiers
 import com.subtracks.data.model.Album
+import com.subtracks.data.model.Disc
 import com.subtracks.data.model.Song
 import com.subtracks.ui.library.AlbumDetailScreen
 import com.subtracks.ui.theme.SubtracksTheme
@@ -32,6 +33,34 @@ class AlbumDiscsTest {
         assertEquals(1, nodesWithText("Disc 2"))
     }
 
+    @Test
+    fun discHeadersUseTheDiscTitleWhenPresent() {
+        setContent(
+            listOf(song("s-a", disc = 1, track = 1), song("s-b", disc = 2, track = 1)),
+            discs = listOf(disc(1, "The Calm"), disc(2, "The Storm")),
+        )
+        assertEquals(1, nodesWithText("The Calm"))
+        assertEquals(1, nodesWithText("The Storm"))
+        assertEquals(0, nodesWithText("Disc 1"))
+    }
+
+    @Test
+    fun discHeadersFallBackToTheDiscNumber() {
+        setContent(listOf(song("s-a", disc = 1, track = 1), song("s-b", disc = 2, track = 1)))
+        assertEquals(1, nodesWithText("Disc 1"))
+        assertEquals(1, nodesWithText("Disc 2"))
+    }
+
+    @Test
+    fun singleDiscAlbumShowsItsTitleWhenPresent() {
+        setContent(
+            listOf(song("s-a", disc = 1, track = 1), song("s-b", disc = 1, track = 2)),
+            discs = listOf(disc(1, "The Calm")),
+        )
+        assertEquals(1, nodesWithText("The Calm"))
+        assertEquals(0, nodesWithText("Disc 1"))
+    }
+
     @Test
     fun albumTracksShowTheirTrackNumbers() {
         setContent(listOf(song("s-a", disc = 1, track = 1), song("s-b", disc = 1, track = 2)))
@@ -51,12 +80,16 @@ class AlbumDiscsTest {
         assertEquals(0, nodesWithText("Disc 1"))
     }
 
-    private fun setContent(songs: List<Song>) {
+    private fun setContent(
+        songs: List<Song>,
+        discs: List<Disc> = emptyList(),
+    ) {
         composeRule.setContent {
             SubtracksTheme {
                 AlbumDetailScreen(
                     album = album(),
                     songs = songs,
+                    discs = discs,
                     coverArt = { _, _ -> null },
                     artwork = null,
                     onBack = {},
@@ -89,6 +122,11 @@ class AlbumDiscsTest {
         genre = null,
     )
 
+    private fun disc(
+        disc: Long,
+        title: String,
+    ) = Disc(sourceId = 1, albumId = "al-1", disc = disc, title = title)
+
     private fun album() =
         Album(
             sourceId = 1,