实现数据库级联删除

internal/repository/library.go

@@ -78,8 +78,41 @@ func (r *LibraryRepository) UpdatePath(id int, path string) error {
 }
 
 func (r *LibraryRepository) Delete(id int) error {
-	_, err := r.db.Exec("DELETE FROM libraries WHERE id = ?", id)
-	return err
+	tx, err := r.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	// Delete the library — CASCADE removes media_files and songs automatically
+	_, err = tx.Exec("DELETE FROM libraries WHERE id = ?", id)
+	if err != nil {
+		return err
+	}
+
+	// Clean up orphan albums (no songs reference them)
+	_, err = tx.Exec(`
+		DELETE FROM albums WHERE id NOT IN (
+			SELECT DISTINCT album_id FROM songs WHERE album_id IS NOT NULL
+		)
+	`)
+	if err != nil {
+		return err
+	}
+
+	// Clean up orphan artists (no songs and no albums reference them)
+	_, err = tx.Exec(`
+		DELETE FROM artists WHERE id NOT IN (
+			SELECT DISTINCT artist_id FROM songs WHERE artist_id IS NOT NULL
+			UNION
+			SELECT DISTINCT artist_id FROM albums WHERE artist_id IS NOT NULL
+		)
+	`)
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit()
 }
 
 func (r *LibraryRepository) GetSongsByLibraryWithDetails(libraryID int) ([]SongDetail, error) {

internal/repository/media_repo.go

@@ -12,15 +12,11 @@ func NewMediaRepository(db *sql.DB) *MediaRepository {
 
 func (r *MediaRepository) Get(id int) (MediaFile, error) {
 	var m MediaFile
-	rows, err := r.db.Query("SELECT id, path, library_id FROM media_files WHERE id = ?", id)
+	err := r.db.QueryRow("SELECT id, path, library_id FROM media_files WHERE id = ?", id).Scan(
+		&m.ID, &m.Path, &m.LibraryID,
+	)
 	if err != nil {
 		return MediaFile{}, err
 	}
-	defer rows.Close()
-	if rows.Next() {
-		if err := rows.Scan(&m.ID, &m.Path, &m.LibraryID); err != nil {
-			return MediaFile{}, err
-		}
-	}
 	return m, nil
 }

internal/repository/song_repo.go

@@ -55,13 +55,11 @@ func (r *SongRepository) GetAllWithDetails() ([]SongDetail, error) {
 
 func (r *SongRepository) Get(id int) (Song, error) {
 	var song Song
-	rows, err := r.db.Query("SELECT id, title, artist_id, album_id, duration, media_file_id FROM songs WHERE id = ?", id)
+	err := r.db.QueryRow("SELECT id, title, artist_id, album_id, duration, media_file_id FROM songs WHERE id = ?", id).Scan(
+		&song.ID, &song.Title, &song.ArtistID, &song.AlbumID, &song.Duration, &song.MediaFileID,
+	)
 	if err != nil {
 		return Song{}, err
 	}
-	defer rows.Close()
-	if rows.Next() {
-		rows.Scan(&song.ID, &song.Title, &song.ArtistID, &song.AlbumID, &song.Duration, &song.MediaFileID)
-	}
 	return song, nil
 }