public ActionResult <List <UserInterfaceObjects.SoundFile> > GetSoundFiles(
            [FromRoute] Guid playListId)
        {
            var userId = User.GetUserId();

            var soundFiles = _playListService
                             .GetFavoritesSoundFiles(userId)
                             .ToUserInterfaceObjects();

            _libraryService.ProcessIsFavoriteFlag(User.GetUserId(), soundFiles);

            return(Ok(soundFiles));
        }