public bool MarkTrackAsPlayed(long id, long playlistId)
{
var playlist = context.Playlists.Include(p=>p.PlaylistTracks).Single(p => p.Id == playlistId);
var track = playlist.PlaylistTracks.Single(t => t.Id == id);
if (track == null) return false;
track.PlayedAt = DateTime.Now;
context.Entry(track).State = EntityState.Modified;
context.SaveChanges();
return true;
}