app\models\Artist::getContributedSongs PHP 메소드

    public function getContributedSongs()
    {
        return Song::whereContributingArtistId($this->id)->get();
    }

 protected function fromArtist(Artist $artist)
 {
     // Don't forget the contributed songs.
     $songs = $artist->songs->merge($artist->getContributedSongs());
     return $this->fromMultipleSongs($songs);
 }