def list_songs
    Song.all.sort{|song1,song2| song1.name<=>song2.name}.each_with_index{|song,i| puts (i+1).to_s+'. '+song.artist.name+' - '+song.name+' - '+song.genre.name }
end
def list_artists
    Artist.all.sort{|artist1,artist2| artist1.name<=>artist2.name}.each_with_index{|artist,i| puts (i+1).to_s+'. '+artist.name}
end
def list_genres
    Genre.all.sort{|genre1,genre2| genre1.name<=>genre2.name}.each_with_index{|genre,i| puts (i+1).to_s+'. '+genre.name}
end