from datetime import date
from pony.orm import *

db = Database("sqlite", "lyrics.sqlite", create_db=True)

class Artist(db.Entity):
    name = Required(unicode)
    songs = Set("Song")

class Song(db.Entity):
    artists = Set(Artist)
    name = Required(unicode)
    done = Optional(date)
    youtube = Optional(unicode)
    lyric = Required("Lyric")

class Lyric(db.Entity):
    text = Required(LongUnicode)
    song = Required(Song)