class Author (models.Model):
  name = models.CharField (max_length = 255)
  born = models.DateField (null = True, blank = True)
  died = models.DateField (null = True, blank = True)
  bio = models.TextField (null = True, blank = True)

    def __unicode__ (self):
      return self.name

    class Meta:
      ordering = ["name"]

class Book (models.Model):
    name = models.CharField (max_length = 255)
    date = models.DateField ()
    authors = models.ManyToManyField (Author, related_name = "books")
    description = models.TextField (null = True, blank = True)

    def __unicode__ (self):
        authors = [author.name for author in self.authors.all ()]
        return ", ".join (authors) + ": "  + self.name

    class Meta:
        ordering = ["name", "date"]