我可以在__unicode__中使用ForeignKey吗？

class Author(models.Model):
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return self.name

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

    def get_author_name(self):
        return self.author.name

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

    def __str__(self):
        return self.title + ' by ' + self.author.name