从Django模型中的manytomany字段获取值?

我得吃饭了

class Book(models.Model):
    title = models.CharField(max_length=200)        
    authors = models.ManyToManyField(Individual, related_name="author_for", blank=True, null=True)
    illustrators = models.ManyToManyField(Individual, related_name="illustrator_for", blank=True, null=True)

class Unitary_Sale(models.Model):        
            book = models.ForeignKey(Book)
            quantity = models.IntegerField()
            unit_price = models.DecimalField(max_digits=15, decimal_places=3)
            sale = models.ForeignKey(Sale)

报告书是如何被作者或插画家出售的?

by_author = {}
   for unit_sale in Unitary_sale.objects.all():
        author = unit_sale.book.authors
        by_authors[author] =  (unit_sale.quantity, unit_sale.quantity *unit_sale.unit_price)


Author   Qty  Amount($)
A        2     20
A&B      3     30

一本书有很多作者