Django中使用group_by的方法

class Book(models.Model): 
   name = models.CharField(u'书名',max_length=255,db_index = True) 
   author = models.CharField(u'作者',max_length=255) 
   remark = models.CharField(u'备注',max_length=255) 
   pub_date = models.DateTimeField(u'发表时间',auto_now_add = True) 

book_list = Book.objects.all() 
book_list.query.group_by = ['author'] 

query = Book.objects.all().query 
query.group_by = ['author'] 
book_list = QuerySet(query = query, model = Book)