Django: Ordering objects by their children's attributes

Question

Consider the models:

class Author(models.Model):
    name = models.CharField(max_length=200, unique=True)

class Book(models.Model):
    pub_date = models.DateTimeField()
    author = models.ForeignKey(Author)

Now suppose I want to order all the books by, say, their pub_date. I would use order_by('pub_date'). But what if I want a list of all authors ordered according to who most recently published books?

It's really very simple when you think about it. It's essentially:

• The author on top is the one who most recently published a book
• The next one is the one who published books not as new as the first,
• So on etc.

I could probably hack something together, but since this could grow big, I need to know that I'm doing it right.

Help appreciated!

Edit: Lastly, would the option of just adding a new field to each one to show the date of the last book and just updating that the whole time be better?

Answer 1

from django.db.models import Max
Author.objects.annotate(max_pub_date=Max('books__pub_date')).order_by('-max_pub_date')

this requires that you use django 1.1

and i assumed you will add a 'related_name' to your author field in Book model, so it will be called by Author.books instead of Author.book_set. its much more readable.