Django - How to annotate QuerySet using multiple field values?

I have a model called "Story" that has two integer fields called "views" and "votes". When I retrieve all the Story objects I would like to a开发者_StackOverflow社区nnotate the returned QuerySet with a "ranking" field that is simply "views"/"votes". Then I would like to sort the QuerySet by "ranking". Something along the lines of...

Story.objects.annotate( ranking=CalcRanking('views','votes') ).sort_by(ranking)

How can I do this in Django? Or should it be done after the QuerySet is retrieved in Python (like creating a list that contains the ranking for each object in the QuerySet)?

Thanks!

PS: In my actual program, the ranking calculation isn't as simple as above and depends on other filters to the initial QuerySet, so I can't store it as another field in the Story model.

In Django, the things you can pass to annotate (and aggregate) must be subclasses of django.db.models.aggregates.Aggregate. You can't just pass arbitrary Python objects to it, since the aggregation/annotation actually happens inside the database (that's the whole point of aggregate and annotate). Note that writing custom aggregations is not supported in Django (there is no documentation for it). All information available on it is this minimal source code: https://code.djangoproject.com/browser/django/trunk/django/db/models/aggregates.py

This means you either have to store the calculations in the database somehow, figure out how the aggregation API works or use raw sql (raw method on the Manager) to do what you do.