Question

I have a Product model, with a one-to-many relation with a Rating model. I was previously storing an average_stars field in Product model, which I would update everytime a new Rating was added for that Product model. I would have a function in views.py which would return a QuerySet of all Product instances, ordered by average_star. Is there a way to do this more dynamically using a combination of .aggregate and .order_by, or anything along these lines.

In other words, is there a way to calculate the average for each product from all its respective Rating models, and sort them by that attribute? And which approach is better?

Answer 1

Assuming that your Rating model has a stars field, then you should use annotate:

from django.db.models import Avg
Product.objects.annotate(average_stars = Avg('rating__stars')).order_by('-average_stars')