Product of two fields annotation

Question

I currently have a line in my Django app like this:

db.execute(\"SELECT SUM(price * qty) FROM inventory_orderline WHERE order_id = %s\", [self.id])


        

Answer 1

Unfortunately, there aren't enough inbuilt Aggregate functions and specifically, there is not one for Product.

But that doesn't limit you in any way other than having to write a "non-concise" ORM query. Specifically for your case, you should be able to do:

self.line_items.extra(select=("lineprice": "orderline__price*orderline__qty")).aggregate(Sum('lineprice'))

Answer 2

It's not clearly documented, but this can be done with the F() function:

from django.db.models import F

self.line_items.annotate(lineprice=F('orderline__price') * F('orderline__qty')).aggregate(Sum('lineprice'))