Subtracting two annotated columns

Question

I need to be able to sort on the aggregate of two annotated columns

So I\'d like to do something like this:

c = c.annotate(metric=Sum(\'results__metr         


        

Answer 1

Actually,

c = c.annotate(variance=F('metric')-F('metric_prior'))

works as you would like it to starting with Django 1.8.

Moreover, you can also order by an expression, which means you can just use:

c = c.order_by(F('metric') - F('metric_prior'))

or even just:

c = c.order_by(Sum('results__metric') - Sum('results__metric_prior'))