Django annotation on field added with extra

Question

I'm trying to find a way to take an annotation over two fields on a model added together. Something like:

total_done = qs.values(
    'ability__ability_name',
).extra(
    select={
        'total_amount': 'effective_value + overage',
    }
).annotate(
    total=Sum('total_amount'),
).values(
    'ability__ability_name', 'total_amount'
).order_by('-total_amount')

The above doesn't work and yields the error "Cannot resolve keyword 'total_amount' into field" I already tried the solution indicated here: Using .aggregate() on a value introduced using .extra(select={...}) in a Django Query? However no luck still get the "Cannot resolve keyword 'total_amount' into field"

Anything other than performing the query in raw sql as the querystring that's being passed in could have various filters and excludes already performed on it making that prospect a little complicated. I'm also trying to avoid adding the field to the actual model and calculating it's value during save unless that's the only way.

Answer 1

I think its better to user annotation to get the total_amount value:

total_done = qs.values(
'ability__ability_name',
).annotate(
    total_amount=F('effective_value') + F('overage')
    total=Sum('total_amount'),
).values(
    'ability__ability_name', 'total_amount'
).order_by('-total_amount')

Answer 2

Try something like this:

total_done = qs.extra(select = {'total_amount': 'SUM(one_column + another_column)'}, )