Ability to SUM multiple columns

Is your feature request related to a problem? Please describe. I’d like to be able to use the Sum function over multiple columns.

Example for a model

class Stats(Model):
    one_column = fields.IntField(default=0)
    two_column = fields.IntField(default=0)

I’d like to be able to do run a query like select sum(one_column+two_column) from stats

Describe the solution you’d like Stats.annotate(total_sum=Sum('one_column+two_column')) (or something similar)

Additional context

Pypika can already resolve this as seen in this test:

https://github.com/kayak/pypika/blob/16339f85ed871d937609e9dbe26487b382ca5211/pypika/tests/test_formats.py

fn.Sum(self.table_abc.fizz + self.table_abc.buzz)

[lntuition]

@grigi Thank you so much for your discussion. I will make PR with 1 (but i’m not sure that i’m doing good. i will make WIP PR soon. Review that PR plz!) As you said, we need to think more carefully about 2 and 4.

[grigi]

Yes, source_param is a prime example where we want a Model to be different compared to a legacy DB column name.

We should definitly allow F expressions in annotations. And the inverse, of annotations in .update(...) operations as well. Maybe we can get away by just making Function aware of F expressions?