python - Django order_by sum of fields

Question

Is it possible to use the django ORM to order a queryset by the sum of two different fields?

For example, I have a model that looks like this:

class Component(models.Model):
    material_cost = CostField()
    labor_cost = CostField()

and I want to do something like this:

component = Component.objects.order_by(F('material_cost') + F('labor_cost'))[0]

But unfortunately, F objects don't seem to work with 'order_by'. Is such a thing possible with django?

Answer 1

You can use extra for this.

Component.objects.extra(
    select={'fieldsum':'material_cost + labor_cost'},
    order_by=('fieldsum',)
)

See the documentation.