class CarSearchForm(forms.Form):
# lots of fields like this
bodystyle = forms.ChoiceField(choices=bodystyle_choices())
Each choice is, e.g., ("Saloon", "Saloon (15 cars)")
. The choices are computed by this function:
def bodystyle_choices():
return [(bodystyle.bodystyle_name, '%s (%s cars)' %
(bodystyle.bodystyle_name, bodystyle.car_set.count()))
for bodystyle in Bodystyle.objects.all()]
My problem is the choices functions are getting executed every time I import my_forms.py
. I think this is due to the way Django declares its fields: in the class but not in a class method. Which is fine, but my views.py
imports my_forms.py
so the choices lookups are done on every request no matter which view is used.
I thought that maybe putting choices=bodystyle_choices
with no bracket would work, but I get:
'function' object is not iterable
Obviously I can use caching and put the import my_forms
just in the view functions required, but that doesn't change the main point: my choices need to be lazy!
You can use the lazy
function:
from django.utils.functional import lazy
class CarSearchForm(forms.Form):
# lots of fields like this
bodystyle = forms.ChoiceField(choices=lazy(bodystyle_choices, tuple)())
Very nice utility function!