Form Code getting executed during django project startup

Web Architect

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Oct 12, 2018, 3:52:31 AM10/12/18

to Django users

Hi,

We are using Django for our ecommerce site.

I have some confusion on when the code gets executed in Django. I have a django form with a choice field in module m1.py:

class SomeForm(forms.Form):

field = forms.ChoiceField(choices=get_choices())

def get_choices():

return some choices

In views.py, I have imported SomeForm:

from app.m1 import SomeForm

class SomeFormView(Formview):

form = SomeForm

...rest of the view code

When I run the django project using ./manage.py runserver, I am surprised to see that get_choices gets executed. This is undesirable as I can have a Django queryset in get_choices and I do not want unnecessary DB access.

It would be really helpful if someone can shed some light on the above and tell me what exactly is happening. How can I avoid get_choices getting executed during django start or running? get_choices should only get executed when SomeFormView is accessed.

Thanks.

Michal Petrucha

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Oct 12, 2018, 4:09:38 AM10/12/18

to Django users

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

On Fri, Oct 12, 2018 at 12:52:31AM -0700, Web Architect wrote:
> Hi,
>
> We are using Django for our ecommerce site.
>
> I have some confusion on when the code gets executed in Django. I have a
> django form with a choice field in module m1.py:
>
> class SomeForm(forms.Form):
> field = forms.ChoiceField(choices=get_choices())

The problem is here – you're calling get_choices, and passing the
result to the ChoiceField as a static list. If you pass get_choices as
a function, it will be called at runtime, whenever the form is
instantiated:

class SomeForm(forms.Form):
field = forms.ChoiceField(choices=get_choices)

Good luck,

Michal

>
>
> def get_choices():
> return some choices
>
>
> In views.py, I have imported SomeForm:
>
> from app.m1 import SomeForm
>
> class SomeFormView(Formview):
> form = SomeForm
> ...rest of the view code
>
>
> When I run the django project using ./manage.py runserver, I am surprised
> to see that get_choices gets executed. This is undesirable as I can have a
> Django queryset in get_choices and I do not want unnecessary DB access.
>
> It would be really helpful if someone can shed some light on the above and
> tell me what exactly is happening. How can I avoid get_choices getting
> executed during django start or running? get_choices should only get
> executed when SomeFormView is accessed.
>
> Thanks.

Web Architect

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Oct 12, 2018, 5:19:56 AM10/12/18

to Django users

Hi Michal,

Thanks a lot. That was an eye-opener and a big help :)

Thanks.

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