Opened 4 years ago

Last modified 7 months ago

#13181 new New feature

ChoiceField.choices need to accept callable, not only list or tuple

Reported by: mariarchi Owned by:
Component: Forms Version: 1.2-beta
Severity: Normal Keywords: ChoiceField, choices
Cc: admin@…, t.zander@…, someuniquename@… Triage Stage: Accepted
Has patch: yes Needs documentation: yes
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no



The subject pretty much describes all of it. If 'initial' can be a
callable, why 'choices' can't? Writing custom function is way more
convenient then altering init method of the model.

Attachments (5)

patch.diff (1.6 KB) - added by mariarchi 4 years ago.
as_actual_callable.diff (2.6 KB) - added by vanschelven 17 months ago.
with_callable_choice_iterator.diff (2.7 KB) - added by vanschelven 17 months ago.
full_version.diff (5.3 KB) - added by vanschelven 17 months ago.
with_field_as_param.diff (3.0 KB) - added by vanschelven 17 months ago.

Download all attachments as: .zip

Change History (28)

comment:1 Changed 4 years ago by mariarchi

  • Needs documentation unset
  • Needs tests set
  • Patch needs improvement unset

I would've written up tests, but I didn't really get how to add methods to regression tests - all functions have numbers - do you have to rename everything below inserted one?

comment:2 Changed 4 years ago by Alex

No, the numbers on the test objects are fairly arbitrary, feel free to name you TestCase methods more semantic.

comment:3 Changed 4 years ago by mrts

It's still important to check if the result can be converted to a list:

if callable(value):
    value = value()
value = list(value)

Changed 4 years ago by mariarchi

comment:4 Changed 4 years ago by mariarchi

@mrts: thx, updated the patch

comment:5 Changed 4 years ago by mariarchi

  • Needs tests unset

...and tests

comment:6 Changed 4 years ago by russellm

  • Triage Stage changed from Unreviewed to Accepted

comment:7 Changed 3 years ago by lukeplant

  • Type set to New feature

comment:8 Changed 3 years ago by lukeplant

  • Severity set to Normal

comment:9 Changed 3 years ago by julien

  • Needs documentation set

comment:10 Changed 3 years ago by julien

  • Easy pickings unset

#15950 is a dupe and has a patch with a different approach.

comment:11 follow-up: Changed 2 years ago by aaugustin

  • UI/UX unset

Change UI/UX from NULL to False.

comment:12 in reply to: ↑ 11 Changed 22 months ago by t.zander@…

  • Cc t.zander@… added

I'm interested in this, what's the status of it?

comment:13 Changed 18 months ago by vanschelven

I'll probably look into it in the upcoming sprint in Utrecht (Feb 23rd 2013).
Notes if anyone's picking it up before that:

The comment made by mrts ( is (as far as I understand it) not a good idea. As far as I understand it he/she is talking about evaluating the callable at field-definition time as well as when the form is actually initialized using form = MyForm().

But this is exactly one of the problems I'm dealing with: on form definition time the callable that is bound to choices may not have a meaningful result. It may be erratic (because it fetches results over the internet or depends on a database that is sometimes offline). If you have such a callable it will crash the whole application in the current situation and the situation proposed by mtrs.

My 2 cents.

comment:14 Changed 17 months ago by vanschelven

  • Owner changed from nobody to vanschelven
  • Status changed from new to assigned

Changed 17 months ago by vanschelven

comment:15 Changed 17 months ago by vanschelven

Attached (as_actual_callable.diff) is a super-ugly solution to what I consider the "real problem". Please see this as a starting point for further discussion.

The earlier patch basically evaluated the callable on-field-definition, i.e. once. The whole purpose of using a callable is to lazily evaluate so that was not an acceptible solution.

I noticed ModelChoiceField had this problem solved (as opposed to the regular ChoiceField), i.e. for each instance of a form the field's choices are freshly looked up in the queryset. In that case, they've made it work by patching __deepcopy__ (which is called when a form is instantiated) to change the widget's choices every time.

See this solution here:

My solution does something similar: on deepcopy the actual evaluation is done. Note also the fact that the widget's choices have to be manually set to an actual value, which happens in _set_choices()

Note that I use a different attribute to store the callable version of the choices. I hardly dare to call this elegant, but the amount of places there's dependencies on the fact that choices is an iterator is rather huge. Putting the callable version of choices in a different location makes sure we can dance around those issues.

comment:16 Changed 17 months ago by vanschelven

  • Owner vanschelven deleted
  • Status changed from assigned to new

comment:17 Changed 17 months ago by expleo

I managed to get it working this way:

Changed 17 months ago by vanschelven

comment:18 Changed 17 months ago by vanschelven

This approach (with_callable_choice_iterator.diff) is a prettier way to wrap the callable. The attached diff is the minimal way to get this issue fixed; I'll further look in to ways that combine it with:

  • Refactoring CallableChoiceIterator and ModelChoiceIterator to be of a common base class
  • We may want to consider passing field to the callable so that the callable has a bit more context. I'll play a bit with it.

Changed 17 months ago by vanschelven

Changed 17 months ago by vanschelven

comment:19 Changed 17 months ago by vanschelven

Comments on the recent patches:

  • I'm not a fan of the "refactoring" using the delegate presented in "full_version". The commonalities are simply not worth the refactoring.
  • I do like the version where the field is sent as a param; but whether that's actually useful is DDN.

comment:20 Changed 17 months ago by expleo

Updated pull request with with_field_as_param.diff:

comment:21 Changed 17 months ago by expleo

  • Triage Stage changed from Accepted to Design decision needed

comment:22 Changed 16 months ago by apollo13

  • Triage Stage changed from Design decision needed to Accepted

Moving back to "Accepted" since the ticket per se is accepted and we are dropping DDN.

comment:23 Changed 7 months ago by Fak3

  • Cc someuniquename@… added

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