#27758: Template widget rendering breaks the AdvancedModelIterator pattern
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Reporter: Jon Dufresne | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 1.11
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Occasionally, when extending `ModelChoiceField` and
`ModelMultipleChoiceField` with a custom widget, it is useful for the
widget to know the object used to create the value, label pair. This could
be used to adding custom HTML attributes to very specific choices.
Historically, a pattern was developed to handle this situation named
[http://srcmvn.com/blog/2013/01/15/django-advanced-model-choice-field
AdvancedModelChoiceIterator]. The pattern described in the article breaks
in 1.11.
Firstly, `ChoiceWidget` now always expects a 2-tuple returned by
`ModelChoiceIterator.choice()` as it is unpacked in
[https://github.com/django/django/blob/a15d81a183e2d85969ed46adb975661515330b16/django/forms/widgets.py#L573
ChoiceWidget.optgroups()]. The usage is
[https://docs.djangoproject.com/en/1.10/ref/forms/fields/#django.forms.ChoiceField.choices
documented] as requiring a 2-tuple, so maybe this is considered OK.
An alternative I considered was returning a wrapped value to hold the
object, hoping this would be accessible from
`ChoiceWidget.create_option()`. Unfortunately this did not work as the
value is eagerly coerced to a string very early in
[https://github.com/django/django/blob/a15d81a183e2d85969ed46adb975661515330b16/django/forms/widgets.py#L577
ChoiceWidget.optgroups()]. For example:
{{{
class AdvancedChoiceValue:
def __init__(self, value, obj):
self.value = value
self.obj = obj
def __str__(self):
return str(self.value)
class AdvancedChoiceIterator(ModelChoiceIterator):
def choice(self, obj):
value, label = super().choice(obj)
return AdvancedChoiceValue(value, obj), label
}}}
I think delaying the `force_text()` until checking the selected value
would solve this problem.
--
Ticket URL: <https://code.djangoproject.com/ticket/27758>
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