In Django forms.ModelChoiceField HOWTO restrict displayed choices but set one of the restricted values during cleanup

Question

I have a custom field which subclasses ModelMultipleChoiceField. I provide the choices to be displayed via queryset parameter. This queryset excludes certain values. My problem comes when during cleanup operation for some workflows I need to select an option which was initially excluded by the way of queryset. When I try to save this value django refuses to save it saying that it is not a valid option. On looking up the clean method for ModelMultipleChoiceField I found that it checks if the provided "value" is from within the initial queryset, which causes my dilemma.

I wanted to know if it is possible to circumvent this problem without any major hacks.

It sounds to me as though the field is doing exactly what you told it to. — Ignacio Vazquez-Abrams, Jul 08 '11 at 21:27
Right, but in one of the edge cases I need to make sure that at least some value is saved, which happens to be an erstwhile excluded choice value. — Chantz, Jul 08 '11 at 21:29

score 2 · Accepted Answer · answered Jul 08 '11 at 22:46

django/forms/models.py:1011 has this:

qs = self.queryset.filter(**{'%s__in' % key: value})

So it seems that if you overrode your custom field's clean() method to modify self.queryset as necessary before calling super(MyField, self).clean(value), you could handle this edge case relatively cleanly.

In Django forms.ModelChoiceField HOWTO restrict displayed choices but set one of the restricted values during cleanup

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