formfield_for_choice_field() doesn't validate choices updated in method

[Robert <weglarek.robert+djangotrac@…>]

Having field declared in model:

element = models.CharField(max_length=500, verbose_name=_('admin element'), choices=(('foo', 'bar'),))

and that function in admin:

class AdminModuleElementInline(admin.StackedInline):
    model = AdminModuleElement
    def formfield_for_choice_field(self, db_field, request=None, **kwargs):
        if db_field.name == 'element':
            kwargs['choices'] = (
                ('accepted', 'Accepted'),
                ('denied', 'Denied'),
            )
        return db_field.formfield(**kwargs)

when I try to save it I get an error:
Value u'accepted' is not a valid choice.

So it updates the list, but validator checks the choices declared in model.

[anonymous]

any workaround for this issue ?

[Jannis Leidel]

Could you please provide a full traceback?

[Aymeric Augustin]

There is no traceback -- the validation error is displayed in the admin.

The reporter's example uses inlines. I could reproduce the issue with the following code. Screenshot attached.

# models.py

from django.db import models1

class Variable(models.Model):
    NAME_CHOICES = (
        ('foo', 'foo'),
        ('bar', 'bar'),
        ('baz', 'baz'),
    )
    name  = models.CharField(max_length=3, choices=NAME_CHOICES)

# admin.py

from django.contrib import admin
from .models import Variable

class VariableAdmin(admin.ModelAdmin):

    def formfield_for_choice_field(self, db_field, request, **kwargs):
        if db_field.name == "name":
            kwargs['choices'] = (
                ('quux', 'quux'),
                ('quuux', 'quuux'),
            )
        return super(VariableAdmin, self).formfield_for_choice_field(db_field, request, **kwargs)

admin.site.register(Variable, VariableAdmin)

---

I don't think it makes sense to allow in the form values that aren't allowed by the model. If I understand correctly this method can only be used to restrict changes, not to extend them. If that's true, it should be mentioned in the documentation of formfield_for_choice_field.

[Joeri Bekker]

The function name formfield_for_choice_field suggests that you are changing the form field, not the database field which is exactly what happens. The form field choices are updated, the model field choices are not, hence validation (on the model level) fails.

If you want flexible choices, define a CharField in your model without any choices argument. Create a form where you overwrite the widget for that CharField with a forms.Select . Then use the formfield_for_dbfield function (not the formfield_for_choice_field since it's not a choice field in the database model) and fill the kwargs['widget'].choices with your list of choices.

Example:

# models.py

from django.db import models1

class Variable(models.Model):
    name  = models.CharField(max_length=3)

# admin.py

from django import forms
from django.contrib import admin
from .models import Variable

class VariableForm(forms.ModelForm):
    class Meta:
        model = Variable
        widgets = {
            'name': forms.Select(),
        }

class VariableAdmin(admin.ModelAdmin):
    form = VariableForm

    def formfield_for_dbfield(self, db_field, **kwargs):
        if db_field.name == "name":
            kwargs['widget'].choices = (
                ('quux', 'quux'),
                ('quuux', 'quuux'),
            )
        return super(VariableAdmin, self).formfield_for_dbfield(db_field, **kwargs)

admin.site.register(Variable, VariableAdmin)

[Preston Holmes]

hitting an unrelated issue in some of this same code, and figured I'd address this. The best fix for now is to clarify that model choices and their validation always trump form choices.

There are a number of places where this can cause a trip up, but I'm going to go with a fix for this as a doc note.

[Preston Holmes <preston@…>]

In 10f8a2100279621ca0e0fa47d99ee744741a05e7:

Fixed #18168 -- clarified precedence of validation

any choices set by formfield_for_choice_field are still subject
to model validation of the model field's choices attribute