id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
9373	"""This field is required"" error even on empty inlines formsets in the admin model page, when hiding a choice field of a custom form."	tyrion.mx@…		"I have a custom Form for one of my models (in the example !SecondModel) that adds one choice field with an initial value.
If I use that model/form as an inline formset and I exclude the extra field using the ""fields"" attribute of the !ModelAdmin, I got ""This Field is required"" on all the forms of the formset, including those who where left blank. Here a simple example:
{{{
#!python
# models.py
from django.db import models

class FirstModel(models.Model):
    a = models.CharField(max_length=10)
    b = models.CharField(max_length=10)

class SecondModel(models.Model):
    link = models.ForeignKey(FirstModel)
    c = models.CharField(max_length=10)

# admin.py
from django.contrib import admin
from bug.bugged import models, forms

class SecondAdmin(admin.TabularInline):
    model = models.SecondModel
    form = forms.SecondForm
    fields = ['c']
    extra = 3

class FirstAdmin(admin.ModelAdmin):
    inlines = [SecondAdmin]
 
admin.site.register(models.FirstModel, FirstAdmin)

# forms.py
from django import forms
from bug.bugged import models

DUMMY_CHOICES = (
    (0, 'a'),
    (1, 'b'),
    (2, 'c')
)

class SecondForm(forms.ModelForm):
    d = forms.IntegerField(label='d', initial=0, widget=forms.Select(choices=DUMMY_CHOICES))
    class Meta:
        model = models.SecondModel
}}}

The problem is {{{fields = ['c']}}}, commenting out that line I get no errors.
I guess, this is beacuse of the {{{has_changed}}} check, called by the {{{full_clean}}} method of {{{forms.Form}}}. It happens that {{{changed_data}}} compares the initial ""d"" value that had been set to 0 with the result of ""field.widget.value_from_datadict(self.data,..."" that is None because we have not a key for ""d"" in self.data. So changed_data will contain ""d"" even if the form has not been changed.

From django/forms/forms.py
{{{
#!python
                prefixed_name = self.add_prefix(name)
                data_value = field.widget.value_from_datadict(self.data, self.files, prefixed_name)
                if not field.show_hidden_initial:
                    initial_value = self.initial.get(name, field.initial)

}}}
"	Bug	new	contrib.admin	1.7	Normal		admin, inlines		Accepted	0	0	0	0	0	0