excluded fields on ModelForm does not work on inherited fields

[Ben Davis]

When you have a ModelForm subclass, any fields in the exclude array are still included on the form if the field is part of the parent class. This happens in ModelFormMetaClass.__new__ when the class overrides new_class.base_fields with the parent fields *after* applying the exclusions.

[Ola Sitarska]

Together with Baptiste and Loic I managed to reproduce that, but we've decided that this is an expected behaviour. It only happens when you actually declare a field in a model form:

from django import forms

from .models import SampleModel

class BaseForm(forms.ModelForm):
    number = forms.CharField()

    class Meta:
        model = SampleModel

class SubclassForm(BaseForm):

    class Meta(BaseForm.Meta):
        exclude = ['number',]

Then you can see a number field in the form, but it doesn't get saved. Should I document it somewhere?

[Danilo Bargen]

This would be the test to reproduce the issue:

tests/model_forms/tests.py

@@ -473 +473 @@
     def test_subclassmeta_form(self):
         class SomeCategoryForm(forms.ModelForm):
             checkbox = forms.BooleanField()
+            othertext = forms.CharField()
 
             class Meta:
                 model = Category
@@ -483 +484 @@
             list.
             """
             class Meta(SomeCategoryForm.Meta):
-                exclude = ['url']
+                exclude = ['url', 'othertext']
 
         self.assertHTMLEqual(
             str(SubclassMeta()),

What's the reasoning for considering this intentional?

[Tim Graham]

I think the documentation was added in #8620, but perhaps it needs further clarification?

[Tim Graham]

Closing as duplicate unless reporter can provide additional information as to why the current documentation is insufficient (I'd guess he probably didn't see it).