ModelForm.Meta.fields and exclude are not honoured for custom fields

[Tino de Bruijn]

​Selecting fields to use states that only form fields that are listed in Meta.fields or are not listed in Meta.exclude are used and "Any fields not included in a form by the above logic will not be set by the form’s save() method.".

But when I add a custom field, it is displayed and saved even when not included in fields or when excluded. Eg.:

class TestForm(forms.ModelForm):
    conditional_field = forms.TextField()

    class Meta:
        model = MyModel
        exclude = ('conditional_field',)

Still displays "conditional_field".

The reason I wanted to use this, is conditionally toggle the field in __init__. (Even if that is not the correct way to approach this, it still is unexpected behaviour)

[Hasan Ramezani]

The reason is these lines of code in class ModelFormMetaclass in django/forms/models.py file:

            # Override default model fields with any custom declared ones
            # (plus, include all the other declared fields).
            fields.update(new_class.declared_fields)

I Attached a patch and also i create a pull request to fix this bug.

[Tim Graham]

As far as I understand, this is by design. Please see the documentation added in #8620 for the rationale and open a discussion on the DevelopersMailingList if you disagree with the current decisions. Thanks!