Commit 9fb0f5dd authored by Marc Tamlyn's avatar Marc Tamlyn
Browse files

Fixed #22510 -- Harden field removal to only None. 

Refs #8620.

If we allow any value to remove form fields then we get name clashes
with method names, media classes etc. There was a backwards
incompatibility introduced meaning ModelForm subclasses with declared
fields called media or clean would lose those fields.

Field removal is now only permitted by using the sentinel value None.
The docs have been slightly reworded to refer to removal of fields
rather than shadowing.

Thanks to gcbirzan for the report and initial patch, and several of the
core team for opinions.
parent f47e226f

django/forms/forms.py

+2 −2
Original line number Diff line number Diff line
@@ -92,8 +92,8 @@ class DeclarativeFieldsMetaclass(MediaDefiningClass): 
                declared_fields.update(base.declared_fields)



            # Field shadowing.

            for attr in base.__dict__.keys():

                if attr in declared_fields:

            for attr, value in base.__dict__.items():

                if value is None and attr in declared_fields:

                    declared_fields.pop(attr)



        new_class.base_fields = declared_fields

docs/ref/forms/api.txt

+14 −4
Original line number Diff line number Diff line
@@ -982,10 +982,20 @@ classes:: 


.. versionadded:: 1.7



* It's possible to opt-out from a ``Field`` inherited from a parent class by

  shadowing it. While any non-``Field`` value works for this purpose, it's

  recommended to use ``None`` to make it explicit that a field is being

  nullified.

* It's possible to declaratively remove a ``Field`` inherited from a parent

  class by setting the name to be ``None`` on the subclass. For example::



    >>> from django import forms



    >>> class ParentForm(forms.Form):

    ...     name = forms.CharField()

    ...     age = forms.IntegerField()



    >>> class ChildForm(ParentForm):

    ...     name = None



    >>> ChildForm().fields.keys()

    ... ['age']



.. _form-prefix:

docs/releases/1.7.txt

+2 −2
Original line number Diff line number Diff line
@@ -544,8 +544,8 @@ Forms 
  inheriting from both ``Form`` and ``ModelForm`` simultaneously have been

  removed as long as ``ModelForm`` appears first in the MRO.



* It's now possible to opt-out from a ``Form`` field declared in a parent class

  by shadowing it with a non-``Field`` value.

* It's now possible to remove a field from a ``Form`` when subclassing by

  setting the name to ``None``.



* The new :meth:`~django.forms.Form.add_error()` method allows adding errors

  to specific form fields.

docs/topics/forms/modelforms.txt

+2 −4
Original line number Diff line number Diff line
@@ -666,10 +666,8 @@ There are a couple of things to note, however. 


.. versionadded:: 1.7



* It's possible to opt-out from a ``Field`` inherited from a parent class by

  shadowing it. While any non-``Field`` value works for this purpose, it's

  recommended to use ``None`` to make it explicit that a field is being

  nullified.

* It's possible to declaratively remove a ``Field`` inherited from a parent class by

  setting the name to be ``None`` on the subclass.



  You can only use this technique to opt out from a field defined declaratively

  by a parent class; it won't prevent the ``ModelForm`` metaclass from generating

tests/model_forms/tests.py

+19 −1
Original line number Diff line number Diff line
@@ -2227,7 +2227,7 @@ class ModelFormInheritanceTests(TestCase): 


        self.assertEqual(list(ModelForm().fields.keys()), ['name', 'age'])



    def test_field_shadowing(self):

    def test_field_removal(self):

        class ModelForm(forms.ModelForm):

            class Meta:

                model = Writer
@@ -2250,6 +2250,24 @@ class ModelFormInheritanceTests(TestCase): 
        self.assertEqual(list(type(str('NewForm'), (ModelForm, Form, Mixin), {})().fields.keys()), ['name', 'age'])

        self.assertEqual(list(type(str('NewForm'), (ModelForm, Form), {'age': None})().fields.keys()), ['name'])



    def test_field_removal_name_clashes(self):

        """Regression test for https://code.djangoproject.com/ticket/22510."""



        class MyForm(forms.ModelForm):

            media = forms.CharField()



            class Meta:

                model = Writer

                fields = '__all__'



        class SubForm(MyForm):

            media = None



        self.assertIn('media', MyForm().fields)

        self.assertNotIn('media', SubForm().fields)

        self.assertTrue(hasattr(MyForm, 'media'))

        self.assertTrue(hasattr(SubForm, 'media'))





class StumpJokeForm(forms.ModelForm):

    class Meta: