Allow override of hardcoded defaults in model Field.formfield()

[James Pic]

Currently, the model field builds the default form field that's used
by the modelform metaclass in Field.formfield(). It uses hardcoded defaults which it would be nice to be able to override with attributes.

Example patch: ​https://github.com/jpic/django/commit/d102f362f3c1ceaf2d5224d71f788c0821a481ae

This patch allows to use Radio widget by default for a OneToOne field:

    class TestModel(models.Model):
        name = models.CharField(max_length=200)

        test = models.OneToOneField(
            'self',
            null=True,
            blank=True,
            related_name='related_test_models',
            # This seems like it would always be useful
            formfield_defaults={
                'widget': forms.RadioSelect
            }
        )

[Tim Graham]

I'm not sure whether or not to accept this, so I raised it ​on the django-developers mailing list.

[Thomas Güttler]

I guess I understood what you want.

I see this problem: A django projects is a container for N apps.

Since there are N apps, and not just one: Who is allowed to provide defaults?

Yes, we already do change the default widgets. We use monkey patching: We modify the django classes. That is not a nice way, but works.

Yes, I would like to have an official solution, too.

[James Pic]

PR: ​https://github.com/django/django/pull/7723

[James Pic]

I'm unsure if I wouldn't prefer to just be able to define a project-level default formfield callback, because that's going to depend on what the INSTALLED_APPS provide. Then for example, to make all relations to Foo a particular widget instead of Select, and to make all CharFields have a text field:

# settings.py:
DEFAULT_FORMFIELD='project.forms.project_formfield'

# project/forms.py
def project_formfield(db_field, form_class, defaults):
    if db_field.rel.to == Foo:
        defaults['widget'] = forms.RadioSelect
        
    if db_field.model == Foo and isinstance(db_field, models.CharField):
        defaults['widget'] = forms.Textarea

    return form_class(**defaults)

This seems even more powerful, I've updated the PR to match this.

[James Pic]

This has been ​implemented in a third party, while not relying on supported APIs, remains sufficiently short (35 SLOCs) to be maintenable.