GeometryField does not allow setting blank=True and null=False

[Paul Winkler]

Sometimes you want to populate a required field's missing value with a value generated eg. from other form fields.
One common idiom for doing this is to have SomeField(blank=True, null=False) and provide the missing value in eg. the Form's clean() method.

For example, I've done variations on this a lot:

class Foo(Model):
    geom = PointField(blank=True, null=False)
    address = CharField(max_length=100)
    class Meta:
        app_label = 'myblock' # or whatever,

class FooForm(ModelForm):
    class Meta:
        model = Foo

    def clean(self):
        geom = self.cleaned_data.get('geom')
        if not geom:
            self.cleaned_data['geom'] = geocode(self.cleaned_data['address'])
        return super(FooForm, self).clean()

But with a GeometryField, that doesn't work, because of these lines in
GeometryField.clean() in django/contrib/gis/forms/fields.py :

        if not value:
            if self.null and not self.required:
                # The geometry column allows NULL and is not required.
                return None
            else:
                raise forms.ValidationError(self.error_messages['no_geom'])

Effectively, this makes blank=True meaningless.

As far as I know, GeometryField is the only FormField shipped with django that behaves this way.
This is surprising and inconsistent, and leads to odd workarounds to convince forms.GeometryField to leave you alone. Eg. hacking a ModelAdmin's formfield_for_dbfield() like so:

    def formfield_for_dbfield(self, db_field, **kwargs):
        if db_field.name == 'geom':
            kwargs['required'] = False
            kwargs['null'] = True
        return super(MyModelAdmin, self).formfield_for_dbfield(db_field, **kwargs)

Fixing this is trivial. Patch attached.

[Paul Winkler]

second attempt patch to fix 16610, with test. a typo fixed

[Aymeric Augustin]

Note that #15271 is also about GeometryField.clean().

Something should be done about the first comment in the patch: # Never checked: stop passing this? => needs improvement.

[Paul Winkler]

Yep, raising that on the dev list now... ​https://groups.google.com/group/django-developers/browse_thread/thread/9383c62827edc167

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Claude Paroz]

Updated patch

[Claude Paroz]

Just attached an updated patch, with some other choices, but basically the same effect (hopefully). I choose a quick deprecation timeline for the null argument, because this is mostly undocumented stuff.

[Claude Paroz <claude@…>]

In 18e990fa9639b5476b556c8de82717ebfc8b254e:

Fixed #16110 -- Fixed GeometryField odd behaviour regarding null values

Thanks slinkp for the report and the initial patch.