Make a field required if another field is marked on a Django form

Question

I have a model like this:

class News(models.Model):
    is_activity = models.BooleanField(default=False)
    activity_name = models.CharField(max_length=240, blank=True, null=True)

What I am trying to achieve, if is_activityverified, I want to activity_namebe required. Thus, I am trying to override the method __init__:

class NewsForm(forms.ModelForm):
    class Meta:
        model = News

    def __init__(self, *args, **kwargs):
        super(NewsForm, self).__init__(*args, **kwargs)
        if self.fields['is_activity'] is True:
            self.fields['activity_name'].required = True


class NewsAdmin(FrontendEditableAdminMixin, admin.ModelAdmin):
    form = NewsForm

Even if I check is_activity, activity_nameit is not required. What's wrong?

Answer 1

The method ModelForm.clean()gives you access to cleared data - here you can include conditional logic specific to the field:

from django.core.validators import EMPTY_VALUES

class NewsForm(forms.ModelForm):
    class Meta:
        model = News

    def clean(self):
        is_activity = self.cleaned_data.get('is_activity', False)
        if is_activity:
            # validate the activity name
            activity_name = self.cleaned_data.get('activity_name', None)
            if activity_name in EMPTY_VALUES:
                self._errors['activity_name'] = self.error_class([
                    'Activity message required here'])
        return self.cleaned_data

class NewsAdmin(FrontendEditableAdminMixin, admin.ModelAdmin):
    form = NewsForm