old_contents: from django import forms
  
  from adhocracy4.categories import models as category_models
  
  from . import models
  
  
  class IdeaForm(forms.ModelForm):
  
      def __init__(self, *args, **kwargs):
          module = kwargs.pop('module')
          super().__init__(*args, **kwargs)
          queryset = category_models.Category.objects.filter(module=module)
          self.fields['category'] = forms.ModelChoiceField(
              queryset=queryset,
              empty_label=None,
              required=False,
          )
  
      def show_categories(self):
          module_has_categories = len(self.fields['category'].queryset) > 0
          return module_has_categories
  
      class Meta:
          model = models.Idea
          fields = ['name', 'description', 'category']
  
new_contents: from adhocracy4.categories import forms as category_forms
  
  from . import models
  
  
  class IdeaForm(category_forms.CategorizableForm):
  
      class Meta:
          model = models.Idea
          fields = ['name', 'description', 'category']
  
subject: use categoribale for from core