code: def _delete_widget_content(sender, instance, **kwargs):
      
      if not issubclass(sender, WidgetContentModel):
          return
  
      # delete WidgetContent Entry
      wcs = WidgetContent.objects.filter(
          content_pk=instance.pk,
          content_model=('%s' % instance.__class__).replace("<class '", '').replace("'>", ''))
      for wc in wcs:
          logger.debug('delete wc %r'%wc)
          wc.delete()
docs: delete the widget content instance when a WidgetContentModel is deleted