Added getSurveyForContent method to SurveyLogic.
This method returns a Survey for a given content. The backreferenceproperty will not work because of inheritance.
from django.core.management.base import NoArgsCommand
class Command(NoArgsCommand):
help = "Validates all installed models."
requires_model_validation = False
def handle_noargs(self, **options):
self.validate(display_num_errors=True)