'save the draft revision and return the draft revision'

def save(self, request):

    creator = request.user
    doc_data = self.cleaned_data
    parent_doc = doc_data['based_on'].document
    locale = request.LANGUAGE_CODE
    (draft, created) = DraftRevision.objects.update_or_create(creator=creator, document=parent_doc, locale=locale, defaults=doc_data)
    return draft
