implement SortableListView.get_ordering()
implement SortableListView.get_ordering()

see https://docs.djangoproject.com/en/1.10/ref/class-based-views/mixins-multiple-object/#django.views.generic.list.MultipleObjectMixin.get_ordering

liqd/adhocracy4,liqd/adhocracy4,liqd/adhocracy4,liqd/adhocracy4