def set_sort(self, request):
        sort_request = request.GET.get(self.sort_parameter, self.default_sort)
        if sort_request.startswith('-'):
            sort_order = '-'
            sort_field = sort_request.split('-')[1]
        else:
            sort_order = ''
            sort_field = sort_request
        if not sort_field in self._allowed_sort_fields:
            sort_order = self.default_sort_order
            sort_field = self.default_sort_field
        return (sort_order, sort_field)