def remove_invalid_fields(self, queryset, fields, view):
        """Remove invalid fields from an ordering.

        Overwrites the DRF default remove_invalid_fields method to return
        both the valid orderings and any invalid orderings.
        """

        valid_orderings = []
        invalid_orderings = []

        # for each field sent down from the query param,
        # determine if its valid or invalid
        for term in fields:
            stripped_term = term.lstrip('-')
            # add back the '-' add the end if necessary
            reverse_sort_term = '' if len(stripped_term) is len(term) else '-'
            ordering = self.ordering_for(stripped_term, view)

            if ordering:
                valid_orderings.append(reverse_sort_term + ordering)
            else:
                invalid_orderings.append(term)

        return valid_orderings, invalid_orderings
Remove invalid fields from an ordering.

        Overwrites the DRF default remove_invalid_fields method to return
        both the valid orderings and any invalid orderings.