def _construct_qs_filter(self, field_name):
        """
        Using a field name optionnaly prefixed by `^`, `=`, `@`, return a
        case-insensitive filter condition name usable as a queryset `filter()`
        keyword argument.
        """
        if field_name.startswith('^'):
            return "%s__istartswith" % field_name[1:]
        elif field_name.startswith('='):
            return "%s__iexact" % field_name[1:]
        elif field_name.startswith('@'):
            return "%s__search" % field_name[1:]
        else:
            return "%s__icontains" % field_name
Using a field name optionnaly prefixed by `^`, `=`, `@`, return a
        case-insensitive filter condition name usable as a queryset `filter()`
        keyword argument.