private function getFilterOperator($filter)
    {
        $operator = str_replace('notlike', 'not like', $filter);
        $operator = str_replace('gt', '>', $operator);
        $operator = str_replace('ge', '>=', $operator);
        $operator = str_replace('lt', '<', $operator);
        $operator = str_replace('le', '<=', $operator);
        $operator = str_replace('eq', '=', $operator);
        $operator = str_replace('ne', '!=', $operator);

        return $operator;
    }