protected function normalizeLogical($operator)
    {
        switch (strtolower($operator)) {
            case '&&':
            case 'and':
                return 'and';
            case '||':
            case 'or':
                return 'or';
            default:
                throw new QueryException(sprintf('Query does not supports logical operator "%s" in query "%s"', $operator, $this->model()->entity()));
        }
    }