public function columns(array $fields, QueryParameters $queryParameters = null) {
        $select = '';
        foreach($fields as $field) {
            $select .= 'o.' . $field;
            if($field !== last($fields)) {
                $select .= ', ';
            }
        }
        $qb = $this->entities->createQueryBuilder()
            ->select($select)
            ->from($this->entityName, 'o');

        return $this->getQuery($qb, $queryParameters)->getResult();
    }