Bolt\Storage\Repository\FieldValueRepository::getExistingFields PHP Method

    public function getExistingFields($id, $contenttype, $field)
    {
        $query = $this->queryExistingFields($id, $contenttype, $field);
        $results = $query->execute()->fetchAll();
        $fields = [];
        if (!$results) {
            return $fields;
        }
        foreach ($results as $result) {
            $fields[$result['grouping']][] = $result['id'];
        }
        return $fields;
    }