private function getMessage($revision)
    {
        switch ($revision->key) {
            case 'created_at':
                return $this->getResponsibleInfo($revision) . ' created user '
                    . $this->getAffectedResourceName($revision) . ' (' . $revision->revisionable_id . ')';
            case 'deleted_at':
                return $this->getResponsibleInfo($revision) . ' deleted user '
                    . $this->getAffectedResourceName($revision) . ' (' . $revision->revisionable_id . ')';
            default:
                return $this->getResponsibleInfo($revision) . ' changed user '
                    . $this->getAffectedResourceName($revision) . ' (' . $revision->revisionable_id . ')'
                    . ' field ' .  $revision->fieldName() . ' from ' .$revision->oldValue() . ' to ' .
                    $revision->newValue();
        }
    }