protected function basicSerialize()
    {
        return [
            'type' => $this->getEventType(),
            'transaction' => $this->transactionId,
            'primary_key' => $this->id,
            'source' => $this->source,
            'parent_source' => $this->parentSource,
            '@timestamp' => $this->timestamp,
            'meta' => $this->meta
        ];
    }