Message Decorator

There are use-cases where you want to add some extra context to your events like metadata which is not directly relevant for your domain. With MessageDecorator we are providing a solution to add this metadata to your events. The metadata will also be persisted in the database and can be retrieved later on.

Built-in decorator

We offer a few decorators that you can use.

SplitStreamDecorator

In order to use the split stream feature, the SplitStreamDecorator must be added.

use Patchlevel\EventSourcing\Metadata\Event\AttributeEventMetadataFactory;
use Patchlevel\EventSourcing\Repository\MessageDecorator\SplitStreamDecorator;

$eventMetadataFactory = new AttributeEventMetadataFactory();
$decorator = new SplitStreamDecorator($eventMetadataFactory);

ChainMessageDecorator

To use multiple decorators at the same time, you can use the ChainMessageDecorator.

use Patchlevel\EventSourcing\Repository\MessageDecorator\ChainMessageDecorator;
use Patchlevel\EventSourcing\Repository\MessageDecorator\MessageDecorator;

/**
 * @var MessageDecorator $decorator1
 * @var MessageDecorator $decorator2
 */
$decorator = new ChainMessageDecorator([
    $decorator1,
    $decorator2,
]);

Use decorator

To use the message decorator, you have to pass it to the DefaultRepositoryManager, which will then pass it to all Repositories.

use Patchlevel\EventSourcing\Metadata\AggregateRoot\AggregateRootRegistry;
use Patchlevel\EventSourcing\Metadata\Event\EventMetadataFactory;
use Patchlevel\EventSourcing\Repository\DefaultRepositoryManager;
use Patchlevel\EventSourcing\Repository\MessageDecorator\ChainMessageDecorator;
use Patchlevel\EventSourcing\Repository\MessageDecorator\SplitStreamDecorator;
use Patchlevel\EventSourcing\Store\Store;

/** @var EventMetadataFactory $eventMetadataFactory */
$decorator = new ChainMessageDecorator([new SplitStreamDecorator($eventMetadataFactory)]);

/**
 * @var AggregateRootRegistry $aggregateRootRegistry
 * @var Store $store
 */
$repositoryManager = new DefaultRepositoryManager(
    $aggregateRootRegistry,
    $store,
    null,
    null,
    $decorator,
);

$repository = $repositoryManager->get(Profile::class);

You can find out more about the repository.

Create own decorator

You can also use this feature to add your own metadata to your events. For this, the Message has extra methods: withHeader to add data and header to read this data later on.

use Patchlevel\EventSourcing\Attribute\Header;
use Patchlevel\EventSourcing\Message\Message;
use Patchlevel\EventSourcing\Repository\MessageDecorator\MessageDecorator;

#[Header('system')]
final class SystemHeader
{
    public function __construct(
        public string $system,
    ) {
    }
}

final class OnSystemRecordedDecorator implements MessageDecorator
{
    public function __invoke(Message $message): Message
    {
        return $message->withHeader(new SystemHeader('system'));
    }
}

The message is immutable, more information can be found in the message documentation.

You can also set multiple headers with withHeaders which expects a list of headers.