Message Decorator

There are usecases 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.

RecordedOnDecorator

Each message needs a RecordedOn time. The RecordedOnDecorator is needed so that this is added to the message. This decorator needs a clock implementation.

use Patchlevel\EventSourcing\Clock\SystemClock;
use Patchlevel\EventSourcing\EventBus\Decorator\RecordedOnDecorator;

$clock = new SystemClock();
$decorator = new RecordedOnDecorator($clock);

Warning

A RecordedOn time must always be created. Either this decorator must always be added or an appropriate replacement must be provided.

SplitStreamDecorator

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

use Patchlevel\EventSourcing\EventBus\Decorator\SplitStreamDecorator;
use Patchlevel\EventSourcing\Metadata\Event\AttributeEventMetadataFactory;

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

ChainMessageDecorator

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

use Patchlevel\EventSourcing\EventBus\Decorator\ChainMessageDecorator;

$decorator = new ChainMessageDecorator([
    $decorator1,
    $decorator2,
]);

Use decorator

To use the message decorator, you have to pass it to the DefaultRepositoryManager.

use Patchlevel\EventSourcing\EventBus\Decorator\ChainMessageDecorator;
use Patchlevel\EventSourcing\EventBus\Decorator\RecordedOnDecorator;
use Patchlevel\EventSourcing\Repository\DefaultRepositoryManager;

$decorator = new ChainMessageDecorator([
    new RecordedOnDecorator($clock),
    new SplitStreamDecorator($eventMetadataFactory)  
]);

$repositoryManager = new DefaultRepositoryManager(
    $aggregateRootRegistry,
    $store,
    $eventBus,
    null,
    $decorator
);

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

Warning

We also use the decorator to fill in the RecordedOn time. If you want to add your own decorator or the SplitStreamDecorator, then you need to make sure to add the RecordedOnDecorator as well.

Note

You can find out more about repository here.

Create own decorator

You can also use this feature to add your own metadata to your events. For this the have an extra methods on Message to add data withCustomHeader and to read this data later on customHeader.

use Patchlevel\EventSourcing\EventBus\Message;

final class OnSystemRecordedDecorator implements MessageDecorator
{
    public function __invoke(Message $message): Message
    {
        return $message->withCustomHeader('system', 'accounting_system');
    }
} 

Note

The Message is immutable, for more information look up here.

Tip

You can also set multiple headers with withCustomHeaders which expects an hashmap.