Using your own event serializer

Events will be serialized by the Spatie\EventSourcing\EventSerializers\JsonEventSerializer. Like the name implies, this class can serialize an event to json so it can be easily stored in a json column in the database.

You can specify your own serializer by creating a class that implements Spatie\EventSourcing\EventSerializers\EventSerializer and specifying the class in the event_serializer key of the event-sourcing.php config file.

This is the content of the EventSerializer interface:

namespace Spatie\EventSourcing\EventSerializers;

use Spatie\EventSourcing\ShouldBeStored;

interface EventSerializer
{
    public function serialize(ShouldBeStored $event): string;

    public function deserialize(string $eventClass, string $json, string $metadata): ShouldBeStored;
}

##Upgrading Events

If an event payload has changed overtime, old events can be "upgraded" to the new payload on the fly in the event serializer.

Using our larabank example, let's imagine that we've gone international and our new accepting international payments. Our MoneyAdded events will need to have an additional field for the currency.

class UpgradeSerializer extends JsonEventSerializer
{
    public function deserialize(string $eventClass, string $json, string $metadata = null): ShouldBeStored
    {
        $event = parent::deserialize($eventClass, $json, $metadata);

        // all currency was USD before we started accepting other currencies
        if (empty($event->currency)) {
            $event->currency = 'USD';
        }

        return $event;
    }
}

## Want to know more?

Our course, [Event Sourcing in Laravel](https://event-sourcing-laravel.com/) covers this topic in depth:

- 18. Event Versioning