Friday, February 26, 2016

Inheritance with Aggregate Roots in ProophEvent-Store

If you want to make inheritance work with aggregate roots using a common repository for all subtypes, this can be achieved very easily. You need the latest ProophEvent-Store v6.1 to do this.

An example


Consider the following use case:

<?php
abstract class User extends \Prooph\EventSourcing\AggregateRoot
{
    protected $name;

    protected $email;

    public function name()
    {
        return $this->name;
    }

    public function email()
    {
        return $this->email;
    }

    protected function whenUserWasRegisterd(UserWasRegisterd $event)
    {
        $this->name = $event->name();
        $this->email = $event->email();
    }
}

class Admin extends User
{
    public static function register($name, $email)
    {
        $self = new self();
        $self->recordThat(UserWasRegisterd::withData('admin', $name, $email);

        return $self;
    }
}

class Member extends User
{
    public static function register($name, $email)
    {
        $self = new self();
        $self->recordThat(UserWasRegisterd::withData('member', $name, $email);

        return $self;
    }
}
So in order to make this work, you need 3 small changes in your application.

Step 1: Create a UserAggregateTranslator


<?php
final class UserAggregateTranslator extends \Prooph\EventSourcing\EventStoreIntegration\AggregateTranslator
{
    /**
     * @param \Prooph\EventStore\Aggregate\AggregateType $aggregateType
     * @param \Iterator $historyEvents
     * @return object reconstructed AggregateRoot
     */
    public function reconstituteAggregateFromHistory(
        \Prooph\EventStore\Aggregate\AggregateType $aggregateType, 
        \Iterator $historyEvents
    ) {
        $aggregateRootDecorator = $this->getAggregateRootDecorator();

        $firstEvent = $historyEvents->current();
        $type = $firstEvent->type();

        if ($type === 'admin') {
            return $aggregateRootDecorator->fromHistory(Admin::class, $historyEvents);
        } elseif ($type === 'member') {
            return $aggregateRootDecorator->fromHistory(Member::class, $historyEvents);
        }
    }
}

Step 2: Change the assertion method in the EventStoreUserCollection


<?php
final class EventStoreUserCollection extends 
    \Prooph\EventStore\Aggregate\AggregateRepository
{
    public function add(User $user)
    {
        $this->addAggregateRoot($user);
    }
    public function get(UserId $userId)
    {
        return $this->getAggregateRoot($userId->toString());
    }
    protected function assertAggregateType($eventSourcedAggregateRoot)
    {
        \Assert\Assertion::isInstanceOf($eventSourcedAggregateRoot, User::class);
    }
}

Step 3: Make use of your custom AggregateTranslator


<?php
final class EventStoreUserCollectionFactory
{
    public function __invoke(ContainerInterface $container)
    {
        return new EventStoreUserCollection(
            $container->get(EventStore::class),
            AggregateType::fromAggregateRootClass(User::class),
            new UserAggregateTranslator()
        );
    }
}

If you use the provided container factory (\Prooph\EventStore\Container\Aggregate\AbstractAggregateRepositoryFactory) then you can also just change the aggregate_translator key in your config to point to the new UserAggregateTranslator and register the UserAggregateTranslator in your container.

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