broadway / snapshotting

Proof-of-concept component providing snapshotting functionality to Broadway

Broadway

Broadway is a project providing infrastructure and testing helpers for creating CQRS and event sourced applications. Broadway tries hard to not get in your way. The project contains several loosely coupled components that can be used together to provide a full CQRS\ES experience.

About

Read the blog post about this repository at:

• http://labs.qandidate.com/blog/2014/08/26/broadway-our-cqrs-es-framework-open-sourced/

Installation

$ composer require broadway/broadway

Documentation

You can find detailed documentation of the Broadway bundle on broadway.github.io/broadway.

Feel free to join #qandidate on freenode with questions and remarks!

Acknowledgements

The broadway project is heavily inspired by other open source project such as AggregateSource, Axon Framework and Ncqrs.

We also like to thank Benjamin, Marijn and Mathias for the conversations we had along the way that helped us shape the broadway project. In particular Marijn for giving us access to his in-house developed CQRS framework.

License

MIT, see LICENSE.

snapshotting's Issues

implement snapshotting

continued from

• broadway/broadway#111
• broadway/broadway#147

SnapshottingEventSourcingRepository missing return type

Class implements the Broadway\Repository\Repository interface:

public function save(AggregateRoot $aggregate): void;

but the implementation's method signature does not include the void return type.

support PHP 5.6

This repos requires PHP 7
Do we want to support PHP 5.6?

Snapshot does not register aggregate root for EventSourcedEntities

When an event is applied to an aggregate it is handled recursively, meanwhile registering the aggregate root for child entities.

class Broadway\EventSourcing\EventSourcedAggregateRoot {
....
  protected function handleRecursively($event)
  {
        $this->handle($event);

        foreach ($this->getChildEntities() as $entity) {
            $entity->registerAggregateRoot($this);
            $entity->handleRecursively($event);
        }
  }
...
}

Snapshot is just a serialized object. So there is no handling of a snapshot that registers aggregate root for child entities.

If there is at least one event after the snapshot, following method registers the aggregages for child entities;

class Broadway\EventSourcing\EventSourcedAggregateRoot {
....    
public function initializeState(DomainEventStream $stream)
  {
      foreach ($stream as $message) {
          ++$this->playhead;
          $this->handleRecursively($message->getPayload());
      }
  }
...
}

But if there are no events after snapshot, and you want to apply an event to your entities (which in turn would apply the event to the aggregate root, you will get an error;
Call to a member function apply() on null
(see an implementation https://github.com/broadway/broadway/blob/master/src/Broadway/EventSourcing/SimpleEventSourcedEntity.php#L53)

One easy solution is to change EventSourcedAggregateRoot::initializeState method to register aggregate roots for child entities even if there's no event coming after the snapshot.

class Broadway\EventSourcing\EventSourcedAggregateRoot {
....
    public function initializeState(DomainEventStream $stream)
    {

        // added block
        foreach ($this->getChildEntities() as $entity) {
            $entity->registerAggregateRoot($this);
        }

        foreach ($stream as $message) {
            ++$this->playhead;
            $this->handleRecursively($message->getPayload());
        }
    }
...
}

Currently I can override initializeState in my aggregate root. But it would be good if this was done in abstract class
EventSourcedAggregateRoot.

Hope it is clear. Any opinions? Is there something I am missing?
Thanks in advance