Could not persist aggregate because it seems to be changed by another process after it was retrieved in the current process. Current in-memory version is 1

[JustSteveKing]

My first time using v7 of the package, and had some issues with aggregates last night.

Could not persist aggregate PostAggregate (uuid: 19dad81e-b6ab-4012-a04a-401e1d35747d) because it seems to be changed by another process after it was retrieved in the current process. Current in-memory version is 1

Using Laravel 9.2.0
PHP 8.1

Aggregate:

class PostAggregate extends AggregateRoot
{
    protected static bool $allowConcurrency = false;

    public function createPost(DataObjectContract $object): self
    {
        $this->recordThat(
            domainEvent: new PostWasCreated(
                object: $object,
            ),
        );

        return $this;
    }

    public function getStoredEventRepository(): StoredEventRepository
    {
        return app(PostStoredEventsRepository::class);
    }
}

Event:

class PostWasCreated extends ShouldBeStored
{
    public function __construct(
        public readonly DataObjectContract $object,
    ) {}
}

Service Provider:

class EventSourcingServiceProvider extends ServiceProvider
{
    /**
     * @return void
     */
    public function register(): void
    {
        Projectionist::addProjector(
            projector: PostHandler::class,
        );

        Projectionist::addReactor(
            EmailModerators::class,
        );
    }
}

Projector:

class PostHandler extends Projector
{
    public function onPostWasCreated(PostWasCreated $event): void
    {
        /**
         * @var CreatePostContract
         */
        $action = resolve(CreatePostContract::class);

        $action->handle($event->object);
    }
}

The event is persisted in the database during testing with no errors, but when I interact with my code from the web UI - I get this issue. The aggregate is being triggered by a Livewire component that uses a service class to trigger the aggregate:

Livewire Component:

class CreateForm extends Component implements HasForms
{
    use InteractsWithForms;

    public bool $moderation = false;
    public null|string $title = null;
    public null|string $description = null;
    public null|string $content = null;
    public null|int $category = null;

    public function mount(): void
    {
        $this->form->fill();
    }

    public function submit(
        PostFactoryContract $factory,
        PostAggregateServiceContract $service,
    ) {
        $service->createPost(
            $factory->make(
                attributes: array_merge(
                    $this->form->getState(),
                    ['user_id' => auth()->id()],
                )
            )
        );

        return redirect()->route('dashboard');
    }

    protected function getFormSchema(): array
    {
        return [
            Grid::make(4)->schema([
                TextInput::make('title')->label('Post Title')->columnSpan(2)->required(),
                Select::make('category')->label('Post Category')->options(Category::get()->pluck('title', 'id'))->columnSpan(2)->required(),
                TextInput::make('description')->label('Post Description')->columnSpan(4)->required()->maxLength(120),
                MarkdownEditor::make('content')->label('Post Content')->columnSpan(4)->required(),
                    Toggle::make('moderation')->label('Submit for moderation')->columnSpan(4),
                ]),
        ];
    }

    public function render(): View
    {
        return view('livewire.posts.create-form');
    }
}

Service class:

class PostAggregateService implements PostAggregateServiceContract
{
    public function createPost(DataObjectContract $object): void
    {
        PostAggregate::retrieve(
            uuid: Str::uuid()->toString(),
        )->createPost(
            object: $object,
        )->persist();
    }
}

As you can see the service class tries to persist the aggregate, and this is where it fails. In my test code all I am doing is making sure that the event is stored:

it('triggers the aggregate root to store the event that a post was created', function () {
    $category = Category::factory()->create();
    auth()->loginUsingId(User::factory()->create()->id);

    expect(PostStoredEvent::query()->count())->toEqual(0);

    Livewire::test(CreateForm::class)
        ->set([
              'title' => 'pest php',
              'category' => $category->id,
              'description' => 'pest PHP is awesome, prove me wrong',
              'content' => 'Here be content, pirates and dragons',
          ])->call('submit')->assertHasNoErrors();

    expect(
        PostStoredEvent::query()->count()
    )->toEqual(1);
})->group('publishing');

[JustSteveKing]

Repo, if required: https://github.com/JustSteveKing/phponline.dev-new

[brendt]

Here's a whole discussion on concurrency: #214

There are two ways to solve your problem: use the command bus with the retry middleware (mentioned in that discussion), or manually refresh the ARs on places where these errors arise.

PS: please reopen this issue if the linked discussion doesn't solve the problem!

[JustSteveKing]

@brendt is this part in the v7 documentation at all? It sounds like it would solve the issue - but wouldn't mind reading your recommended approach 😄

[brendt]

I don't think it is… I added it as a kind of experimental feature, but maybe it's time to add it to the docs now.

Have you tried it out?

[JustSteveKing]

Not yet @brendt - if it is in the laravel event sourcing couese I could probably figure it out though

[anabeto93]

@JustSteveKing I'm wondering if you've been able to follow the discussion on #214 and resolved it. I haven't been able to follow through and implement the suggestions but we have worked out a way to make concurrent persists work for us in the mean time. Solution seems hacky and thus haven't bothered to create a PR to this package to have it added.

Found ourselves in a situation where you need the aggregate to persist no matter what. When dealing with transactions (payments), after processing all validation rules and ensuring this is a valid request that needs to be processed by an external microservice, it is bad to throw an error such as CouldNotPersistAggregate. It is not really the fault of the merchant/requestor making the request to the gateway that another process has already persisted the aggregate to a higher version.

Find below the link to a sample repository created, (on a separate branch), to enable concurrent persists. I am really hoping it helps someone and or someone improves upon it in a way that would also help us very much.

https://github.com/anabeto93/spatie-es-auto-discovery/pull/new/feature/allow-concurrent-persists

Helper function here is allowConcurrentPersists() and the tests in AllowsConcurrentPersistsTest might help explain the challenge.

When stress testing the current implementation of the gateway with event-sourcing using locustio, the majority of the errors that occur apart from http 429 mostly has to do with CouldNotPersistAggregate. Still playing around with $tries value to settle between a higher value (slower response times) or lower value (faster response times but with more CouldNotPersistAggregate errors).

[JustSteveKing]

Hey @anabeto93 I haven't tried this recently if I am honest, however I am about to start another event sourcing project soon - so will be able to see where this is in terms of ability to achieve.

I had issues following the discussion if I am honest, as the docs did not have anything about actually using the command bus. I will dig into this and see what I can figure out