I don't get it: CouldNotPersistAggregate with just one worker on the event-sourcing queue

[ahoiroman]

Hi there,

I don't get it. I recently saw a error popping out that told me this:

Spatie\EventSourcing\AggregateRoots\Exceptions\CouldNotPersistAggregate
Could not persist aggregate ItemAggregateRoot (uuid: 01971d73-5e2f-7386-97ae-bd2ee945da18) because it seems to be changed by another process after it was retrieved in the current process. Current in-memory version is 11

Ok. So I assume that my aggregate has been changed in the meantime. Okay. But I don't get it, because:

• I am using a dedicated single-process queue for event sourcing
• I am using the command bus
• My reactor that triggers the event that leads to this problem, is queued

public function onCheckoutFailed(CheckoutFailed $event): void
{
    $cart = Cart::findByAggregateUuid($event->aggregateRootUuid());

    app(RestoreStock::class)(cart: $cart);
}

That action class does this:

final readonly class RestoreStock extends EventSourcedAction
{
    public function __invoke(Cart $cart): void
    {
        $this->bus->dispatch(
            new RestoreStockCommand(
                aggregateUuid: $cart->aggregate_uuid
            )
        );
    }
}

So I do not get how I'd have to refresh the aggregate root. How would I do that? And why is it possible that two processes are messing around with that aggregate at the same time?

I'd really love to hear your opinions.