Event sourced aggregate with multiple CreatedEvents in 3.0.3

Imported from Google Groups
1

Hi,
I have simple app with following create-related methods in the aggregate

`
@CommandHandler
public Counter(CounterCreateCommand command, MetaData metaData) {
super();
AggregateLifecycle.apply(new CounterCreatedEvent(command.getId()), metaData);
}

@EventSourcingHandler
public void on(CounterCreatedEvent e) {
this.id = e.getId();
this.counter = 0;
}
`

It looks like I am able to issue the CounterCreateCommand multiple times, resulting into the CounterCreatedEvent being written each time.

I thought the framework will prevent double-creation of aggregate. Or am I missing something obvious here?

2

Hi Tomáš,

What is the id set to in your CounterCreateCommand?
Can you publish two CounterCreateCommands with identical id’s, or is the ‘issuing of multiple commands’ you refer to creating a CounterCreateCommand with unique ids?
As far as I know, that should result in an exception when your CounterCreatedEvent is trying to be stored, because you’d try storing a second CounterCreatedEvent with an identical aggregate identifier and sequence number.

Hope this helps!

Cheers,

Steven

3

Well that’s exactly what I expected as well - some kind of error flow. And yes, I am using the same id, the configuration is like this:

`
public static void main(String[] args) throws Exception {
Configurer configurer = DefaultConfigurer
.defaultConfiguration()
.configureEmbeddedEventStore(c -> new InMemoryEventStorageEngine())
.configureAggregate(Counter.class);

Configuration configuration = configurer.buildConfiguration();
configuration.start();

String id = “my-static-id”;
configuration.commandGateway().sendAndWait(new CounterCreateCommand(id));
configuration.commandGateway().sendAndWait(new CounterCreateCommand(id));

configuration.eventStore().readEvents(id).asStream().forEach(System.out::println);
}
`

The console output:

DEBUG [main] (Counter.java:28) - +++ CounterCreateCommand received for my-static-id created 391359742 DEBUG [main] (Counter.java:36) - + counter my-static-id consuming create : 391359742 DEBUG [main] (Counter.java:28) - +++ CounterCreateCommand received for my-static-id created 485041780 DEBUG [main] (Counter.java:36) - + counter my-static-id consuming create : 485041780 org.axonframework.eventsourcing.GenericTrackedDomainEventMessage@20322d26 org.axonframework.eventsourcing.GenericTrackedDomainEventMessage@192b07fd

4

Hi Tomas,

it seems you’re using the InMemoryEventStorageEngine. That one (for some reason) doesn’t check for uniqueness. It just adds all published events to a list.
You’re better off using the JpaEventStorageEngine with an InMemory database if you want to be “production compatible”.

Cheers,

Allard

5

Thanks Allard. I am actually using the MongoEventStorageEngine

new MongoEventStorageEngine(new DefaultMongoTemplate(new MongoClient("10.128.75.101"), "axonframework", "domainevents", "snapshotevents"))

but with the same result. The Mongo is v3.4 just fresh install. Anyway atm I will move away from mongo in favour of couchbase. I can see that this is solved in AbstractEventStorageEngine by the datastore throwing an exception and being handled properly.

Cheers.

6

Hi Tomas,

are the indexes in place? There should be a unique index on the aggregateIdentifier and sequenceNumber properties. If there isn’t, you can create it by calling “ensureIndexes” on your MongoEventStorageEngine instance.

Cheers,

Allard

7

No, they weren’t created. When adding the index manually all worked as expected.