AF5: @InjectEntity not working on static handler (Migration of CREATE_IF_MISSING)

Axon Framework
1

Hi
the AF5 migration guide says that you can use @InjectEntity in the static entity creator method:

CreationPolicy.CREATE_IF_MISSING

If you need “only create if missing” logic, you can implement it within the static handler by checking for the existence of an optional state parameter.

@CommandHandler
public static void handle(IssueGiftCard cmd,
                          EventAppender eventAppender,
                          @InjectEntity @Nullable GiftCard giftCard) {
    if (giftCard != null) {
        throw new IllegalStateException("GiftCard already exists");
    }
    eventAppender.append(new GiftCardIssued(cmd.cardId(), cmd.amount()));
}

I don’t know if this is “just” a bug in the migration docs or if this is a bug in Axon.

I get an EntityAlreadyExistsForCreationalCommandHandlerException before the static handle method is called again with the entity injected.

Simple example reproducing this using the CourseCreation example:

@Validated
@EventSourced(tagKey = FacultyTags.COURSE_ID, idType = CourseId.class)
@Slf4j
public class CourseCreation {

  private boolean created = false;
  private CourseId id;
  private int capacity;

  @CommandHandler
  public static void create(
      @Valid CreateCourse command,
      EventAppender appender,
      @InjectEntity @Nullable CourseCreation entity) {
    if (entity == null) {
      appender.append(
          new CourseCreated(
              command.courseId(),
              command.name(),
              command.capacity()
          )
      );
    } else {
      // do something different
    }
  }

  @EntityCreator
  public CourseCreation(CourseCreated courseCreated) {
    this.id = courseCreated.courseId();
    this.created = true;
    this.capacity = courseCreated.capacity();
  }
}

Following test fails:

    fixture.given()
        .events(new CourseCreated(courseId, "Introduction to Axon Framework", 30))
        .when()
        .command(new CreateCourse(courseId, "Introduction to Axon Framework", 30))
        .then()
        .success()
        ;

with

org.axonframework.modelling.entity.EntityAlreadyExistsForCreationalCommandHandlerException: Creational command handler for command [org.axonframework.examples.university.write.createcourse.CreateCourse#0.0.1] encountered an already existing entity: [org.axonframework.examples.university.write.createcourse.CourseCreation@6b68cb27]
	at org.axonframework.modelling.entity.ConcreteEntityMetamodel.handleInstance(ConcreteEntityMetamodel.java:147)
	at org.axonframework.modelling.entity.annotation.AnnotatedEntityMetamodel.handleInstance(AnnotatedEntityMetamodel.java:500)
	at org.axonframework.modelling.entity.EntityCommandHandlingComponent.lambda$handle$1(EntityCommandHandlingComponent.java:107)
	at java.base/java.util.concurrent.CompletableFuture.uniApplyNow(CompletableFuture.java:684)
	at java.base/java.util.concurrent.CompletableFuture.uniApplyStage(CompletableFuture.java:662)
	at java.base/java.util.concurrent.CompletableFuture.thenApply(CompletableFuture.java:2200)
	at org.axonframework.modelling.entity.EntityCommandHandlingComponent.handle(EntityCommandHandlingComponent.java:103)

Klaus

2

Not a 100% sure, as I am mostly triggering on the title, but I think you’re hitting `EntityNotFoundException` behavior around `@EntityCreator` usage for Entity-centric and Stateful-Handler-based instance command handling by smcvb · Pull Request #4609 · AxonIQ/AxonFramework · GitHub here, @klauss42. If you move that command handler outside of the entity/aggregate, I’d anticipate things to work as desired.

3

Steven, you are right. If the static command handler is outside of the aggregate class, the injected entity is set. Kind of confusing…

Klaus

4

Yes, totally agreed it’s confusing! As there’s a PR, you can be ascertained the issue will be tackled accordingly in due time. Sorry for the inconvenience for the time being!