Aggregate polymorphism and AggregateMembers

Axon Framework
1

Hi, I have a problem with the usage of @Aggregate members in combination with aggregate polymorphism. I think a simple code example illustrates this best :

The ‘parent’ aggregate

@Aggregate
@NoArgsConstructor
public class School {
    @AggregateIdentifier
    private String schoolId;

    @CommandHandler
    public School(CreateSchoolCommand command) {
        apply(new SchoolCreatedEvent(command.schoolId()));
    }

    @EventSourcingHandler
    public void handle(SchoolCreatedEvent event) {
        this.schoolId = event.schoolId();
    }
}

The subclass aggregate with aggregate member:

@Aggregate
@RequiredArgsConstructor
public class PrimarySchool extends School {
    @AggregateMember
    final Map<String, Group> groups = new HashMap<>();

    @CommandHandler
    public void handle(CreatePrimarySchoolGroupCommand command) {
        apply(new PrimarySchoolGroupCreatedEvent(command.schoolId(), command.groupId()));
    }

    @EventSourcingHandler
    public void handle(PrimarySchoolGroupCreatedEvent event) {
        this.groups.putIfAbsent(event.schoolId(), new Group(event.groupId()));
    }
}

And the definition of the Group entity :

@AllArgsConstructor
public class Group {
    @EntityId
    private String schoolId;
}

The issue I have is that this only works if I put the groups aggregate member in the parent (School) aggregate, if it is defined in the PrimarySchool aggregate, then I get the following error :

Exception in thread "main" org.axonframework.commandhandling.CommandExecutionException: Unable to access field for getting.
Caused by: AxonServerRemoteCommandHandlingException{message=An exception was thrown by the remote message handling component: Unable to access field for getting.
Caused by Can not set final java.util.Map field nl.ronob.demo.aggregate.polymorphism.domain.PrimarySchool.groups to nl.ronob.demo.aggregate.polymorphism.domain.School, errorCode='AXONIQ-4002', server='18193@pop-os'}

However, I would like the aggregate member definition in the PrimarySchool aggregate, but I cannot get my head around what I’m doing something wrong ?
(Btw, if needed I can provide a sample spring boot app to replicate this behavior)

2

Have you tried removing the final keyword on the groups map?

3

yes I did, I don’t think the actual problem is an accessibility (related to reflection) issue. To me, it looks like somehow the ‘groups’ field is set in the parent class (School) instead of PrimarySchool where it is actually defined as aggregateMember :

Caused by Can not set final java.util.Map field nl.ronob.demo.aggregate.polymorphism.domain.PrimarySchool.groups to nl.ronob.demo.aggregate.polymorphism.domain.School, errorCode='AXONIQ-4002'