as I know that some of you are already in production with a snapshot version of Axon 2.0, here is a warning: I am deploying a new snapshot version that contains some incompatible changes.
From now on, event sourced aggregates consisting of more than entity need to explicitly identify their"child entities". If you extend AbstractEventSourcedAggregateRoot or EventSourcedEntity directly, you will need to implement the getChildEntities() method yourself. If instead you subclass AbstractAnnotatedAggregateRoot or AbstractAnnotatedEntity, you can place the @EventSourcedMember annotated on the field(s) that contain these child entities.
What you get back for it is a performance improvement. There was quite a penalty to pay for the field scanning approach that was previously implemented. Scanning fields for annotations is a one-time procedure.
I will update the reference guide to reflect these changes soon.