From what I have understand the JPA 2.1 support "An embeddable class may contain a relationship to an entity or collection of entities."
I have tried various mapping with no luck, they all throw a ConcurrentModificationException.
Test case attached to the jira
I added a replicating test case in hibernate-core:
Assuming we fix the ConcurrentModificationException so that, in InFlightMetadataCollectorImpl, instead of:
we do this:
The mapping will still fail with the following error message:
There is more to be changed to support such a mapping.