Category "datanucleus"

App Engine Datanucleus JPA throwing javax.persistence.PersistenceException on Collection properties of Entities

The error occurs at runtime after the enhancement has been done successfully. I thought it had got to do with entity relationships but further probe showed that

Nested ID class required to be named like relationship, even though not being a derived identifier?

There's chapter 10 in the book "Pro JPA 2 in Java EE 8", section called "Multiple Mapped Attributes", there the well-known department-project example using @IdC