Re: Any way to use JPA and JDO together easily?
Perhaps you would be better off looking at the DataNucleus (and JDO) documentation.
The JDO spec mandates being able to use JPA metadata (XML / annotations) with JDO persistence, and DataNucleus (JPA) also allows use of JDO metadata (XML / annotations) with JPA persistence.
DataNucleus seemingly allows use of JPQL with the JDO API (without the need to create any EntityManagerFactory), though not sure what query needs JPQL for that JDOQL can't express.
A query language like JPQL is in core code and hence available to both APIs.
Kodo doesn't seem to be as flexible as that ;-)