Major Description
It's a pitty that @PersistentCollection(elementEmbedded = true) only works to to "depth 1", that is you can apparently not have an @Entity class A
{ @PersistentCollection(elementEmbedded=true) private Set<B> bs = new HashSet<B>(); ... }with @Entity class B again a
{ @PersistentCollection(elementEmbedded=true) private Set<C> bs = new HashSet<C>(); ... }.
On OpenJPA 1.1, this leads to the error: "org.apache.openjpa.util.MetaDataException: "X.y<element:class Y>" is mapped as embedded, but embedded field "..." is not embeddable. Embedded element/key/value types are limited to simple fields and direct relations to other persistent types."
The expected outcome would to have a schema with an SQL table A, an A_B (that works already!), and an A_B_C table (that doesn't work).
JPA 2.0 JSR 317 <http://jcp.org/en/jsr/detail?id=317> says "... support for collections of embedded objects, multiple levels of embedded objects ..." so may this will be supported 'soon-ish' (that one liner may not refer to this exact use case)?
PS: This limitation has unfortunately turned into a show stopper for our use of OpenJPA, and made us look at another ORM which seems to support this kind of mapping.