Java Data Objects and automatic schema migration

Does there exist a tool or facility in jdo which will allow you to automatically migrate a schema based from the .jdo files? For example suppose I have a class called Foo with integer fields bar and baz and a metadata file that describes that and a table in the database that mirrors the java class. Now, let’s say that I add a field to Foo called bim and make the appropriate additions to the metadata. Is there a tool that I can use to generate the DDL which would alter the Foo table in the database to match Foo v2.0? What about the DDL necessary to roll back?

Thanks for your help,
Rob

Surely, there must be someone who knows something about JDO. What about Hibernate? Is there a tool that does what I described for Hibernate?

Thanks,
Rob