Envers 1.2.1 GA

Envers project aims to enable easy versioning of persistent classes. All that you have to do is annotate your persistent class or some of its properties, that you want to version, with @Versioned. For each versioned entity, a table will be created, which will hold the history of changes made to the entity.
Similarly to Subversion, the library has a concept of revisions. Basically, one transaction commit is one revision (unless the transaction didnt modify any versioned entities).
As the revisions are global, having a revision number, you can query for various entities at that revision, retrieving a (partial) view of the database at that revision.
The library works with the latest Hibernate and Hibernate Entity Manager versions (see hibernate.org). For the versioning to work properly, the entities must have immutable unique identifiers (primary keys).
In the future, the Envers library will support versioning of arbitrary relationships. It will also include support for "revisioning groups", which will de-centralize the revisions table, if there are independend groups of entities versioned.
Another important space-saving feature will be the possibility to store only diffs between revisions, not whole properties (this of course applies only to strings).

Main features:
- versioning of basic properties (strings, integers, longs...)
- versioning of embedded components, which are composed of basic properties
- versioning of classes with simple, composite and embedded ids
- versioning of one-to-one uni- and bi-directional relations
- versioning of one-to-many bi-directional relations
- logging data for each revision using a "revision entity"
- querying historical data