ObjectDB manages automatic entity versioning (for optimistic lock purposes). Every entity object modification is reflected by a new version number. Naturally, previous values in the entity object that are overridden by new values are discarded.
Some applications may benefit from the ability to go back in time and view old versions (and old values) of entity objects. Future versions of ObjectDB should support archiving old versions of specific entity classes, similarly to the functionality of tools such as Hibernate Envers.
ObjectDB - Fast Object Database for Java (JPA/JDO)