I guess you have to check your database for that kind of functionality. Hibernate doesn't generally generate values for you automatically. The only exception are some of the ID generators.
It might be possible to implement some kind of auto-generation with a custom UserType, but not if you depend on the auto-increment value that is generated by the database.
On the other hand, Hibernate has support for calculated properties. Eg. properties that are not stored in the database, but are calculated on the fly (using SQL) each time the data is read from the database. See <property formula=...> at
http://www.hibernate.org/hib_docs/v3/re ... n-property