It is occasionally useful to be able to take a graph of persistent instances and make them persistent in a different datastore, without regenerating identifier values.
//retrieve a cat from one database Session session1 = factory1.openSession(); Transaction tx1 = session1.beginTransaction(); Cat cat = session1.get(Cat.class, catId); tx1.commit(); session1.close(); //reconcile with a second database Session session2 = factory2.openSession(); Transaction tx2 = session2.beginTransaction(); session2.replicate(cat, ReplicationMode.LATEST_VERSION); tx2.commit(); session2.close();
The ReplicationMode
determines how replicate()
will deal with conflicts with existing rows in the database.
ReplicationMode.IGNORE
- ignore the object when there is
an existing database row with the same identifier
ReplicationMode.OVERWRITE
- overwrite any existing database
row with the same identifier
ReplicationMode.EXCEPTION
- throw an exception if there is
an existing database row with the same identifier
ReplicationMode.LATEST_VERSION
- overwrite the row if its
version number is earlier than the version number of the object, or ignore
the object otherwise
Usecases for this feature include reconciling data entered into different database instances, upgrading system configuration information during product upgrades, rolling back changes made during non-ACID transactions and more.