JPA : Datastore Replication

Many applications make use of multiple datastores. It is a common requirement to be able to replicate parts of one datastore in another datastore. Obviously, depending on the datastore, you could make use of the datastores own capabilities for replication. DataNucleus provides its own extension to JPA to allow replication from one datastore to another. This extension doesn't restrict you to using 2 datastores of the same type. You could replicate from RDBMS to XML for example, or from MySQL to HSQLDB.

You need to make sure you have the persistence property datanucleus.attachSameDatastore set to false if using replication

Note that the case of replication between two RDBMS of the same type is usually way more efficiently replicated using the capabilities of the datastore itself

The following sample code will replicate all objects of type Product and Employee from EMF1 to EMF2. These EMFs are created in the normal way so, as mentioned above, EMF1 could be for a MySQL datastore, and EMF2 for XML. By default this will replicate the complete object graphs reachable from these specified types.

import org.datanucleus.api.jpa.JPAReplicationManager;


JPAReplicationManager replicator = new JPAReplicationManager(emf1, emf2);
replicator.replicate(new Class[]{Product.class, Employee.class});