How to transfer entities from one database to another

pkorzeniewicz · **Joined:** Tue Jul 22, 2008 8:56 am **Posts:** 3

Hi,

I have a database DB1 with a table T1. The entities stored in T1 have auto-generated IDs:

Code:

@Entity
public class MyEntity
{
  @Id
  @GeneratedValue
  private int id;
}

Now I need to transfer some entities to another database DB2. Both DB1 and DB2 are accessed via Hibernate. A mapping for MyEntity is configured for both databases. If I try the following:

Code:

// session1 is an open session to DB1
// session2 is an open session to DB2

MyEntity entity = (MyEntity) session1.load(...);
session1.evict(entity);
session2.save(entity);

I obviously get an exception because session2 tries to alter the auto-generated ID.

If I remove the @GeneratedValue annotation from the MyEntity class definition it works but then I would have to generate the IDs myself (before saving the entities to DB1) so that would be very ugly and error-prone.

I also tried to write a sublcass to MyEntity (let's say MyEntity2) and to override the id property like the following (i.e. trying to make the id not auto-generated):

Code:

@Entity
public class MyEntity
{
  @Id
  @GeneratedValue
  protected int id;
  ...
}

@Entity
public class MyEntity2 extends MyEntity
{
  @Id
  protected int id;
}

but I get an exception. It seems that you cannot ovverride the annotation

Can anyone suggest a solution?

jbosseur · **Posted:** Fri Jul 25, 2008 2:25 pm

The id´s for the entities need to be the same i presume?

pkorzeniewicz · **Joined:** Tue Jul 22, 2008 8:56 am **Posts:** 3

jbosseur wrote:

The id´s for the entities need to be the same i presume?

Yes this is exactly the point. As far as I can see there is no way to store entities in both databases with identical IDs.

I actually "solved" the problem by defining a synchronization strategy that works evend if identical entities have different IDs. But it works only in the special context of my application.