Hello,

I am trying to use hibernate to migrate data between two databases. The approach I was thinking was basically to have a hbm.xml mapping file to map the source data to a POJO, within the context of a "source" database hibernate session, then use the same POJO to map to a different hbm.xml file associated with a "destination" database hibernate session.

Based on documentation and reading through some forum posts, it sounds like I would want to do a procedure like:

1. start new "source" hibernate session
2. load the rows for a database table into a collection (my dataset is small)
3. close the hibernate session, so that the objects become "detached"
4. start a new "destination" hibernate session, start transaction
5. save the items from the collection ("session.save(eachItem)"). (I know there are facilities for batch saving items, but i want to get it working first, and then worry about optimizing.)
6. commit transaction

One of the objects has a <list> of children. On both the "source" and "destination" hbm.xml, it is configured as such (names generalized for simplicity):


(There are other parts of the hbm.xml files where other parts of the mapping differ, which is why I am not using the same file on both sides.)

What is happening is that the <list> of items is not getting saved to the destination database.

Could someone be so kind as to point out what I am doing wrong? Perhaps my approach is not optimal?

Cheers,

Alex

I found the cause, per this sentence in the Hibernate documentation:


I get why that is the case under normal, single session use cases. I suppose I was under the impression that the proxy classes would be removed once the session was closed, or if one evict()'ed the object from a session, but this does not appear to be the case. It appears that the collection is aware of the fact it was loaded and then changed, thus it tries to do an update on the "target" datasource instead of an insert.

I am hoping to see if there is a way to have hibernate NOT inject its proxy classes, but at the same time I am wondering if these types of migrations across datasource sessions are a good use case for Hibernate in general.