Let's say there are entities like Thing and ThingItem with an 1:N relationship. Imagine that there are hundreds of items and they have some attributes which are important and tedious to set. There should be some ThingBackup gathering all changes to all items belonging to a single Thing (they get written as a blob for simplicity).
I'm doing it using hibernate listeners, so that I don't have to add code to all program parts doing the change. It works well, but I don't know how to ensure consistency.
I thought, I'd use POST_UPDATE (as opposed to POST_COMMIT_UPDATE), so that both the items and the backup get written in the same transaction.
The problem is that in a PostUpdateEventListener, doing session.createCriteria(ThingBackup.class). ... .uniqueResult() leads to a ConcurrentModificationException in hibernate. The problem seems to be that the listeners get called from a loop iterating the list of changes and this very list gets modified when accessing the database (even on a read access as it requires some flushing).
I'd call it a bug, thought it does not violate the specification (given exactly zero lines of Javadoc, there's not much to violate). It may get fixed one day or not, I need a workaround. It looks like an older version of hibernate manifested a different bug in this place.
I can create another session and use it for the needed work (read the ThingBackup, modify it and write it back). However, this way I get two transactions and, in case the one closed last fails, an inconsistency.
Is there a solution? Or am I maybe doing something wrong?
