Triggers implemented in TopLink

Question

I would like implement triggers in TopLink (instead of database). During UPDATE I need make the following steps:
1. modify attributes of the updated object
2. insert record into history table
The first step I have implemented in "aboutToUpdate" callback:
operatorMod = "John";
descriptorEvent.applyAttributeValuesIntoRow("operatorMod");
And it works.
For the second step I tried (in the same callback) insert new object into the current UnitOfWork, but the data was not stored into the database. I have used the following code:
UnitOfWork uow = (UnitOfWork)descriptorEvent.getSession();
KlientHistImpl kh = new KlientHistImpl("test");
uow.registerNewObject(kh);
How can I insert new object into "commiting" UnitOfWork (UnitOfWork with already started operation commit)?
Thanks in advance for any help.

Answer 1

Your options with this situation are:
- Adhoc SQL.
- Create a new Unit Of Work and use an external transaction controller so that the committing unit of work and your new unit of work will be governed by a JTA transaction.
- Explicitly manage the History as part of the application, not using the events.
- Use the pre update event (keeping in mind that (a) at this point in time the change sets for the UOW haven't been committed and (b) the event is fired to all registered objects, even those who haven't changed, so make sure you only register objects that you're going to change).
Based on the example you've shown, I recommend #3. I don't recommend people try to manage "historization" with events, unless it's just a simple ad-hoc SQL call you'd like to add. I would argue that if you have a class and have mapped it that you should treat it as a "equal citizen" in your app.
- Don