What I'm trying to do is to determine what values have been modified, prior to persisting the object to the database (for logging purposes).

The question I have is when does the first level cache get updated with modified data. Here is what I'm doing :

1) I read an object :



2) I change a value on my object :


3) Later on, within the same JTA transaction, and before I actually persist / flush my changes, I do another read from the database :



4) I then attempt to determine what has changed between the two versions of this Subject object :

5) My confusion lies in the fact that both these debugs print 'Bill', when what I expect is the oldSubject1.getFirstName() to return the value from the database.

I was under the impression that my subject1 values wouldn't be persisted to the cache or the database until I do an em.persist(subject1) and a flush.

Is there something I'm missing with regards to when the values are flushed to the first level cache and/or the database? When I do my second read I would expect to get the old value that's in the database, even though I'm still in the same transaction.

Any help / clarification would be greatly appreciated.

I'm using Hibernate 3.2.2 with an oracle 10g database.

Step 1.
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Subject object is being read from DB and your first level session is getting populated with this object.

Step 2.
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Since you are changing the one attribute in the object, the value present in the session is also getting updated.

Step 3.
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This would merge your value from DB with the session and return the same object. So after this step subject1 and oldSubject1 are really pointing to the same object.

Step 4.
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Expected behavior.

Thanks

Why / how is the session being updated when I change a value in my Subject object, shouldn't I have to do a flush() or persist() before the session is updated with the new value?

Is it possible to get the old value (pre flush) out of the database for this object, since I need to be able to determine what has changed between the old and the new Subject records?

Session is getting updated because it is the same java object.
flush() doesnt update session, it merges the session value with DB value.

One way (there could be other ways also) to have your pre change values would be like this
1. Read the object.
2. Evict the object from the session. This object will now have the old values.
3. Read the object again to a diff java object.
4 make changes to this new java object.

Perform the comparison among these 2 java objects.