Unable to read changes before commit

Question

I have a mix of insert and select statements for a particular transaction operation.
I need to insert to table 1 a set of five records. ie. five inserts to table 1.
Then i need to sum up a column in table 1, this may have certain records which were inserted recently and some might be older ones.
This sum needs to be inserted into another table 2.
In my code i maintain the sequence of inserting, fetching the sum and inserting. I confirm the sequence by giving System.out.println().
But since everything runs inside a container managed external transaction controller.
Even though i see the System.out.println's in proper sequence, the suming query is happening before.
At the end, i have Before JTS completion, followed by my insert sqls, followed by After JTS completion.
Clearly the problem is, the fetch is happening before i insert, in JTS.
So how do i make sure, that the fetch happens after my first insert.

Answer 1

I assume that you are using the TopLink UnitOfWork. The UnitOfWork defers committing all changes to the database until the commit (beforeCompletion in JTA), so any queries you perform will not see any of these changes until after the commit. It does this to optimize the commit, maintain referential integrity, avoid deadlocks, avoid holding pooled connections, etc.
You must either:
- perform the inserts and the sum query in two separate transactions
- compute the sum from the objects in memory
- use a database session and insertObject instead of a unit of work
To compute the sum in memory you may wish to use a conforming query in TopLink to query the new objects that have not yet been inserted to the database.
In the 10.1.3 release, there will be support for a non-deferred unit of work, and a writeChanges() unit of work API to write changes before the commit.