By default the autocommit value is false, therefore the transaction needs to be commited explicitly. This might be the reason why the changes not getting reflected in database, else can try flush to force the changes before commit.
When you close the session, then it will get commited in database implicitly [depends on the implementation].
When you have cascading transactions & needs to rollback for atomicity, you need to have control over transactions & in that case, autocommit should be false.
Either set autocommit as true or handle transactions explicitly.
Here is a good explanation on it.
Hibernate forum related to this.
Stackoverflow question on it.
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