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using EntityManager in @ViewScoped bean is a terrible idea. In a clustered setup, EM will try to be serialized to other cluster nodes, which will fail miserably and will cause session loss.
I use a CDI EM producer pattern and inject that instead. It's serializable and because it @ApplicationScoped, and call a get method on that to get an appropriate EM from the @ViewScoped bean.
Posted by Lenny Primak on May 11, 2016 at 05:33 PM CEST #
Batch fetching is very useful JPA optimization technique. It's used to solve N+1 issues in an efficient manner, when as opposed to join fetch, you need to retrieve multiple rows (@OneToMany) where you can retrieve using IN (1,2,3,4) etc. instead of using multiple select statements one by one
Posted by Lenny Primak on May 11, 2016 at 05:54 PM CEST #
thanks! I mentioned fetch joins in earlier airhacks editions. I was not aware that Fetch Joins are also known under the name "Batch Fetching".
Fetch Joins are very useful:
FROM Department d LEFT JOIN FETCH d.employees
WHERE d.deptno = 1
(from the spec, chapter 22.214.171.124),
thanks and see you next month!,
Posted by 192.168.0.91 on May 11, 2016 at 07:07 PM CEST #