hibernate - EntityManager.flush(), EntityManager.getTransaction.commit(), What is the standard usage ? -

i'm trying understand how synchronisation between persistence context , database works.the code below runs pretty :

entitymanagerfactory factory = persistence.createentitymanagerfactory("projecta"); entitymanager em = factory.createentitymanager();  em.gettransaction().begin();  for(string name : names) {     student toinsert = new student();     toinsert.setname(name);     em.persist(toinsert); }  em.gettransaction().commit(); 

• but flush() method goes ? have use ?

• do have gettransaction.begin() everytime ?

• what standard form update information in database hibernate ?

1. flush not required commit flush automatically you. need flush when performing long running transaction data needs saved db avoid memory heap (or) if need sync data in session db reason.
2. if feel starting transactions tedious, ma use spring declarative transactions. doing so, spring take care of creating transaction boundaries around method , commits/rolls data depending on happens in method. easy use, has own limitations not allow handle rollback.
3. updating object depends on context of object(has 1 object in session/no object in session) use session.merge(object) solves couple of scenarios you. make sure, have data set on detached object needs saved, or else end deleting data not loaded.