java - Why does EntityManager.merge() prevent LazyInitializationException while EntityManager.find() don't? -


given following situation in web application:

// entitymanager em, 1 per request spring's openentitymanagerinviewfilter // parent oldparent, previous request (and therefore persistence context) parent parent = em.find(parent.class, oldparent.getid()); list<child> children = parent.getchildren(); // mapped collection lazyloading (child child : children) {      ...

the call of list iterator causes lazyinitializationexception. confusing, because fetching of list of children occurs in same persistence context (or wrong?). but, using merge(), works. if 2 request sharing 1 persistence context.

parent parent = em.merge(oldparent); list<child> children = parent.getchildren(); (child child : children) {      ... // no exception!!

what error in reasoning?

addition
i've proven error not caused parent.getid(). part of stacktrace:

at org.hibernate.collection.persistentlist.iterator(persistentlist.java:138)

that means iterator causes problem. , it's getting more weird - i've checked in first case (with find()), select statement issued hibernate retrieve new object database, not cache of persistence context.

addition2
here's bit more stacktrace:

org.hibernate.lazyinitializationexception: failed lazily initialize collection of role: edeka.sw.phb.model.chapter.subchapters, no session or session closed     @ org.hibernate.collection.abstractpersistentcollection.throwlazyinitializationexception(abstractpersistentcollection.java:380)     @ org.hibernate.collection.abstractpersistentcollection.throwlazyinitializationexceptionifnotconnected(abstractpersistentcollection.java:372)     @ org.hibernate.collection.abstractpersistentcollection.initialize(abstractpersistentcollection.java:365)     @ org.hibernate.collection.abstractpersistentcollection.read(abstractpersistentcollection.java:108)     @ org.hibernate.collection.persistentlist.iterator(persistentlist.java:138)     @ java.util.collections$unmodifiablecollection$1.<init>(collections.java:1022)     @ java.util.collections$unmodifiablecollection.iterator(collections.java:1021)     //... followed line of foreach.

i think problem not in iterating part because iterate new loaded parent. problem has .getid() seems not loaded merge works because dont call .getid()


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