[jboss-user] [EJB 3.0] - Re: onetomany relationship question
Hi, I played around with your sample a bit. I agree that it works if you first create and save the parent, then create the child, set the parent and persist the child. But assume that you don't save the parent, but the child. Here is the code snippet: ParentBean parent = new ParentBean(); | entityManager.persist(parent); | | | ChildBean child1 = new ChildBean(); | parent.getChilds().add(child1); | //child1.setParent(parentNew); | | entityManager.persist(parent) | In this case, child and parent will be saved without error messages, but the relationship related database data is missing. So, as a general guideline: always update both sides of the relationship, this will avoid a lot of problems ;-). Best regards Wolfgang View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4242479#4242479 Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&p=4242479 ___ jboss-user mailing list jboss-user@lists.jboss.org https://lists.jboss.org/mailman/listinfo/jboss-user
[jboss-user] [EJB 3.0] - Re: onetomany relationship question
ok it seems that my test cases were erroneous.
i finally got the onetomany to fetch the 'many' by refreshing the entity. This
then invoked the following query
| hibernate: select childbean0_.ID as ID3_, childbean0_.parent_ID as
parent2_3_ from ChildBean childbean0_ where childbean0_.parent_ID=?
|
my test code also shows that the relationship only needs to be set on the many
side.
|
| @Test
| public void one2manyTestWithSettingManySide() {
|
| ParentBean parent = new ParentBean();
| entityManager.persist(parent);
| long id = parent.getId();
|
| ChildBean child1 = new ChildBean();
| child1.setParent(parent);
| entityManager.persist(child1);
|
| ChildBean child2 = new ChildBean();
| child2.setParent(parent);
| entityManager.persist(child2);
|
| Query query = entityManager.createQuery("from ChildBean child
where parent.id=:id");
| query.setParameter("id", id);
| List resultList = query.getResultList();
| assertEquals( 2, resultList.size() );
|
| //check refresh
| entityManager.refresh(parent);
| assertEquals( 2, parent.getChilds().size() );
|
| ParentBean parentBean = entityManager.find(ParentBean.class,
parent.getId());
|
| assertEquals( 2, parentBean.getChilds().size() );
|
| }
|
|
thanks for your help wolfgang.
-lp
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[jboss-user] [EJB 3.0] - Re: onetomany relationship question
Hi, actually, the "to many" side should be automatically populated when you access it. So, there is no need to perform entity manager queries. Depending on the fetchType of the relationship, different things might happen: If fetchType is "EAGER", then the children will be loaded when the parent is loaded. In this case, the EntityManager will fire some join statement against the database to load parent and childs with one query. If fetchType is "LAZY", then the first call to "parent.getChilds()" will trigger the child collection loading. This will only work if the parent entity is under EntityManager control. Hope this helps a bit. Wolfgang View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4242194#4242194 Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&p=4242194 ___ jboss-user mailing list jboss-user@lists.jboss.org https://lists.jboss.org/mailman/listinfo/jboss-user
[jboss-user] [EJB 3.0] - Re: onetomany relationship question
thanks for the rapid response wolfgang. i added the SQL tracing but there is *no* SQL when calling parent.getChilds(). So if i have understood the 'onetoMany' relationship, it doesnt populated the 'many' unless it has been explicitly set using the parent.setChilds(). This seems an almost pointless relationship. In order to get the list of childs from existing data (ie.reference data), one must use a join query like | em.query( 'from Child child where child.parent_id=:id') | I was hoping the above would be executed during the retrieval of the 'many'. Q1. what exactly is the point of the 'onetoMany' if it is only useful if used when explicitly setting the collection on the 'one' side? any help to clarify the above is most appreciated. -lp View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4242160#4242160 Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&p=4242160 ___ jboss-user mailing list jboss-user@lists.jboss.org https://lists.jboss.org/mailman/listinfo/jboss-user
[jboss-user] [EJB 3.0] - Re: onetomany relationship question
Hi, Q1: for each child, you have to do this: ParentBean parent = ...; | ChildBean child1 = ...; | ==> parent.getChilds().add (child1); | child1.setParent(parent); | Otherwise, the relation will not be saved, but there will be no error message. Q2: I don't know what is happening if you call "setChilds" before loading them, but I would expect strange side effects at least when the collection is under EntityManager control (inside a session bean method/transaction). So better manipulate the collection returned by "getChilds" and add/remove items. I will give this a try in the next few days and update my Wiki if I find a "No go". Q3: Did you activate SQL query logging in your persistence.xml? | http://java.sun.com/xml/ns/persistence"; | xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; | xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"; | version="1.0"> | | ... | | ... | ===> | | | | But I am not sure how the childs are loaded. I will take a look at the JBoss console when I near a computer with JBoss ;-) Best regards Wolfgang View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4242128#4242128 Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&p=4242128 ___ jboss-user mailing list jboss-user@lists.jboss.org https://lists.jboss.org/mailman/listinfo/jboss-user
