ManyToOne reference loading with JPA/Hibernate

In this example an InvestigationType has many SampleType’s. If I load an InvestigationType via em (entity manager) find it also loads the samples.

1.	InvestigationType inv2 = (InvestigationType) em.find(
2.		InvestigationType.class, inv.getId());
3.	System.out.println("Inv2 ID="+inv2.getId());
4.	System.out.println("Inv2 Title="+inv2.getTitle());
5.	assertTrue(inv2.getSample().size() == 2);

However, if I load a SampleType the investigation field is null, unless I refresh the object.

1.	// Get a sample
2.	SampleType s3 = (SampleType) em.find(
3.		SampleType.class, inv2.getSample().get(0).getId());
4.	em.refresh(s3);
5.	System.out.println(convertDataToXmlString(s3));
6.	InvestigationType inv3 = s3.getInvestigation();
7.	assertNotNull(inv3);

From my understanding I should not have to do this as the fetching should be the same in both instances, ie resolving the parent by default. Similarly, if I query for both objects the references are correctly loaded.

List items = em.createQuery("SELECT i, s FROM s,
     IN(s.investigation) i WHERE").getResultList();

If someone could tell me why this is so, please let me know. Else, at least I have a working example now.

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One Response to ManyToOne reference loading with JPA/Hibernate

  1. shumy says:

    You can use AspectJ to change your get/set methods without changing the (generated) code directly.

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