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POIs it legal to replace a list by an other one in an Hibernate JPA entity?
 

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  1. POIs it legal to replace a list by an other one in an Hibernate JPA entity?
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    <p>Assume a Hibernate 4.2 JPA 2.0 entity <code>class EntityA</code>, it contains a <code>@ManyToOne</code> field <code>List&lt;EntityB&gt; bs</code>. Up to now I strongly believed that I must not replace <code>bs</code> by an <code>new</code> List, instead I have to use the list methods <code>clear</code>, <code>add</code> and <code>remove</code>.</p> <p>To day I wanted to show a college that it will cause problems when I replace the List with an new one, but nothing strange happed, it worked, the database and the entity was updated correctly. Now I am confused: <strong>Is it with the hibernate 4.x JPA 2 allowed to replace a collection of an persisted entity?</strong></p> <p>The two enities, with a OneToMany relation ship, maintained by the one-site.</p> <pre><code>@Entity public class EntityA { @Id long id; @OneToMany public List&lt;EntityB&gt;bs; } @Entity public class EntityB { @Id long id; hashCode and equals based on id } </code></pre> <p>The test, that did not find a problem</p> <pre><code>@Test @Transactional public testReplaceSet { //given: a persistent entity a that contains a persistent entity b1 EntityA a = this.entityManager.persist(new EntityA()); EntityB b1 = this.entityManager.persist(new EntityB()); a.bs = new ArrayList(); a.bs = b1; this.entityManager.flush(); //when: assining a NEW List with an new persistent Entity b2 EntityB b2 = this.entityManager.persist(new EntityB()); a.bs = new ArrayList(); a.bs = b2; long aId = a.id; this.entityManager.flush(); this.entityManager.clear(); //then: the collection is correct stored EntityA AReloaded = this.entityManager.find(EntityA.class, aId); //here I expected the failure, but there was no! assertEquals(b2, AReloaded.bs.get(0)); } </code></pre>
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    1. USRalph
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    1. COTry the modification starting EntityB b2 = this.entityManager.persist(new EntityB()); in a new txn. I'm not sure hibernate is so strict as to use words like "allowed" or "legal" but I've certainly had exceptions with that pattern.
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      1. USTaylor
    2. COHow are the entity ids being set? If they are the same assertEquals should return true.
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    3. CO@Thiago Gama: good idea, but they are set correctly
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      1. USRalph
 

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