User development, A new message was posted in the thread "Weird usage of @ElementCollection": http://community.jboss.org/message/524306#524306 Author : Juergen Zimmermann Profile : http://community.jboss.org/people/Juergen.Zimmermann Message: -------------------------------------------------------------- @ElementCollection is a new annotation of JPA 2, and is provided by Hibernate 3.5-beta4. I tried to use this feature in an entity class:   @Entity public class Customer implements Serializable {    @Id    ...    @ElementCollection(fetch=EAGER)    @CollectionTable(name="customer_code", http://community.jboss.org/mailto:joinColumns=@JoinColumn(name=&quot;...)    @Column(name="code_fk")    private Set<Integer> codes; }   However, the concrete type of attribute "codes" is Hibernate's PersistentSet, so that "codes" cannot be updated outside of a transaction, e.g. via checkboxes in JSF based pages. Therefore, I extended the entity class:   @Entity public class Customer implements Serializable {    @Id    ...    @ElementCollection(fetch=EAGER)    @CollectionTable(name="customer_code", http://community.jboss.org/mailto:joinColumns=@JoinColumn(name=&quot;...)    @Column(name="code_fk")    private Set<Integer> codesDB;    @Transient    private Set<Integer> codesUI; }   Now, I can update the transient attribute codesUI in the JSF pages. But, new problems arrived: a) "codesUI" CANNOT be instantiated via +*@PostLoad*+ when reading a Customer object from the database - maybe because codesDB is considered as an association. OK, so I extended the get method for codesUI to instantiate it from codesDB. b) "codesDB" CAN be instantiated by *+@PrePersist+* when persisting a new Customer object via EntityManager.persist(). Fine. c) "codesDB" CANNOT be updated by *+@PreUpdate+* when an existing Customer object is updated via EntityManager.merge(). When the @PreUpdate method is invoked the "codesUI" attribute suddenly is null. Thus for updates I have to modify my DAO method, but for new creations everything works fine through @PrePersist...   Any hint or comment is highly appreciated! -------------------------------------------------------------- To reply to this message visit the message page: http://community.jboss.org/message/524306#524306