@Entitylisteners

[motte1979]

Hi ,

Is there a seam-way to implement @Entitylisteners ? I've read in the book 'Java Persistence with Hibernate' that the user of EntityManagers is not allowed in callbacks. However; thats the usecase:

I've two Entities which are associated through a @ManyToMany association and i like to implement a last-save-wins-strategy for this set.

@Entity
@Table (name="t_foo")
@EntityListeners(value={Foolistener.class})
public class Foo {
 @Id
 private Long id;

 @Basic
 private String name;

 @ManyToMany (fetch=FetchType.LAZY)
 @JoinTable (name="t_foo_bar",
 joinColumns=@JoinColumn(name="foo_id"),
 inverseJoinColumns=@JoinColumn(name="bar_id"))
 private Set<Bar> bars;

.....

}

@Entity
@Table (name="t_bar")
public class Bar {
 @Id
 private Long id;
 @Basic
 private String name;
 @ManyToMany (fetch=FetchType.LAZY, mappedBy="bars")
 private Set<Foo> foos;

....
}

public class Foolistener {

 @PrePersist
 public void prePersist (Foo foo) {
 // delete the all entries in t_foo_bar which
 // reference too foo.getId()
 }

 @PreUpdate
 public void preUpdate (Foo foo) {
 // delete the all entries in t_foo_bar which
 // reference too foo.getId()
 }

}

The first issue on this is, that the callback is only called if the Entity-fields are changed, but not, if the included set changed only. Does anyone know why?
I know i could add a 'changed-set' - flag .. which is not very comfortable if the set is changed directly ;)

I tried to add @Name and @In annotations to the FooListener - but this seems not to work.

I've not much experience with Hibernate-jpa because i worked with jpox-jdo before. If i remember correctly it was no problem to have (restricted) database-access in callback-methods .

Any ideas ?

(see also http://www.jboss.com/index.html?module=bb&op=viewtopic&t=117557)[/url]

[motte1979]

Is there a better way than

Set<Bar> bars = new HashSet<Label>(foo.getBars());
foo.getBars().clear();
entityManager.merge(foo);
foo.setBars(bars);
entityManager.merge(foo);

?