EclipseLink merge unexpected cascade

问题

I have two entity classes user and device.

User entity:

public class User {
    private Long userId;

    @OneToMany( mappedBy = "userId", fetch = FetchType.LAZY)
    private Collection<Device> deviceCollection;

and device entity:

public class Device implements Serializable {
    @JoinColumn(name = "user_id", referencedColumnName = "user_id")
    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    private User userId;

When I merge a previously detached device entity into the entity manager after the parent user has been deleted, both the (previously removed) user and the device are re-inserted into the database. There is no cascade annotation on user or device entity; therefore, I don't expect the user entity to be reinserted but it did;

How do I prevent the merge operation to cascade to the user entity?

Thanks in advance.

回答1:

Any changes you do in detached state there is no possible way for Session Manager to know it so for it the changes are always new objects that needs to be merged (If you are calling merge)

So when you call merge it will load it from database so your object will have Prev+ new changes. So that is why mentioned behavior is happening.

What you can do is first load entity in the session apply changes and then call merge.

What you can do is something like below I have used similar relationship in one of my project with Eclipse Link

Query query = entityManager
            .createNamedQuery("User.FindByUserId");
    User fromDatabase = null;
    try {
        query.setParameter("userId", device.getUser().getUserId());
        fromDatabase = (User) query.getSingleResult();

    } catch (NoResultException noResultException) {
        // There is no need to do anything here.
    }
    if (fromDatabase == null) {
        User user= entityManager.merge(device.getUser());
         device.setUser(user);
    } else {
        device.setUser(user);
    }
    entityManager.persist(device);

回答2:

Try adding insertable=false, updatable=false to your JoinColumn, e.g.

@JoinColumn(name = "user_id", referencedColumnName = "user_id", insertable=false, updatable=false)

回答3:

You should be using a version number to prevent entities from being mistakenly resurected. This will force an exception, where as the specification is a bit unclear on what should happen when merging over a relation that isn't marked cascade all or merge. The spec states that managed entities will be synchronized to the database, while the section dealing with merge implies that even entities referenced by relations without the cascade merge/all options will be managed afterward. This behavior is probably not what was intended, but shouldn't be relied on until clarified.

回答4:

I had the same problem and I found a bug about this: EntityManager.merge() cascading by default but I really don't understand why this behaviour was never fix. It is one of reasons among others that I don't use EclipseLink (But it's not the point here)

Edit:

Chris, the comment which begin with "I'm not an expert" the argument that is put in head is not right, I think. What I understand, it's just that entity with a relation without cascade=MERGE or cascade=ALL, you can just navigate, that's all.

Otherwise why use Merge annotation ? It doesn't make sense.

来源：https://stackoverflow.com/questions/11957461/eclipselink-merge-unexpected-cascade

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