I have an entity which contains several basic fields A, B and C and one complex field X which is not (should not be) mapped to a database column. The idea is to create X from A, B and C when loading an instance, and to deconstruct X into A, B and C when persisting.

The first logical thing to try was something like:

@Entity
class Xxx
{

private String a;

@Transient
private X x;

@PrePersist
public void prePersist()
{
XParts xp = x.deconstruct();
a = xp.getA();
//...
}
//...
}

The problem is, when calling entityManager.merge(xxx); x is lost. Something to do with how the @Transients are handled in JPA. @Transient and @PrePersist don't mix. Ok. Can't argue with the specification I guess.

But, what are the alternatives? I really don't need X in database.

The best I could come up with is:

@Column(insertable=false,updatable=false)
private X x;

Which creates column X, which is always null. If it's really the only way, I can live with that, but it seems hackish at best.

I can't be the only one who run into this problem. Is there any better way to do this?

Or maybe - that would be preferable - there is a way to make @Transient and @PrePersist work together?