Saving parent and child in separate transactions with JDO (Datanucleus)

Question

I have a 1:n related parent and child object. The use case is such that I'd always persist a parent record before I persist one or more child records. When I save the child, it always attempt to re-create the parent record, even though it has been saved. How do I prevent that?

Parent class:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Parent {

    @PrimaryKey
    @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY)
    private long id;
...}

Child class:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Child {

    @PrimaryKey
    @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY)
    private long id;
        
    @Persistent
    private Parent parent;
..}

Saving code:

Transaction tx = pm.currentTransaction();
try {
    tx.begin();
    pm.setDetachAllOnCommit(true);
    pm.makePersistent(parent);
    tx.commit();
} finally {
    if (tx.isActive()) {
        tx.rollback();
    }
    pm.close();
}
...
Child child = new Child();
child.setParent(parent); // reference the saved parent
tx = pm.currentTransaction();
try {
    tx.begin();
    pm.setDetachAllOnCommit(true);
    pm.makePersistent(child); 
    tx.commit(); // here the parent is saved again
} finally {
    if (tx.isActive()) {
        tx.rollback();
    }
    pm.close();
}

When that executes, I am expecting an insert just on the child table. But instead I am also seeing an insert on the parent as well.

Answer 1

Problem solved. It turns out I need to have "detachable=true" in my class declaration:

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class Child {