Is there any way in OpenJPA to get hold of a nested object property via CriteriaBuilder?

Here's a small case.

```
@Entity
public class X {
       private Object Y;

       // getters, setters...
}

@Entity
public class Y {
       private String Z;

       // getters, setters...
}

```

So, when using CriteriaBuilder, we use X as Root, i.e.:

```
@PersistenceContext
private EntityManager entityManager;

//.....

Root<X> rootObj = criteriaBuilder.from(X.class);
CriteriaQuery<X> select;

String param1 = X.getY().getZ();

// initializing predicate, default value is TRUE
Predicate predicate1 = criteriaBuilder.isNull(null);

// construct search predicate which fails miserably due to IllegalArgumentExecption
if (X != null) {
    predicate1 = criteriaBuilder.and(predicate1, criteriaBuilder.equal(rootObj.<String> get("Y.Z"), param1));
}

```

Now, my grief is this -> `get("Y.Z")`

CriteriaBuilder doesn't know to fetch Z reflectively (however it can and will resolve Y). Is there any way to get hold of Z directly from get()?

Apart from using JPQL, I can think of one other method - which I dislike immensely: I suppose I could have exposed Z as an `@Transient` property in X (as to prevent OpenJPA from persisting it as a column), but that sounds like a Really Bad Idea: I am essentially flattening out an object graph manually and introduce unneeded garbage inside the entity bean, not counting the time needed to flatten out a complex graph or the error-proness of this (it can go awry in so many ways).

Is there a way to make this work? Any ideas are appreciated.