I'm trying to achieve something like the following, using the JPA Criteria API:

SELECT b FROM Box b JOIN SpecialItem s WHERE s.specialAttr = :specialAttr

The objects are

Box

@Entity
public class Box implements Serializable {
  ...
  @ManyToOne
  @JoinColumn( name = "item_id" )
  Item item;
  ...
}

Item

@Entity
@Inheritance( strategy = InheritanceType.JOINED )
public class Item implements Serializable {
  @Id
  private String id;
  ...
}

SpecialItem

@Entity
public class SpecialItem extends Item {
  private String specialAttr;
  ...
}

My attempt

EntityManager em = getEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery( Box.class );
Root from = cq.from( Box.class );

// Nothing to specify SpecialItem over Item!      
Join join = from.join("item", JoinType.LEFT);

// java.lang.IllegalArgumentException: Unable to 
// resolve attribute [specialAttr] against path [null]      
Path p = join.get( "specialAttr" );

Predicate predicate = cb.equal( p, "specialValue" );
cq.where( predicate );

Not surprisingly it throws an exception because specialAttr isn't a member of class Item.

How can I return all the Boxes that contain a SpecialItem, where the SpecialItem.specialAttr has some value?

jpa criteria-api
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