相关疑难解决方法(0)

我正在尝试使用JPA Criteria API实现以下类似的功能:

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

对象是

框

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

项目

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

SpecialItem

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

我的尝试

EntityManager em = getEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery( …