Hibernate createQuery()抛出ClassCastException,Transformer没有帮助

Question

尝试使用Hibernate 3.6和MySQL5.1选择一个实体,但我不断得到一个ClassCastException.

@Entity
@Table( name = "USER" )
public class User {
   @Id
   @Column(name= "user_id")
   private Long userId;

   @OneToOne()
   @JoinColumn(name="status_id")
   protected UserStatusType userStatusType;

   @OneToOne()
   @JoinColumn(name="region_id")
   protected Region region;


@Entity
@Table( name = "REGION" )
public class Region   
   @Id
   @Column(name = "region_id")
   private Long regionId


@Entity
@Table( name = "USER_STATUS_TYPE" )
public class UserStatusType  
   @Id
   @Column(name = "type_id")
   private Long typeId

在createQuery()中尝试使用HQL时,我不断收到ClassCastException:

session.beginTransaction();
User user = (User)session.createQuery(
   "from User u, UserStatusType ust, Region r "
   + " where u.userId = ? and u.userStatusType.typeId = ust.typeId"
   + " and u.region.regionId = r.regionId")
   .setLong(0, 42L)                     
   .uniqueResult();


 java.lang.ClassCastException:
[Ljava.lang.Object; cannot be cast to com.scd.dao.entity.User

我尝试使用setResultTransformer(Transformers.aliasToBean(User.class)),但这给了我一个NullPointerException.

不知道我做错了什么.

Answer 1

如果FROM子句包含多个实体,并且您只需要其中一个实体,请在SELECT以下位置指定:

User user = (User)session.createQuery(
    "select u "
    + "from User u, UserStatusType ust, Region r "
    + " where u.userId = ? and u.userStatusType.typeId = ust.typeId"
    + " and u.region.regionId = r.regionId")
   .setLong(0, 42L)
   .uniqueResult(); 

否则你将获得实体的元组Object[].

如果您确实需要提取而不是内连接,请使用JOIN FETCH:

User user = (User)session.createQuery(
    "from User u "
    + "join fetch u.userStatusType join fetch u.region "
    + " where u.userId = ?")
   .setLong(0, 42L)
   .uniqueResult();