用IdClass加入表格

Question

在我的項目中，實體的結構如下。

public class FriendId { 
    private String profileFrom; 
    private String profileTo; 
    ... 
} 

For Friend實體用作PK - FriendId。

@Entity 
@Table(name = "FRIEND") 
@IdClass(FriendId.class) 
public class Friend { 
    @Id 
    @ManyToOne 
    @JoinColumn(name = "PROFILE_UUID_1", nullable = false) 
    private Profile profileFrom; 

    @Id 
    @ManyToOne 
    @JoinColumn(name = "PROFILE_UUID_2", nullable = false) 
    private Profile profileTo; 

    ... 
} 

問題是我不能加入方法findFriendsByUser。

public List<User> findFriendsByUser(String userUuid) { 
    CriteriaBuilder builder = getEntityManager().getCriteriaBuilder(); 
    CriteriaQuery<User> query = builder.createQuery(User.class); 
    Root<User> userRoot = query.from(User.class); 
    Join<User, Profile> profileJoin = userRoot.join(PROFILES); 
    Join<Profile, Friend> friendsJoin = profileJoin.join(FRIENDS); 
    Join<Friend, Profile> profileFriendsJoin = friendsJoin.join(PROFILE_TO); 
    Join<Profile, User> userFriendsJoin = profileFriendsJoin.join(USER); 
    Predicate userPredicate = builder.equal(userFriendsJoin.get(UUID), userUuid); 
    query.select(userRoot).where(userPredicate); 
    return getEntityManager().createQuery(query).getResultList(); 
} 

我捕獲這個異常：

java.lang.RuntimeException: java.lang.IllegalArgumentException: Unable to resolve attribute [profileTo] against path [null] 

唯一的解決方案使用註釋@Embeddable？

Answer 1

看看：http://docs.oracle.com/javaee/5/api/javax/persistence/IdClass.html

The names of the fields or properties in the primary key class and the primary key fields or properties of the entity must correspond and their types must be the same 

這不是這裏的情況，類型是不同的！