java - 使用 IdClass 连接表

Question

在我的项目中，实体的结构如下。

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

对于用作 PK 的好友实体 - 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;

    ...
}

问题是我无法加入 findFriendsByUser 方法。

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();
}

我发现了这个异常:

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

使用注解@Embeddable的唯一解决方案？

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

这里不是这种情况，类型不同!