跨2個實體搜索JPA

Question

我有兩個JPA連接的實體，Game和GameScore。如果玩家加入遊戲，則爲他製作新的GameScore。但是我需要獲得不加入玩家的遊戲（沒有GameScore）。我該怎麼做？我嘗試了NamedQueries和CriteraBulder，但沒有結果。

遊戲endity：

package prayForHunt.model; 

import java.io.Serializable; 
import java.util.Date; 
import java.util.List; 
import javax.persistence.*; 
@Entity 
@NamedQueries({ 
@NamedQuery(name = Game.Q_GET_ALL_GAMES, query = "SELECT c FROM Game c"), 
}) 
    public class Game implements Serializable { 

//-------------------------------------------- 
@Id 
@GeneratedValue 
private int gameId; 
//--------------------------------------------  
@OneToMany(cascade = CascadeType.ALL, mappedBy = "game") 
private List<GameScore> gameScore; 
} 

GameScore實體

package prayForHunt.model; 

import java.io.Serializable; 
import java.util.List; 
import javax.persistence.*; 
import javax.persistence.metamodel.SingularAttribute; 

@Entity 
@NamedQueries(
@NamedQuery(name = GameScore.Q_GET_ALL_GAMESCORE, query = "SELECT c FROM GameScore c") 
) 
public class GameScore implements Serializable { 

@Id 
@GeneratedValue 
private int gameId; 
@ManyToOne 
protected Game game; 
@ManyToOne 
protected Player player; 

} 

Answer 1

那麼，什麼是需要的結果是所有的遊戲實體，其中在gameScore 爲空這樣的實例。 JPQL查詢獲取遊戲沒有得分（也可以命名查詢使用）：

SELECT g FROM Game g WHERE g.gameScore IS EMPTY 

等效條件查詢如下：

CriteriaBuilder cb = em.getCriteriaBuilder(); 
CriteriaQuery<Game> cq = cb.createQuery(Game.class); 
Root<Game> member = cq.from(Game.class); 
cq.select(member) 
    .where(cb.isEmpty(member.<Collection>get("gameScore")));   
em.createQuery(cq).getResultList();