Question

查看以下类（UNIdirectional @OneToMany）

@Entity
public class Team {

    private Integer id = -1;

    @Id
    @GeneratedValue
    public Integer getId() {
        return this.id;
    }

    private List<Player> playerList;


    @OneToMany
    @Cascade(CascadeType.SAVE_UPDATE)
    @JoinColumn(name="TEAM_ID", insertable=false, updateable=false)
    public List<Player> getPlayerList() {
        return this.playerList;
    }

    public void addPlayer(Player player) {
        player.setId(new PlayerId(getId(), getPlayerList().size()));

        playerList.add(player);
    }

}

注意addPlayer：团队的id和玩家的teamId引用相同的实例，所以

AssertEquals(team.getId(), player.getPlayerId().getTeamId());

应该工作，不是吗？

Hibernate不会保存-1值，因为我已经声明了生成器策略（默认为auto）如果声明了标识符生成器，Hibernate将负责主键值赋值。我已经确定-1为Team的id以命令在玩家的id中分享它的参考（当调用addPlayer方法时），如下所示

@Embeddable
public class PlayerId implements Serializable {

    private Integer teamId;

    private Integer playerIndex;

    // required no-arg constructor
    public PlayerId () {}

    public PlayerId(Integer teamId, Integer playerIndex) {
        this.teamId = teamId;
        this.playerIndex = playerIndex;
    }

    @Column(name="TEAM_ID", nullable=false)
    public Integer getTeamId() {
        return this.teamId;
    }

    @Column(name="PLAYER_INDEX", nullable=false)
    public Integer getPlayerIndex() {
        return this.playerIndex;
    }

    // getters and setters

    public boolean equals(Object o) {
        if(o == null)
            return false;

        if(!(o instanceof PlayerId))
            return false;

        PlayerId other = (PlayerId) o;
        if(!(getTeamId().equals(other.getTeamId()))
            return false;

        if(!(getPlayerIndex().equals(other.getPlayerIndex()))
            return false;

        return true;
    }

}

但是当我打电话时（特别注意一下addPlayer）

Team team = new Team();

Player player = new Player();

// teamId property in PlayerId references Team id
team.addPlayer(player);

session.save(team);

我看到我得到的数据库

PLAYER
TEAM_ID     PLAYER_INDEX
-1          0

TEAM
ID
1

保存后我比较

AssertEquals(team.getId(), player.getPLayerId().getTeamId()); // It does not works! why ?

日志输出

INSERT INTO TEAM VALUES()

// SELECT BEFORE SAVING OR UPDATING WHEN USING A COMPOUND PRIMARY KEY
SELECT * FROM PLAYER WHERE TEAM_ID = ? AND PLAYER_INDEX = ?

INSERT INTO PLAYER (TEAM_ID, PLAYER_INDEX) VALUES (?, ?)

所以你知道为什么Hibernate在保存一个团队及其球员之后在Player的teamId属性中丢失了Team的id引用？

Answer 1

我不确定“维护参考”是什么意思？我也不太清楚你在这里要做什么......

您是否希望Hibernate使用新创建的TEAM_ID实体的Team（例如在这种情况下为1）来插入Player个实例？如果是这样，你通过在@JoinColumn声明中将insertable / updatable指定为false来明确地防止这种情况发生 - 你需要在Player类中将它们移动到getTeamId()方法。

你能澄清一下你在这里想要达到的目标吗？

调用save后，Hibernate丢失了引用。你知道为什么吗？

1 个答案: