如何在雙向關系中刪除一側的對象？

Question

我想從一邊刪除關系。 讓我解釋。

我的數據庫看起來像這樣：

我將我的存儲庫建立在JPARepository 。

我有兩個實體Team和Player 。

Player實體看起來像這樣：

@Entity
    @Table(name = "PLAYER")
    public class Player implements Serializable, Comparable<Player>{
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy=GenerationType.AUTO)
        private Long id_player;

        @Size(min=3, max=20)
        private String name;
        @Size(min=3, max=20)
        private String surname;
        @Size(min=3, max=20)
        private String position;
        @Min(value=10) 
        private int age;
        @Min(value=1)
        private int number;

        @ManyToOne(fetch = FetchType.LAZY)
        @JoinColumn(name = "id_team")
        private Team team;
        //getters and setters
    }

......和Team實體：

@Entity
@Table(name = "TEAM")
public class Team implements Serializable, Comparable<Team>{
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id_team;
    @Size(min=4, max=20)
    private String name;
    @Size(min=4, max=20)
    private String city;
    private int goals_hit;
    private int goals_lost;
    private int points;
    private int ranked;

    @OneToOne(cascade = CascadeType.MERGE)
    @JoinColumn(name = "id_coach")
    private Coach coach;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id_stadium")
    private Stadium stadium;

    @OneToMany(mappedBy = "team", fetch = FetchType.LAZY)
    private List<Player> playerList;

    @OneToMany(mappedBy = "team", fetch = FetchType.LAZY)
    private List<TeamChoosenDate> teamChoosenDateList;
    //getters and setters
}

因此， Player包含與Team一個關系，但Team包含一個Players List 。

教練可以編輯他的團隊，例如他想要從Team刪除Player （ Team - > Player之間的關系），但不要失去Player （因為他與其他表有關系 - Events ）。

總之：從正確的Team刪除Player ，但不要丟失Player對象。

我怎樣才能做到這一點 ？

我的嘗試：我從List刪除Player ，但每次重新加載時 - 他都回來了......下面的方法顯示了我是如何做到的：

public void deletePlayerFromTeamPlayerList(Long idTeam, int idPlayer){

    Team team = teamRepository.findOne(idTeam);
    Player playerTmp = playerRepository.findOne( (long) idPlayer);

    List<Player> playerList;

    int indexOfFindedPLayer;


    playerList = team.getPlayerList();

    System.out.println("Before Delete: " + playerList.toString());

    indexOfFindedPLayer = playerList.indexOf(playerTmp);

    if(indexOfFindedPLayer >= 0){
        playerList.remove(indexOfFindedPLayer);

        System.out.println("After Delete: " + playerList.toString());

        team.setPlayerList(playerList);
        teamRepository.save(team);
    }
}

但是當元素被刪除時，在Player對象中id_team仍然是相同的（例如id_team = 2）

謝謝你的所有建議！

Answer 1

您可以通過以下方式更簡單地實現此目的：

public void deletePlayerFromTeam(int idPlayer){
    Player player = //loadPlayer;
    player.setTeam(null);

    playerRepository.save(player);
}

您也可以通過將player.team設置為null 並在集合上設置cascade來合並，從而在原始代碼中實現此目的：

@OneToMany(mappedBy = "team", fetch = FetchType.LAZY, cascade = CascadeType.MERGE)
private List<Player> playerList;

您應該始終確保關系的兩個方面保持一致。

Answer 2

使用此方法僅刪除一對多或多對一關系中的一側。

@ManyToOne(cascade=CascadeType.PERSIST, fetch = FetchType.LAZY)
//  @JoinColumn(name = "qid")
    @JoinColumn(name = "qid", referencedColumnName = "qid", foreignKey = @ForeignKey(name = "qid"), nullable = false)
    // @JsonIgnore
    @JsonBackReference
    private QueueGroup queueGroup;

這里CascadeType是所有事務所依賴的主要內容。