将级联类型删除应用于许多关系

Question

我目前正在开发网络票务系统，并有可以存储我的机票数据的课程。每张票都可以具有与之关联的多个标签，并且要管理我创建标签编辑器的那些标签。这很好，只有一个删除选项仍缺少。到目前为止，大多数删除都没有解释该标签仍由另一张票参考，该票证需要先删除它。在找到解决方案的过程中，我遇到了cascadeType.delete，这似乎是我所追求的。

但是，由于票务对象包含一组标签，而不是相反，每次我删除票证时，所有标签都会消失，而不是相反。在阅读了CascadeType的文档后，这似乎很明显，但是我现在毫无头绪如何实现相反的效果。我想到只是对使用我的标签的所有门票创建参考，尽管这似乎是两次存储相同的数据。

我的门票看起来像这样：

@Entity
@Data
@NoArgsConstructor
public class Ticket {
    @Id
    @Column(length = 40)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(nullable = false)
    private String title;

    @OneToMany(targetEntity = TicketEntry.class, mappedBy = "ticket", orphanRemoval = true, fetch = FetchType.EAGER)
    private List<TicketEntry> entries = new ArrayList<>();

    @Column
    private Status status = Status.OPEN;

    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "ticket_labels",
            joinColumns = { @JoinColumn(name = "ticket_id")},
            inverseJoinColumns = { @JoinColumn(name = "label_id" )}
    )
    private Set<TicketLabel> labels = new HashSet<>();
}

还有这样的标签：

@Entity
@Data
@NoArgsConstructor
public class TicketLabel {

    @Id
    @Column(length = 40)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    private String name = "";

    @EqualsAndHashCode.Exclude
    @ToString.Exclude
    @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.REMOVE)
    @JoinTable(name = "ticket",
            joinColumns = { @JoinColumn(name = "label_id")},
            inverseJoinColumns = { @JoinColumn(name = "ticket_id" )}
    )
    private Set<Ticket> tickets = new HashSet<>();
}

但这仍然不起作用。我是否需要在标签对象中参考所有门票？还是我可以以某种方式使用“反向删除”级联类型？

Answer 1

您的多对多映射意味着您有两个相交表票和ticket_labels。我敢打赌你不想要那个，你只需要一个。 For bidirectional mapping you may have:

public class TicketLabel {
//...
   @ManyToMany(mappedBy = "labels", cascade {CascadeType.MERGE, CascadeType.PERSIST})
   private Set<Ticket> tickets = new HashSet<>();
}
//...

and

public class Ticket {
// ...
   @ManyToMany
   @JoinTable(name = "ticket_labels",
       joinColumns = { @JoinColumn(name = "ticket_id")},
       inverseJoinColumns = { @JoinColumn(name = "label_id" )}
   )
   private Set<TicketLabel> labels = new HashSet<>();

   public void removeLabel(Label label) {
      labels.remove(label);
      label.getTickets().remove(this);
   }

   public void addLabel(Label label) {
      labels.add(label);
      label.getTickets().add(this);
   }
// ...
}

You have to manually synchronize labels and tickets by helper remove and add methods as explained in