从级联删除连接表与@ManyToMany注解

本文介绍了从级联删除连接表与@ManyToMany注解的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

您好我有一个问题，我的映射实体。我使用JPA2和Hibernate实现。我的表与@ManyToMany注释

Hi I got a problem with mapping my entities. I'm using JPA2 and Hibernate implementation. I got tables with @ManyToMany annotation

img204.imageshack.us/img204/7558/przykladd.png

我映射的：

@Entity @Table("employee") class Employee { @Id   @GeneratedValue(strategy = GenerationType.IDENTITY)   private Integer id;   @Column   private String name;   @ManyToMany   @JoinTable(name = "proj_emp",    joinColumns = @JoinColumn(name = "employee_id", referencedColumnName = "id"),   inverseJoinColumns = @JoinColumn(name = "project_id", referencedColumnName = "id"),               uniqueConstraints = @UniqueConstraint(columnNames = {"employee_id", "project_id"}))    private List<Project> projects;                ...} @Entity @Table("project") class Project {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Integer id;     @Column     private String name;               @Column        private Integer budget;            @ManyToMany(mappedBy = "projects")         private List<Employee> employees;                ...}

现在我想有一个级联从表中删除proj_emp当我从员工中删除记录，但是从表项目没有什么可以被删除。

Now I would like to have a cascade deleting from table proj_emp when I delete records from Employee, but nothing from table Project can be deleted.

什么是收购的最佳途径？

What is the best way to acquire that?

谢谢的Dawid

Thanks Dawid

推荐答案

您可以将您的@ManyToMany分成@一对多，多对一，并成立了级联样式如图所示的此处虽然问题使用Hibernate的会话，你可以使用JPA的EntityManager。或者使用新的JPA功能 @ElementCollection （仅JPA 2）来映射你的加入类。请参见这里如何。仅仅通过更换@ElementCollection Hibernate的@CollectionOfElements

You can split your @ManyToMany into a @OneToMany-ManyToOne and set up a cascading style as shown here Although the question uses Hibernate's session, you can use JPA EntityManager. Or use the new JPA feature @ElementCollection (Only JPA 2) to map your joined class. See here how to. Just replace Hibernate's @CollectionOfElements by @ElementCollection