在对应的映射表中保存多对多关系 [英] save many-to-many relationship in corresponding mapping-table

问题描述

在我的Spring-Boot应用程序中，我想在数据库的对应映射表中保存用户角色多对多关系，但是休眠会给我一条错误消息.

in my Spring-Boot application i want to save a User-Role many-to-many relationship in a corresponding mapping-table in my database, but hibernate gives me an error message.

我的 User.java 类:

@Entity
@Table(name = "users")
public class User {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  Long id;
  String firstname;
  String lastname;
  String username;
  String password;

  @ManyToMany(mappedBy = "users")
  private Set<Role> roles;
}

我的 Role.java 类:

@Entity
@Table(name = "roles")
public class Role {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  Long id;
  String name;
  String description;

  @ManyToMany(cascade = CascadeType.ALL)
  @JoinTable(
          name = "role_users", 
          joinColumns = 
              @JoinColumn(name = "users_id", referencedColumnName = "id"), 
          inverseJoinColumns = 
              @JoinColumn(name = "roles_id", referencedColumnName = "id")
  )
  private Set<User> users;
}

我的运行方法:

@Override
@Transactional
public void run(String... strings) throws Exception {
    //add new Roles
    Role roleA = new Role("Rolle A");
    Role roleB = new Role("Rolle B");
    Role roleC = new Role("Rolle C");

    //add new Users
    User userA = new User("FirstnameA", "LastnameA", "UsernameA", "PasswordA");
    User userB = new User("FirstnameB", "LastnameB", "UsernameB", "PasswordB");

    //add new Lists of Roles
    Set<Role> rolesA = new HashSet<Role>();
    rolesA.add(roleA);
    rolesA.add(roleB);
    Set<Role> rolesB = new HashSet<Role>();
    rolesB.add(roleA);
    rolesB.add(roleC);

    //add a list of roles in one user, two times
    userA.setRoles(rolesA);
    userB.setRoles(rolesB);

    //save both users in db
    userRepository.save(userA); //rolle AB
    userRepository.save(userB); //rolle AC

    //give each role the corresponding user
    Set<User> usersA = new HashSet<User>();
    usersA.add(userA);
    usersA.add(userB);
    roleA.setUsers(usersA);
    roleRepository.save(roleA);
    Set<User> usersB = new HashSet<User>();
    usersB.add(userA);
    roleB.setUsers(usersB);
    roleRepository.save(roleB);
    Set<User> usersC = new HashSet<User>();
    usersC.add(userB);
    roleC.setUsers(usersC);
    roleRepository.save(roleC);

}

休眠在这方面给我一个错误消息:

Hibernate gives me an error message on that:

无法添加或更新子行:外键约束失败(projekt_gra.role_users，CONSTRAINT fk_roleusers_user外键(users_id)参考users(id)删除级联更新级联)

Cannot add or update a child row: a foreign key constraint fails (projekt_gra.role_users, CONSTRAINT fk_roleusers_user FOREIGN KEY (users_id) REFERENCES users (id) ON DELETE CASCADE ON UPDATE CASCADE)

我的构造来自

I have the construction from this site and it works with it, but in my code it doesn't work.

推荐答案

我总是通过将2个@ManToToMany关系重写为@OneToMany到一个新实体(将表传递给我)来解决这个问题.

I always pass this problem, by rewriting the 2 @ManyToMany relations to @OneToMany to a new entity which deliveres me the table inbetween.

一个很好的理由是，当我拥有@ManyToMany关系时，我永远无法轻易获得想要的东西，就像我得到的是Carthetic产品一样.将此表作为一个实体完全可以为我解决这个问题.

A good reason is that when I have @ManyToMany relations, I can never really easily get whatever I want, as I get carthetic products. Having this table inbetween as an entity totally removes this problem for me.

因此，总结一下:

• 您已经拥有您的 User 和您的 Role 类，这些都差不多
• 创建一个新实体: UserRole ，并具有以下属性:用户用户和角色角色
• 将 User 和 Role 中的两个@ManyToMany更改为@OneToMany的新@Entity UserRole
• 在 UserRole 中添加关系:2 @ManyToOne关系到 User 和 Role .

• You already have your User, and your Role class, those are almost OK
• Create a new Entity: UserRole, with properties: User user and Role role
• Change the two @ManyToMany in User and Role to @OneToMany's to your new @Entity UserRole
• Add the relations in UserRole: 2 @ManyToOne relations to User and Role.

您现在解决了这个问题，而且还有:可以查询关系UserRole.

You now got the problem gone, and extra: a posibility to query on the relation UserRole.

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