hibernate - JPA2 多对多关系上的级联删除

Question

我已经阅读了很多关于级联和多对多关联的主题，但我一直无法找到我的特定问题的答案。

我在 UserProfiles 和 Roles 之间存在多对多关系。当我删除 UserProfile 时，我希望数据库删除连接表 (userprofile2role) 中的关联记录，因此使用实际的 SQL 'ON DELETE CASCADE' 操作。这可能吗？无论我尝试什么，Hibernate 总是在不指定 ON DELETE 行为的情况下创建 UserProfile 表。

用户配置文件映射:

@Entity
public class UserProfile {

    private Long id;
    private Set<Role> roles;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public final Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    // Note: CascadeType.ALL doesn't work for many-to-many relationships
    @ManyToMany (fetch = FetchType.EAGER)
    public Set<Role> getRoles() {
        return roles;
    }

    public void setRoles(Set<Role> roles) {
        this.roles = roles;
    }
}

角色映射:

@Entity
public class Role {

    private Long id;
    private Set<UserProfile> userProfiles = new HashSet<UserProfile>();

    @Id
    @GeneratedValue
    public final Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    // CascadeType.REMOVE doesn't create ON CASCADE DELETE in SQL?
    @ManyToMany(mappedBy = "roles", cascade = CascadeType.REMOVE)
    public Set<UserProfile> getUserProfiles() {
        return userProfiles;
    }

    public void setUserProfiles(Set<UserProfile> userProfiles) {
        this.userProfiles = userProfiles;
    }
}

不幸的是，由这些映射产生的连接表的 SQL 不包含 ON CASCADE DELETE 部分。我尝试在 UserProfile 中的角色集合和 Role 中的 userprofiles 集合上设置 CascadeType.REMOVE 行为(如图所示)，但无济于事。非常欢迎您的建议:-)

CREATE TABLE `px_userprofile2role` (
  `userprofile_id` BIGINT(20) NOT NULL,
  `role_id` BIGINT(20) NOT NULL,
  PRIMARY KEY (`userprofile_id`,`role_id`),
  KEY `FK1C82E84191F65C2B` (`userprofile_id`),
  KEY `FK1C82E8416203D3C9` (`role_id`),
  CONSTRAINT `FK1C82E8416203D3C9` FOREIGN KEY (`role_id`) REFERENCES `px_role` (`id`),
  CONSTRAINT `FK1C82E84191F65C2B` FOREIGN KEY (`userprofile_id`) REFERENCES     `px_userprofile` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=latin1

Answer 1

不支持生成 ON DELETE CASCDADE到 JPA 中的 DDL。级联 REMOVE 操作的概念不是 DDL 级别的构造。级联是关于将针对实体的生命周期操作级联到相关实体。它们与数据库中的级联几乎没有关系。在 JPA 2.0 规范中，这解释如下:

If X is a new entity, it is ignored by the remove operation. However, the remove operation is cascaded to entities referenced by X, if the relationship from X to these other entities is annotated with the cascade=REMOVE or cascade=ALL annotation element value.

If X is a managed entity, the remove operation causes it to become removed. The remove operation is cascaded to entities referenced by X, if the relationships from X to these other entities is annotated with the cascade=REMOVE or cascade=ALL annotation element value.

此外 REMOVE 不应与 @ManyToMany 一起使用(来自 JPA 2.0 规范):

The relationship modeling annotation constrains the use of the cascade=REMOVE specification. The cascade=REMOVE specification should only be applied to associations that are specified as OneToOne or OneToMany. Applications that apply cascade=REMOVE to other associations are not portable.

产生什么ON DELETE CASCDADE到 DDL，有供应商扩展 @OnDelete在 hibernate 中:

@OnDelete(action=OnDeleteAction.CASCADE)