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1.简介

解决JPA/hibernate 实体多对多关系下，操作实体无法直接级联删除中间表，报错。

2.环境

1. jdk1.8
2. springboot:2.2.8.RELEASE

3.解决思路

1. 正常多对多

• 实体A使用多对多关联（@ManyToMany）关联B，JPA自动生成第三张中间表C，
• 然后在需要删除实体并且级联删除中间表时，提前删除中间表C的关联数据。

2. 双向一对多

• 实体A使用双向一对多（@OneToMany）关联C，并且设置C为维护方;
• 实体B使用双向一对多（@OneToMany）关联C，并且设置C为维护方;
• 通过JPA任意删除A/B都会删除中间表数据C，而不会删除另一方

4.代码

4.1 双向一对多实现

实体A

@Data
@Entity
@Table(name = "tb_a")
public class TbA {
    @Id
    @Column(name = "c_uuid", unique = true, length = 36, nullable = false)
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "org.hibernate.id.UUIDGenerator")
    private String uuid;
    
    @OneToMany(cascade = {CascadeType.ALL},mappedBy = "a")
    private List<TbC> cList;
}

实体B

@Data
@Entity
@Table(name = "tb_b")
public class TbB {
    @Id
    @Column(name = "c_uuid", unique = true, length = 36, nullable = false)
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "org.hibernate.id.UUIDGenerator")
    private String uuid;
    
    @OneToMany(cascade = {CascadeType.ALL},mappedBy = "b")
    private List<TbC> cList;
}

中间表C

@Data
@Entity
@Table(name = "tb_c")
@IdClass(TbC.TbCEmbeddable.class)
public class TbC {
    @Id
    @ManyToOne(cascade = {CascadeType.MERGE, CascadeType.REFRESH})
    @JoinColumn(name = "c_a_foreign_key")
    private TbA a;

    @Id
    @ManyToOne(cascade = {CascadeType.MERGE, CascadeType.REFRESH})
    @JoinColumn(name = "c_b_foreign_key")
    private TbA b;

    @Data
    public static class TbCEmbeddable implements Serializable {
        private TbA a;
        private TbB b;
    }
}

级联删除代码

@NoRepositoryBean
public interface BaseDao<T,ID extends Serializable> extends JpaRepository<T,ID> , JpaSpecificationExecutor<T> {
//RestResource
}

BaseDao<TbCollectManageItem,String> dao = factory.getDao(TbCollectManageItem.class);
        dao.deleteById(uuid);