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1.簡介

解決JPA/hibernate 實體多對多關(guān)系下，操作實體無法直接級聯(lián)刪除中間表，報錯。

2.環(huán)境

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

3.解決思路

1. 正常多對多

• 實體A使用多對多關(guān)聯(lián)（@ManyToMany）關(guān)聯(lián)B，JPA自動生成第三張中間表C，
• 然后在需要刪除實體并且級聯(lián)刪除中間表時，提前刪除中間表C的關(guān)聯(lián)數(shù)據(jù)。

2. 雙向一對多

• 實體A使用雙向一對多（@OneToMany）關(guān)聯(lián)C，并且設(shè)置C為維護方;
• 實體B使用雙向一對多（@OneToMany）關(guān)聯(lián)C，并且設(shè)置C為維護方;
• 通過JPA任意刪除A/B都會刪除中間表數(shù)據(jù)C，而不會刪除另一方

4.代碼

4.1 雙向一對多實現(xiàn)

實體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;
}

實體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;
}

中間表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;
    }
}

級聯(lián)刪除代碼

@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);