JPA/Hibernate：如何在同一会话中为具有 @Id 注释的字段保留重复值？

Question

客户说子表中不需要主键。所以 Child 表有两列“ID”和“Value”，其中 ID 可以重复。

当我删除 @Id 然后休眠说“没有为实体指定标识符”

当我在代码中保留@Id 时，hibernate 会说“javax.persistence.EntityExistsException：具有相同标识符值的不同对象已与会话相关联”；在坚持的同时

所以关键是我需要保留@Id，但是如何使用@Id 注释在一个会话中保留两个相同的 ID。

以下是代码：

主要实体：

public class CustomerAgreement implements Serializable {

    @OneToMany(mappedBy = "customerAgreement", orphanRemoval = true, fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST})
    private List<CustomerAgreementComputerAttachments> autoAttachComputersFromOrganizations;

组合实体：

public class CustomerAgreementComputerAttachments implements Serializable{

    private static final long serialVersionUID = 1L;
    @Id
    @ManyToOne
    @JoinColumn(name = "ID")
    private CustomerAgreement customerAgreement;

主程序：

  public static List<CustomerAgreement> create() {
        List<CustomerAgreement> li = new ArrayList<CustomerAgreement>();
        CustomerAgreement cAgreement = new CustomerAgreement();
        cAgreement.setId(2222l);
        cAgreement.setName("Tillu");;
        cAgreement.setCustomerId("140");


        List<CustomerAgreementComputerAttachments> catl = new ArrayList<>();
        CustomerAgreementComputerAttachments catt = new CustomerAgreementComputerAttachments();
        catt.setAttachmentValue("TEST");
        catt.setCustomerAgreement(cAgreement);
        CustomerAgreementComputerAttachments tatt = new CustomerAgreementComputerAttachments();
        tatt.setAttachmentValue("TESTy");
        tatt.setCustomerAgreement(cAgreement);
        catl.add(catt);
        catl.add(tatt);
        cAgreement.setAutoAttachComputersFromOrganizations(catl);



        li.add(cAgreement);
        return li;
    }
    public static void main(String[] args) {

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("IntegratorMasterdataPU");
        em = emf.createEntityManager();
        em.getTransaction().begin();
        for(CustomerAgreement ca: create()) {

            em.persist(ca);

        }
        em.getTransaction().commit();

    }

Answer 1

实体必须可以通过唯一键来识别。这不需要对应于任何数据库主键，但必须有一个或多个唯一列可用于标识实体。

如果这不可能，那么您需要将CustomerAgreementComputerAttachment 设为@Embeddable。

与实体不同，@Embeddable 没有独立身份（没有@ID）。在此处进一步查看：

What is difference between @Entity and @embeddable

@Entity
public class CustomerAgreement  {

    @ElementCollection
    @JoinTable(name="...", joinColumn = "id")
    private List<CustomerAgreementComputerAttachment> attachments;
}

和

@Embeddable
public class CustomerAgreementComputerAttachments {

    //No back reference to CustomerAgreement   
    //Other fields as required.
}