JPA 2.0-在父实体持久化时自动持久化子实体，给出org.hibernate.id.IdentifierGenera

Question

我有两个名为Customer和他的Biiling Address的实体。这种关系是一对一的。每个客户都有一个账单地址。我想在客户被持久化时自动持久化计费地址。客户id是customer实体的主键，也是地址实体中的主键和外键。

//parent table
public class CustomerDTO implements Serializable {
@Id
@GeneratedValue
@Column(name = "customer_id")
private Integer id;
@OneToOne(fetch=FetchType.LAZY,cascade=CascadeType.ALL )
@PrimaryKeyJoinColumn(name="customer_id")
BillingAddressDTO billingAddressDTO;

//child table
public class BillingAddressDTO implements Serializable {
@Id
@Column(name="customer_id")
private Integer id;

这是我用来持久化实体的代码

    customerDTO = new CustomerDTO();
    customerDTO.setFirstName(firstName);
    billingAddressDTO = new BillingAddressDTO();
    billingAddressDTO.setBillingAddress(address1);
    customerDTO.setBillingAddressDTO(billingAddressDTO);
   //persisting customer entity
   customerDAO.persist(customerDTO);

我得到以下异常

  Caused by: org.hibernate.id.IdentifierGenerationException: ids for this   
  class must be manually assigned before calling save():

我想给地址表分配相同的客户id，所以我不想手动分配。谢谢你抽出时间。

Answer 1

您需要的是所谓的派生标识符。在这种方法中，CustomerDTO（父实体）的主键与BillingAddressDTO（从属实体）共享。

@Entity
public class CustomerDTO implements Serializable {
    @Id
    @GeneratedValue
    @Column(name = "customer_id")
    private Integer id;
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn(name = "customer_id")
    private BillingAddressDTO billingAddressDTO;
    ...
}

@Entity
public class BillingAddressDTO implements Serializable {
    @Id
    private Integer id; // @Column is NOT allowed since id is indicated by @MapsId
    @MapsId
    @OneToOne(mappedBy = "billingAddressDTO")
    @JoinColumn(name = "customer_id")
    private CustomerDTO customerDTO;
    ...
}

在上述场景中，父实体CustomerDTO具有简单主键customer_id，并且从属实体BillingAddressDTO共享由关系属性customerDTO映射的单个主键属性。

---

更新：基于阿里评论的替代解决方案，避免双向关系

@Entity
public class CustomerDTO implements Serializable {
    @Id
    private Integer id;
    @MapsId
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "customer_id")
    private BillingAddressDTO billingAddressDTO;
    ...
}

@Entity
public class BillingAddressDTO implements Serializable {
    @Id
    @GeneratedValue
    @Column(name = "customer_id")
    private Integer id;
    ...
}

在上述场景中，父实体BillingAddressDTO具有简单主键customer_id，并且从属实体CustomerDTO共享由关系属性billingAddressDTO映射的单个主键属性。

---

从底层数据库的角度来看，实体将如下所示：

customer_id  firstname
-----------  ---------
          1  Ali Baba
customer_id  billingaddress
-----------  --------------
          1  my_address

参考文献：

• JPA 2.0规范，第2.4.1章：与派生标识相对应的主键