如何在JPA中创建和处理复合主键

Question

实体应该是什么样子的？我如何用另一个版本复制它？

id Version ColumnA

1   0      Some data
1   1      Some Other data
2   0      Data 2. Entry
2   1      Data

Answer 1

您可以创建一个包含两个键的嵌入类,然后在实体中以embeddedId的形式引用该类。

您需要@embeddedid和@embeddable注释。

@Entity
public class YourEntity {
    @EmbeddedId
    private MyKey myKey;

    @Column(name = "ColumnA")
    private String columnA;

    /** Your getters and setters **/
}

@Embeddable
public class MyKey implements Serializable {

    @Column(name = "Id", nullable = false)
    private int id;

    @Column(name = "Version", nullable = false)
    private int version;

    /** getters and setters **/
}

实现此任务的另一种方法是使用@idclass注释，并将您的ID都放在该idclass中。现在，您可以在这两个属性上使用普通的@id注释

@Entity
@IdClass(MyKey.class)
public class YourEntity {
   @Id
   private int id;
   @Id
   private int version;

}

public class MyKey implements Serializable {
   private int id;
   private int version;
}