如何在JPA中创建和处理复合主键 [英] How to create and handle composite primary key in JPA

问题描述

我想拥有来自同一数据条目的版本。换句话说，我想用另一个版本号复制该条目。

I want to have versions from the same data entry. In other words, I want to duplicate the entry with another version number.

id - Version 将是主要的键。

实体应该如何？如何与其他版本复制？

How should the entity look like? How can I duplicate it with another version?

id Version ColumnA

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

推荐答案

您可以创建一个嵌入式类，其中包含您的两个键，然后将该类引用为<$ 实体中的c $ c> EmbeddedId 。

You can make an Embedded class, which contains your two keys, and then have a reference to that class as EmbeddedId in your Entity.

您需要 @EmbeddedId 和 @Embeddable 注释。

You would need the @EmbeddedId and @Embeddable annotations.

@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，并放置 id 在 IdClass 中。现在你可以在两个属性上使用普通的 @Id 注释

---

Another way to achieve this task is to use @IdClass annotation, and place both your id in that IdClass. Now you can use normal @Id annotation on both the attributes

@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;
}

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