主键为外键的一对一映射-需要哪些注释 [英] One-to-one mapping where primary key is foreign key - what annotations are required

问题描述

我有下表:

Table: MyEntity {
    MyEntityId: primary-key, auto-generated
    // other fields ommited
}

Table: MyEntityLastAction {
    MyEntityId: primary-key
    // other fields ommited
}

• MyEntityLastAction.MyEntityId有一个约束，它必须存在于MyEntity中. (这是一个外键)
• MyEntityLastAction是一个非常大的记录，因此为什么将它拆分到另一个表中
• MyEntityLastAction.MyEntityId has a constraint that it must exist in MyEntity. (This is a foreign key)
• MyEntityLastAction is a VERY BIG record, hence why it is split out into another table

我无法正确设置实体注释.这大概是我的位置:

I am failing to setup the entity annotations correctly. Here is roughly where I am:

@Entity
public class MyEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public long myEntityId;
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
    public MyEntityLastAction lastAction;
}

@Entity
public class MyEntityLastAction {
    @Id
    public long myEntityId;
    @OneToOne(mappedBy = "MyEntity", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
    @JoinColumn(name = "MyEntityId")
    public MyEntity myEntity;
}

我尝试运行以下图像:

MyEntity myEntity = new MyEntity();
myEntity.lastAction = new MyEntityLastAction();

em.save(myEntity);

推荐答案

我认为您正在寻找@MapsId批注.这样可以使@OneToOne具有共享的主键.

I think you are looking for @MapsId annotation. This allows you to have @OneToOne with shared primary key.

请参见以下代码以供参考:

See the below code for reference:

@Entity
class MyEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public long myEntityId;
    @OneToOne(mappedBy = "myEntity", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
    public MyEntityLastAction lastAction;
}

@Entity
class MyEntityLastAction {
    @Id
    public long myEntityId;

    @OneToOne
    @JoinColumn(name="MyEntityId") 
    @MapsId     
    public MyEntity myEntity;
}

并保存实体:

        MyEntity me = new MyEntity();
        me.lastAction = new MyEntityLastAction();
        me.lastAction.myEntity = me;
        entityManager.persist(me);

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