jpa - 保存辅助实体时如何保持 oneToOne 关系

Question

我正在使用 SPRING DATA JPA 并且我有以下实体:

public class EntityA {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SOME_SEQ")
    @SequenceGenerator(sequenceName = "SOME_SEQ", allocationSize = 1, name = "SOME_SEQ")
    private Long id;

    private String name;
    
    @OneToOne(mappedBy = "entityBField", cascade = CascadeType.ALL)
    private EntityB entityB;
}
    
    
public class EntityB {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SOME_OTHER_SEQ")
    @SequenceGenerator(sequenceName = "SOME_OTHER_SEQ", allocationSize = 1, name = "SOME_OTHER_SEQ")
    private Long id;

    private Integer type;

    @OneToOne
    @JoinColumn(name = "entityaId", referencedColumnName = "id")
    private EntityA entityBField;
}

这是表格定义:

create table EntityA(
  id int primary key,
  name varchar(255)
);
create table EntityB(
  id int primary key,
  type int,
  entitya_Id int  FOREIGN KEY ("entitya_Id")
      REFERENCES "EntityA" ("id")
);

我创建并保存一个实例如下:

    EntityA a = new EntityA();
    EntityB b = new EntityB();
    a.setEntityB(b);
    entityARepository.save(a)

发生的情况是 entityA 和 entityB 都被持久化了，但是 EntityB 上的外键 entityaId 为空。您能否建议我应该如何保留将 EntityB 链接到 EntityA 的外键？

Answer 1

您需要像这样实现方法 EntityA.setEntityB:

public class EntityA {

    public void setEntityB(EntityB entityB) {
        if (entityB == null) {
            if (this.entityB != null) {
                this.entityB.setEntityBField(null);
            }
        }
        else {
            entityB.setEntityBField(this);
        }
        this.entityB = entityB;
    }

}

EntityB.setEntityBField 应该是通常的 setter :

public class EntityB {

  public void setEntityBField(EntityA entityBField) {
    this.entityBField = entityBField;
  }

}

此外，您可能需要在注释中使用“optional = false”:

@OneToOne(mappedBy = "entityBField", cascade = CascadeType.ALL, optional = false)
private EntityB entityB;

参见本文中的例子: https://vladmihalcea.com/the-best-way-to-map-a-onetoone-relationship-with-jpa-and-hibernate/

注意:

mappedBy = "entityBField" 表示

EntityB.entityBField负责管理一对一关系，

因此，当您创建 EntityB b = new EntityB() 并设置 a.setEntityB(b) 时，b.entityBField 为 null当你进行级联保存时:entityARepository.save(a)

这就是为什么 b.entityBField(外键“entitya_Id”)在数据库中为空的原因。

通过在 EntityA 中实现正确的 setter，您可以帮助 JPA 理解 entityB.entityBField 应该设置为 EntityA 的主键 (entityB.setEntityBField(this))