如何在Hibernate继承关系中为子类PoliceMan设置独立主键police_id？

我定义了Person父类：

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "PERSON")
public class Person {
    @Id
    @Column(name = "person_id")
    @SequenceGenerator(sequenceName = "PERSON_ID_SEQ", allocationSize = 1, name="PERSON_ID_SEQ")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "PERSON_ID_SEQ")
    private Long personId;
    
    private String name;
}

以及继承自Person的PoliceMan子类：

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "POLICE_MAN")
public class PoliceMan extends Person{
    @Id
    @Column(name = "police_id")
    private Long policeId;
    
    private String something;
}

问题：父类Person已使用@Id注解，子类PoliceMan无法再用@Id将police_id设为独立唯一标识，该如何解决？

已参考过Hibernate继承相关内容，但仍未解决问题。

根据你的需求，分两种场景给出具体解决方式：

场景1：保留继承关系，子类主键关联父类主键 #

这种场景下，子类PoliceMan作为特殊的Person实例，使用JOINED继承策略，子类表的主键同时作为关联父类表的外键：

1. 修改父类Person，指定继承策略

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "PERSON")
@Inheritance(strategy = InheritanceType.JOINED)
public class Person {
    @Id
    @Column(name = "person_id")
    @SequenceGenerator(sequenceName = "PERSON_ID_SEQ", allocationSize = 1, name="PERSON_ID_SEQ")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "PERSON_ID_SEQ")
    private Long personId;
    
    private String name;
}

2. 调整子类PoliceMan的主键映射

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "POLICE_MAN")
@PrimaryKeyJoinColumn(name = "police_id", referencedColumnName = "person_id")
public class PoliceMan extends Person{
    // 移除子类的@Id注解，police_id会同时作为子类主键和关联父类的外键
    private String something;
}

场景2：仅复用父类属性，子类完全独立拥有主键 #

如果你的核心需求只是复用Person的属性，不需要将PoliceMan视为Person的实体子类，可将父类改为映射超类：

1. 修改父类为非实体的映射超类

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@MappedSuperclass
public class Person {
    // 移除@Id、@Entity等实体相关注解，仅保留属性映射
    private String name;
}

2. 子类定义独立主键

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "POLICE_MAN")
public class PoliceMan extends Person{
    @Id
    @Column(name = "police_id")
    // 可根据需求添加主键生成策略，比如@GeneratedValue
    private Long policeId;
    
    private String something;
}

额外说明 #

如果坚持要让police_id和person_id完全独立且保留继承关系，这种设计不符合ORM继承的语义（继承代表"is-a"关系，子类实例本质是父类实例的扩展），建议放弃继承，改为用@OneToOne或@ManyToOne关联Person类，实现两者独立主键的关联。

内容的提问来源于stack exchange，提问作者Amentos