如何在JPA Entity中定义由两个@OneToOne字段组成的复合主键

实现方案 #

你提出的需求可以实现，之前使用@PrimaryKeyJoinColumn失败是因为该注解主要用于单主键的派生主键场景，复合主键场景需要配合@IdClass或@EmbeddedId方案实现，以下是两种可行的实现方式：

方案一：@IdClass 实现（更贴合你的使用习惯） #

该方案可以直接将@OneToOne关联字段作为主键的组成部分，结构更直观。

1. 首先定义复合主键类

import java.io.Serializable;
import java.util.Objects;

// 复合主键类必须满足三个要求：实现Serializable、重写equals和hashCode、存在无参构造
public class EmployeeId implements Serializable {
    // 字段名必须和EmployeeEntity中标注@Id的关联字段名完全一致
    private PersonEntity person;
    private DepartmentEntity department;

    public EmployeeId() {}

    public EmployeeId(PersonEntity person, DepartmentEntity department) {
        this.person = person;
        this.department = department;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        EmployeeId that = (EmployeeId) o;
        return Objects.equals(person, that.person) && Objects.equals(department, that.department);
    }

    @Override
    public int hashCode() {
        return Objects.hash(person, department);
    }
}

2. 调整EmployeeEntity实体配置

import javax.persistence.*;

@Entity
@Table(name = "EMPLOYEE")
@IdClass(EmployeeId.class) // 绑定复合主键类
public class EmployeeEntity {

    @Id
    @OneToOne
    @JoinColumn(name = "PERSON_ID", referencedColumnName = "ID", nullable = false)
    private PersonEntity person;

    @Id
    @OneToOne
    @JoinColumn(name = "DEPARTMENT_ID", referencedColumnName = "ID", nullable = false)
    private DepartmentEntity department;

    // 其他业务字段、getter、setter方法
}

该方案自动生成的表结构和你期望的完全一致，两个字段共同作为主键，同时分别为关联PERSON、DEPARTMENT表的外键。

方案二：@EmbeddedId 实现 #

该方案将主键字段和关联字段分离，适合主键包含非关联字段的场景。

1. 定义嵌入式主键类

import javax.persistence.Embeddable;
import java.io.Serializable;
import java.util.Objects;

@Embeddable
public class EmployeeId implements Serializable {
    @Column(name = "PERSON_ID", nullable = false)
    private Long personId;
    @Column(name = "DEPARTMENT_ID", nullable = false)
    private Long departmentId;

    public EmployeeId() {}

    public EmployeeId(Long personId, Long departmentId) {
        this.personId = personId;
        this.departmentId = departmentId;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        EmployeeId that = (EmployeeId) o;
        return Objects.equals(personId, that.personId) && Objects.equals(departmentId, that.departmentId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(personId, departmentId);
    }
}

2. 调整EmployeeEntity实体配置

import javax.persistence.*;

@Entity
@Table(name = "EMPLOYEE")
public class EmployeeEntity {

    @EmbeddedId
    private EmployeeId id;

    @OneToOne
    @MapsId("personId") // 关联主键类中的personId字段
    @JoinColumn(name = "PERSON_ID", insertable = false, updatable = false)
    private PersonEntity person;

    @OneToOne
    @MapsId("departmentId") // 关联主键类中的departmentId字段
    @JoinColumn(name = "DEPARTMENT_ID", insertable = false, updatable = false)
    private DepartmentEntity department;

    // 其他业务字段、getter、setter方法
}

注意事项 #

• 保存EmployeeEntity前必须先保存PersonEntity和DepartmentEntity，保证关联对象处于持久化状态
• 若使用Spring Data JPA，Repository接口的主键泛型需要替换为对应的复合主键类，示例：public interface EmployeeRepository extends JpaRepository<EmployeeEntity, EmployeeId>

内容的提问来源于stack exchange，提问作者Oleg Leinov