JPA/Hibernate/SpringBoot：插入@OneToMany 关系实体

Question

我正在努力在 JPA-Hibernate 设置中插入 @OneToMany 实体。

有两个关联的表，其中一个表的外键作为源表的主键。

employee

- id (PK)

employee_location

- employee_id (FK to employee)

这是我的实体：

Employee

@Entity(name = "employee")
class Employee {
     
     @Id
     @Column(name = "id")
     @GeneratedValue()
     private Long id;

     @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
     @JoinColumn(name = "employee_id", referencedColumnName = "id")
     private List<EmployeeLocation> employeeLocations;

} 

Employee Location

@Entity(name = "employee_location")
class EmployeeLocation {
     
         @Id
         @Column(name = "employee_id")
         private Long employeeId;

         @ManyToOne(cascade = CascadeType.ALL)
         @JoinColumn(name = "employee_id", referencedColumnName = "id", insertable = false, updatable = false)
         private Employee employee;

} 

保存实体：

List<EmployeeLocation> locations = Arrays.asList(new EmployeeLocation(), new EmployeeLocation()); 

Employee employee = new Employee();
employee.setLocations(locations);

employee.save(); // Throws exceptions

这引发了我这个错误： org.springframework.orm.jpa.JpaSystemException: ids for this class must be manually assigned before calling save():

我尝试将@Entity 更改为@Embeddable 并删除EmployeeLocation 上的@Id，但它给了我其他Unmapped entity 例外。

如何处理插入/更新@OneToMany 实体？这可能吗？

Answer 1

如何处理插入/更新 @OneToMany 实体？这可能吗？

如果您希望 DB 为您生成 primary key 值，您需要使用 @GeneratedValue 注释来请求它

@Entity(name = "employee")
class Employee {
     
     @Id
     @Column(name = "id")
     @GeneratedValue // mean -> "Hey, DB, give me an ID"!
     private Long id;

同样适用于EmployeeLocation

更多详情可以查看here

如果这不能完全解决您的问题，请发表评论。

Answer 2

在您的EmployeeLocation 实体（详细信息）中，您不能将主主键作为主键，它需要自己的主键。如下：

@Entity(name = "employee_location")
class EmployeeLocation {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "employee_location_id")
  private Integer id;

  @ManyToOne(cascade = CascadeType.ALL)
  @JoinColumn(name = "employee_id", referencedColumnName = "id", insertable = false, updatable = false)
  private Employee employee;

} 

Answer 3

如果 Employee 实体与 EmployeeLocation 实体具有 OneToOne 关系，您可以只使用 @MapsId。这样，EmployeeLocation id 属性就填充了帖子关联的标识符。

class EmployeeLocation {
     
    @Id
    @Column(name = "id")
    private Long id;

    @OneToOne
    @MapsId
    private Employee employee;
} 

但由于您的 Employee 实体与 EmployeeLocation 具有 OneToMany 关系，因此 Employee id 属性值不能用作 EmployeeLocation id 属性值，因为与同一 Employee 实体关联的两个或多个 EmployeeLocation 实体将具有相同的 id 值。

你需要这样的东西：

@Entity
public class EmployeeLocation {    

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    ...
    @ManyToOne Employee employee;
}

在这两种情况下，您都需要将 EmployeeLocation 实体绑定到 Employee 实体，例如：

class Employee {
    ....
    public void addLocation(EmployeeLocation location) {
        location.setEmployee(this);
        this.employeeLocations.add(location);
    }

    public void setLocations(List<EmployeeLocation> locations) {
        for (EmployeeLocation location : locations) {
            location.setEmployee(this);         
        }
        this.employeeLocations = locations;
    }
    ....
}

另一个选项：使用 ElementCollection

@Entity(name = "employee")
class Employee {
   
    @Id
    @Column(name = "id")
    @GeneratedValue
    private Long id;

    @ElementCollection
    @CollectionTable(
        name="employee_location",
        joinColumns=@JoinColumn(name="EMPLOYEE_ID"))    
    private Set<EmployeeLocation> employeeLocations;
}

@Embeddable
class EmployeeLocation {

    // properties
}