OneToMany双向映射未保存其外键

Question

I have one-to-many relationship between Employee & Phone entities like this:

@Entity
public class Employee {
    @Id
    @Column(name = "EMP_ID")
    private long id;

    private String name;

    @OneToMany(mappedBy = "owner")
    private List<Phone> phones = new ArrayList<Phone>();
}

@Entity
public class Phone {
    @Id
    private long id;
    private String phoneNumber;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "OWNER_ID")
    private Employee owner;
}

In my code if I save phone first then employee next:

session.save(phone);
session.save(employee);

Then I am seeing and insert query to save Employee, then insert query to save Phone and then update query to update owner_id in Phone table.

So to avoid insert and update on Phone table, I have added below mapping in my Phone entity:

@Entity
public class Phone {
    ...
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "OWNER_ID", insertable=false, updatable=false)
    private Employee owner;
}

Now in this case, I see insert on Employee then insert on Phone, but the owner_id is null.

How to make sure that the owner_id is not null when I save the entities? I want to save Phone then Employee in my code not the other way.

Answer 1

As phone is a child entity, it will need reference of employee for saving. By annotating Phone with cascadeType, your phone will be saved with your employee entity. Your modified entities will be like this :

@Entity
public class Employee {
    @Id
    @Column(name = "EMP_ID")
    private long id;

    private String name;

    @OneToMany(mappedBy = "owner",cascade = CascadeType.ALL)
    private List<Phone> phones = new ArrayList<Phone>();

  /*getters and setters*/
}

@Entity
public class Phone {
    @Id
    private long id;
    private String phoneNumber;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "OWNER_ID", insertable=false, updatable=false,nullable=false)
    private Employee owner;
    /*getters and setters*/

}

And have to modify your saving logic as below :

Employee emp = new Employee();
private List<Phone> phones = new ArrayList<Phone>();
Phone phone = new Phone();
phone.setOwner(emp);

phones.add(phone);

emp.setPhones(phones);

session.save(emp);

Answer 2

According to your requirement, no need to use bidirectional. Try the following steps

1. Only need to declare @ManyToOne in Phone entity. So remove @OneToMany declaration from Employee entity.

2. Hibernate session.save(obj) returns the id of Object. So just save Phone first and catch id then save employee.See sample

     session.save(phone); long phoneOneId = phone.getId(); Phone phoneOne = new Phone(); phoneOne.setId(phoneOneId); // You can also add another phone like phoneTwo, phoneThree, ... List<Phone> phones = new ArrayList<Phone>(); phones.add(phoneOne); employee.setPhones(phones);