JPA映射不保留具有关系的实体

Question

For example, I have the following entities: Room entity:

@Entity
public class Room extends Base {

@OneToMany(mappedBy = "room")
private List<Person> persons;
//getters and setters
}

And the Person entity:

@Entity
public class Person extends Base {

@ManyToOne
private Room room;

private String name;
//getters and setters
}

If I add person to room's persons list and then persist, the room is added, but person is not. I thought, enough is to add mappedBy parameter to OneToMany annotation, but.. what should I do else?

Answer 1

You need to set CascadeType=PERSIST or ALL on @OneToMany . And Also set room variable in Person class to populate foreign key in Person table.

Answer 2

Do the opposite, set a Room as the room field of a Person instance:

Room room = ...;
person.setRoom(room);
// persist the person  

With the mappedBy , you specify that which entity owns the relationship . Updating the relationship between those two entities is the responsibility of the owning side .

In your example, the Person owns the relationship, so it's his responsibility to update the foreign key, not Room 's, so when you add a Person to list of persons in Room and update the Room , Room wouldn't update the foreign key for you.