How to persist oneToOne relation when saving secondary Entity

user_5532928 0
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I'm using SPRING DATA JPA and I have following entities:

public class EntityA {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SOME_SEQ")
    @SequenceGenerator(sequenceName = "SOME_SEQ", allocationSize = 1, name = "SOME_SEQ")
    private Long id;

    private String name;
    
    @OneToOne(mappedBy = "entityBField", cascade = CascadeType.ALL)
    private EntityB entityB;
}
    
    
public class EntityB {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SOME_OTHER_SEQ")
    @SequenceGenerator(sequenceName = "SOME_OTHER_SEQ", allocationSize = 1, name = "SOME_OTHER_SEQ")
    private Long id;

    private Integer type;

    @OneToOne
    @JoinColumn(name = "entityaId", referencedColumnName = "id")
    private EntityA entityBField;
}

This is the tables definition:

create table EntityA(
  id int primary key,
  name varchar(255)
);
create table EntityB(
  id int primary key,
  type int,
  entitya_Id int  FOREIGN KEY ("entitya_Id")
      REFERENCES "EntityA" ("id")
);

I create and save one instance as follow:

    EntityA a = new EntityA();
    EntityB b = new EntityB();
    a.setEntityB(b);
    entityARepository.save(a)

What happens is that both entityA and entityB are persisted, but the foreign key entityaId on EntityB is null. Could you suggest how should I persist the foreign key linking EntityB to EntityA?

spring-data-jpa one-to-one persistence jpa
2 Answers

You need to implement method EntityA.setEntityB like this:

public class EntityA {

    public void setEntityB(EntityB entityB) {
        if (entityB == null) {
            if (this.entityB != null) {
                this.entityB.setEntityBField(null);
            }
        }
        else {
            entityB.setEntityBField(this);
        }
        this.entityB = entityB;
    }

}

EntityB.setEntityBField should be usual setter:

public class EntityB {

  public void setEntityBField(EntityA entityBField) {
    this.entityBField = entityBField;
  }

}

Also, you might need "optional = false" in the annotation:

@OneToOne(mappedBy = "entityBField", cascade = CascadeType.ALL, optional = false)
private EntityB entityB;

See the example in this article: https://vladmihalcea.com/the-best-way-to-map-a-onetoone-relationship-with-jpa-and-hibernate/

Note:

mappedBy = "entityBField" means that

EntityB.entityBField is responsible for managing one-to-one relationship,

so when you create EntityB b = new EntityB() and set a.setEntityB(b), then b.entityBField is null when you do cascading save: entityARepository.save(a)

This is why b.entityBField (foreign key "entitya_Id") is null in the database.

By implementing correct setter in EntityA, you help JPA understand, that entityB.entityBField should be set to the primary key of EntityA (entityB.setEntityBField(this))

user_126378390

The easiest solution would be like this:

EntityA a = new EntityA();
EntityB b = new EntityB();
b.setEntityBField(a);
entityARepository.save(a)

The only change you need to make is the following line:

b.setEntityBField(a);
user_126378390
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