[FIXED] Hibernate OneToOne relationship needs child value to be passed from parent domain object

Issue

I have created the below OneToOne relationship with Hibernate and Kotlin. However, when I am Initializing Parent() it requires me to set child value as Parent(child=null) which is not desired. Only initializing child should require parent as Child(parent=Parent(...) and if I add both parent to child and child to parent, it creates an infinite loop. What it the right way to avoid that?

    @Entity
    class Parent(
        @Id
        @Column(nullable = false, updatable = false, columnDefinition = "uuid")
        val id: UUID = UUID.randomUUID(),
        @OneToOne(cascade = [CascadeType.ALL], mappedBy = "parent")
        @JsonIgnore
        @JoinColumn(name = "child_id", referencedColumnName = "id")
        val child: Child?
    )
    @Entity
    class Subscriber(
        @Id
        @Column(nullable = false, updatable = false, columnDefinition = "uuid")
        val id: UUID = UUID.randomUUID(),
        @OneToOne(cascade = [CascadeType.ALL], optional = false)
        @JoinColumn(name = "id", columnDefinition = "uuid")
        @MapsId
        val parent: Parent
    )

Solution

As parent and child are mapped one to one and you want to use @MapsId to not create another extra PK in child table. Now Child object will use parent_id has its own PK.

For Parent

    @Entity
public class Parent {
    @Id
    @Column(nullable = false, updatable = false, columnDefinition = "uuid")
    private UUID id = UUID.randomUUID();

    public UUID getId() {
        return id;
    }

    public Parent setId(UUID id) {
        this.id = id;
        return this;
    }
}

Child

@Entity
public class Child {
    @Id
    @Column(nullable = false, updatable = false, columnDefinition = "uuid")
    private UUID id = UUID.randomUUID();

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    private Parent parent;

    public UUID getId() {
        return id;
    }

    public Child setId(UUID id) {
        this.id = id;
        return this;
    }

    public Parent getParent() {
        return parent;
    }

    public Child setParent(Parent parent) {
        this.parent = parent;
        return this;
    }
}

Check below screenshot for how table will look in database.

Answered By - Sagar Rout
Answer Checked By - David Marino (JavaFixing Volunteer)