@Entity
class Parent {
    @Id
    private int id;
 
    @OneToOne(cascade = CascadeType.ALL, mappedBy = "parent", orphanRemoval = true)
    private Child child;
 
    // getters and setters
}
 
@Entity
class Child {
    @Id
    private int id;
 
    private String data;
 
    @MapsId
    @OneToOne
    private Parent parent;
 
    // getters and setters
}