Check out example codes for "hibernate onetone with mapsid". It will help you in understanding the concepts better.

Code Example 1

@Entity
public class VitalStats 
{
    @Id @Column(name="vitalstats_id") Long id;

    @MapsId 
    @OneToOne(mappedBy = "vitalStats")
    @JoinColumn(name = "vitalstats_id")   //same name as id @Column
    private Person person;

    private String stats;
}

Code Example 2

@Entity
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "person_id")
    private Long id;

    @OneToOne(cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn
    private VitalStats vitalStats;       
}

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