can someone please explain me @MapsId in hibernate?

Question

Can someone please explain to me @MapsId in hibernate? I\'m having a hard time understanding it.

It would be great if one could explain it with an examp

Answer 1

I found this note also useful: @MapsId in hibernate annotation maps a column with another table's column.

It can be used also to share the same primary key between 2 tables.

Example:

@Entity
@Table(name = "TRANSACTION_CANCEL")
public class CancelledTransaction {
    @Id
    private Long id; // the value in this pk will be the same as the
                     // transaction line from transaction table to which 
                     // this cancelled transaction is related

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ID_TRANSACTION", nullable = false)
    @MapsId
    private Transaction transaction;
    ....
}

@Entity
@Table(name = "TRANSACTION")
@SequenceGenerator(name = "SQ_TRAN_ID", sequenceName = "SQ_TRAN_ID")
public class Transaction  {
    @Id
    @GeneratedValue(generator = "SQ_TRAN_ID", strategy = GenerationType.SEQUENCE)
    @Column(name = "ID_TRANSACTION", nullable = false)
    private Long id;
    ...
}