@Entity
@Table(name = "first_msg", uniqueConstraints = { @UniqueConstraint( columnNames = { "user_id", "login" } ) })
public class FirstMsgItem {
    @Id
    @SequenceGenerator(name="pk_sequence",sequenceName="firstmsg_id_seq", allocationSize=1)
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name = "id")
    private int id;
...