HIbernate overwrite data when persist/save entity

Question

I am new in Hibernate.when i save particular entity then it rewrite data from existing one.

I have used ID as auto generated as below:

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="id")
private int id;

Here i save Entity as below:

class StudDAO() {

public static void main(String[] args){
     StudDAO obj = new StudDAO();
     Stud stud = new Stud();
     stud.setName("Test");
     stud.setCity("Mumbai");
     obj.createStud(stud);
}

public void createStud(Stud stud) {
  try {

    Session session = HibernateSessionFactory.getSessionFactory().openSession();
    Transaction transaction = session.beginTransaction();
    session.save(stud);
    transaction.commit();

    } catch (Exception e) {
      // TODO: handle exception
       e.printStackTrace();
       transaction.rollback();
    }
}

}

if i will change entity value next time then it should generate next id rather than starting form 1st id.

any time result would be same like

mysql> select * from stud;

+----+--------+------+
| id | city   | name |
+----+--------+------+
|  1 | Mumbai | Test |
+----+--------+------+

1 row in set (0.00 sec)

what i want is in result like below:

mysql> select * from stud;
+----+--------+------+
| id | city   | name |
+----+--------+------+
|  1 | Mumbai | Test |
|  2 | Mumbai | Test |
+----+--------+------+
2 rows in set (0.00 sec)

Please help me for same..

Answer 1

If you are wanting to do an update rather than adding a new row to the database each time then you need to retrieve the desired entity, make any desired updates, and then save the entity again.

Answer 2

Try using saveOrUpdate(..)

Note that JPA (Hibernate) entities are identified by their @Id. If your object has the same id as the one in the db, an update will occur. Otherwise, logically, insert will happen.