@IndexColumn doesn't store the List index
-----------------------------------------

          Key: HHH-3425
          URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3425
        Project: Hibernate3
      Issue Type: Bug
      Components: core
  Affects Versions: 3.2.6
     Environment: Hibernate: 3.2.6.ga, hibernate-annotations-3.3.0.GA, MySQL: 5.0.51b-community-nt
       Reporter: J
       Priority: Minor


When you have a Parent class with a bidirectional one-to-many relation to a Child class (as a List), and the index column is mapped as a property in the associated entity, Hibernate will not store the index position of the List in the db. The value will stay 0 or null (depending whether you use int of Integer as index type).

Example taken directly from 2.4.6.2.3: http://www.hibernate.org/hib_docs/annotations/reference/en/html/entity.html#entity-hibspec-collection-extratype-indexbidir
With small change, for example "order" is changed to "position", because "order" is not allowed as columnname in MySQL.

------------ PARENT --------------
package entities;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Parent {
  // Properties
  @Id @GeneratedValue
  private Long id;

  @OneToMany(mappedBy="parent")
  @org.hibernate.annotations.IndexColumn(name="position")
  private List<Child> children = new ArrayList<Child>();

  private String name;

  // Getters & Setters
  public List<Child> getChildren() { return children; }
  public void setChildren(List<Child> children) { this.children = children; }
  public String getName() { return name; }
  public void setName(String name) { this.name = name; }

  public Parent() {}
}
------------------

----- CHILD -----
package entities;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import org.hibernate.Session;
import persistence.HibernateUtil;

@Entity
public class Child {
 // Properties
  @Id @GeneratedValue
  private Long id;

  @Column(name="position")
  private int position;

  @ManyToOne
  @JoinColumn(name="parent_id", nullable=false)
  private Parent parent;
 
  private String name;

  // Getters & Setters
  public Parent getParent() { return parent; }
  public void setParent(Parent parent) { this.parent = parent; }
  public String getName() { return name; }
  public void setName(String name) { this.name = name; }

}
------------------------------------

------ TEST --------------
    Session session = HibernateUtil.getSessionFactory().getCurrentSession();
    session.beginTransaction();
   
    Parent parent = new Parent();

    Child child1 = new Child();
    parent.getChildren().add(child1);
    child1.setParent(parent);

    Child child2 = new Child();
    parent.getChildren().add(child2);
    child2.setParent(parent);
   
    session.save(parent);
    session.save(child1);
    session.save(child2);
   
    session.getTransaction().commit();
--------------------------

After running this, the DB will stay:
mysql> select * from child;
+----+------+----------+-----------+
| id | name | position | parent_id |
+----+------+----------+-----------+
| 1 | NULL |   NULL |      1 |
| 2 | NULL |   NULL |      1 |
+----+------+----------+-----------+

instead of:
mysql> select * from child;
+----+------+----------+-----------+
| id | name | position | parent_id |
+----+------+----------+-----------+
| 1 | NULL |     1 |      1 |
| 2 | NULL |     2 |      1 |
+----+------+----------+-----------+


See also:
http://forum.hibernate.org/viewtopic.php?p=2392563

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