EclipseLink/Examples/JPA/2.0/OrderColumns

How to maintain order in a List relationship using an OrderColumn

JPA 2.0 adds support for an OrderColumn. An OrderColumn can be used to define an order List on any collection mapping. It is defined through the @OrderColumn annotation or <order-column> XML element.

The OrderColumn is maintained by the mapping and should not be an attribute of the target object. The table for the OrderColumn depends on the mapping. For a OneToMany mapping it will be in the target object's table. For a ManyToMany mapping or a OneToMany using a JoinTable it will be in the join table. For an ElementCollection mapping it will be in the target table.

Example of a collection order column database

EMPLOYEE (table)

ID	FIRSTNAME	LASTNAME	SALARY
1	Bob	Way	50000
2	Sarah	Smith	60000

EMPLOYEE_PHONE (table)

EMPLOYEE_ID	PHONE_ID	INDEX
1	1	0
1	3	1
2	2	0
2	4	1

PHONE(table)

ID	AREACODE	NUMBER
1	613	792-7777
2	416	798-6666
3	613	792-9999
4	416	798-5555

Example of a collection order column annotation

@Entity
public class Employee {
  @Id
  private long id;
  ...
  @OneToMany
  @OrderColumn(name="INDEX")
  private List<Phone> phones;
  ...
}
 
@Entity
public class Phone {
  private int index = 0;
}

Example of a collection order column XML

<entity name="Employee" class="org.acme.Employee" access="FIELD">
    <attributes>
        <id name="id"/>
        <one-to-many name="phones">
            <order-column name="INDEX"/>
        </one-to-many>
    </attributes>
</entity>