Cannot swap two elements in a list

jgongo · **Joined:** Wed Oct 08, 2003 6:34 am **Posts:** 29

Hi there,

I would like to swap two elements in a list, but I'm not able to do it. Here is my code:

Code:

    Session hibernateSession = sessionFactory.openSession(  );
    Transaction transaction = hibernateSession.beginTransaction(  );

    try
      {
      String categoryId = httpServletRequest.getParameter( "categoryId" );
      Category category = (Category) hibernateSession.load( Category.class, categoryId );
      Publication publication = category.getPublication(  );

      int categoryIndex = publication.getCategories(  ).indexOf( category );
      if( categoryIndex > 0 )
        {
        Category swappedCategory = (Category) publication.getCategories(  ).remove( categoryIndex - 1 );
        publication.getCategories(  ).add( categoryIndex, swappedCategory );
        }

      hibernateSession.update( publication );
      transaction.commit(  );
      }
    finally
      {
      hibernateSession.close(  );
      }

Here is my mapping:

Code:

        <list name="categories" lazy="false" inverse="true"       cascade="all">
              <key column="publication"/>
              <index column="rank" type="integer" length="10"/>
              <one-to-many class="com.actaris.news.domain.Category"/>
        </list>
............
    <class name="com.actaris.news.domain.Category" table="category" dynamic-update="false" dynamic-insert="false">
        <many-to-one name="publication" class="com.actaris.news.domain.Publication" cascade="none" outer-join="auto" update="true" insert="true" column="publication" not-null="true" unique="false"/>

Am I doing anything stupid or what?

Regards
Jose

emmanuel · **Posted:** Thu Nov 27, 2003 5:54 pm

Hibernate does not support bidirectional relationship with indexed collection (such as list). The many-to-one is irrevelent.
Thus, you must set inverse="false" in the <list/>.

jgongo · **Joined:** Wed Oct 08, 2003 6:34 am **Posts:** 29

If I set inverse to false I get exceptions when deleting entities from the collection (foreign key not null). Should I set not-null to false in the foreign key and then set inverse to false?

Regards
Jose

jgongo · **Joined:** Wed Oct 08, 2003 6:34 am **Posts:** 29

Sorry, I'm new to hibernate and I think I haven't understood bidirectional associations.

What makes a bidirectional association? Do you have a bidirectional association when you have two entities that have a reference to each other? Or do you need to mark one end of the association with inverse="true" to consider this association bidirectional? What does imply a bidirectional association? Does one end of the association get updated automatically (the one with inverse="true") when the other end is changed?

Thanks in advance, regards
Jose

christian · **Posted:** Thu Nov 27, 2003 7:16 pm

Yes, an association where you can navigate from one entity to the other, starting on either side. In this case, you have to mark one end as inverse, see here for an explanation:

http://www.hibernate.org/Documentation/ ... nverseTrue

Hibernate supports only Sets or Bags for the "many" side of a one-to-many bidirectional association, not indexed collections like List or Array. A good start is the "Parent/Child Relationship" chapter in the reference documentation.

yehs220 · **Joined:** Thu Aug 28, 2003 8:41 pm **Posts:** 17

I think hibernate supports List for the "many" side of a one-to-many bidirectional association,you can maintain the index column in the "many" side(map the index column as a property of the "many" class),when you add a "many" object to an "one" object,set the index property of the "many" object manually.

emmanuel · **Posted:** Fri Nov 28, 2003 8:20 am

yehs220 wrote:

I think hibernate supports List for the "many" side of a one-to-many bidirectional association,you can maintain the index column in the "many" side(map the index column as a property of the "many" class),when you add a "many" object to an "one" object,set the index property of the "many" object manually.

Is that what you call a supported feature ?

yehs220 · **Joined:** Thu Aug 28, 2003 8:41 pm **Posts:** 17

At least it does work,and it is more efficient,it issues only one insert to add a "many" object.