Update just some columns

y0dA · **Joined:** Fri May 25, 2007 4:03 am **Posts:** 15

Hi!
I load just, for example 3 columns (a,b,c) from my table(A) - which also contains more columns like x,y,z.

now i wanna load just these 3 columns:

Code:

public static List<A> readBatchData() {
 Session session = HibernateUtil.getCurrentSession();
 Transaction tx = null;
 ArrayList<A> values = null;
 try {
       tx = session.beginTransaction();
       /* read special columns from db */
      values = (ArrayList<A>)session.createQuery   
        (select new A(a,b,c) from A).list();
      /* commit and close session */
      tx.commit();      
 } catch (Exception e) {
    if (tx != null) {
      tx.rollback();
    }
 } finally {      
   session = null;
   tx = null;
 }
  return values;
}

Then i update the data and then i wanna update these colums at the database table:

Code:

   public static void updateBatchData(final List<A> updateList) {
      Session session = HibernateUtil.getCurrentSession();
      Transaction tx = null;
      try {
         tx = session.beginTransaction();
         
         for (A model : updateList) {
            /* update */
            session.saveOrUpdate(model);
         }         
         tx.commit();   
      } catch (Exception e) {
         if (tx != null) {
            tx.rollback();
         }
      } finally {
         session = null;
         tx = null;
      }
   }

But if i do it like that, then the other columns (x,y,z) will be set NULL - any solutions?

Second question:
when

Code:

session.saveOrUpdate(model);

get called thats already a database interaction (columns get set at db?) or the model got saved at the hibernate session until

Code:

tx.commit()

get called?

best regards.

chucky · **Joined:** Mon Jun 12, 2006 5:33 am **Posts:** 63

Hi y0dA,
use the interface type List instead of ArrayList (hibernate has its own List implementation). And you don't need to cast when retrieving the result set.
Just :

Code:

List values = null;
....
values = session.createQuery   
        (select new A(a,b,c) from A).list(); 
...

chucky · **Joined:** Mon Jun 12, 2006 5:33 am **Posts:** 63

For the second question:
database synchronization happens only when you commit or call explicitly flush on the session

y0dA · **Joined:** Fri May 25, 2007 4:03 am **Posts:** 15

Hi!

chucky wrote:

Hi y0dA,
use the interface type List instead of ArrayList (hibernate has its own List implementation). And you don't need to cast when retrieving the result set.
Just :

Code:

List values = null;
....
values = session.createQuery   
        (select new A(a,b,c) from A).list(); 
...

Loading isnt the problem (but thanks for this), the problem is the update which override all other columns with null.

Quote:

For the second question:
database synchronization happens only when you commit or call explicitly flush on the session

So the model still stay at the session until i do a commit or flush?

best regards

piet.t · **Joined:** Fri May 12, 2006 4:05 am **Posts:** 106

As far as I understand your updateList contains newly created object instances that have only those values set that you want to be changed in the database.
Hibernate's default behaviour is to save all of the object's fields, since you might want to set the null-values in the database.
If you want only non-null-values to be updated in the database you'll have to set dynamic-update="true" in your class-mapping.