Should I call "session.beginTransaction()" when I

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

Hi everyone:

I know if I save some data to database , I should use transaction like this:

Code:

Session session=HibernateUtil.currentSession();
Transaction t=session.beginTransaction();

User u=new User();
.....................
...............
session.save(u);
t.commit();
HibernateUtil.closeSession();

It means that I need have to use a transaction.

If I query database only, Should I use transaction?
For example:

Code:

Session session=HibernateUtil.currentSession();
Transaction t=session.beginTransaction();  // <----It is nessecery to
                                                              //begin
                                                           //transaction here?
List list=session.find("from User");
.....................
Broker b=(Broker)session.get(Broker.class,broker_id);
.....................

t.commit();
HibernateUtil.closeSession();

I think it should be changed to following:

Code:

Session session=HibernateUtil.currentSession();

List list=session.find("from User");
.....................
Broker b=(Broker)session.get(Broker.class,broker_id);
.....................

HibernateUtil.closeSession();

The later will be better I think. Is it correct? Thks!

anthony · **Posted:** Fri Oct 22, 2004 2:42 am

always use transaction no matter if you are reading, updating, inserting

curio · **Joined:** Tue Oct 05, 2004 9:45 am **Posts:** 263

@anthony
it might be a really silly question (maybe answered in the booked - it's ordered but has 14 days to delivery) ...
but why should i open a transaction when i really only want to read information? is there a short explanation for that?
Sorry for going hibernate-OT ... i thing that's something that should be done even if i'm not using hibernate ...

I believe yo, and will change that in my codings, but i would like to understand why ;)

thx!
curio

christian · **Posted:** Fri Oct 22, 2004 2:53 am

Short explanation: some database management systems need transaction demarcation for read operations, since they manage locks even for reading. Others don't, but you'd like to keep your code portable and clean (and frankly, there is no performance penaltity or other disadvantage, and your code is much easier to understand). So, you could ask this question as "Why do you think you _don't_ need it?

anthony · **Posted:** Fri Oct 22, 2004 2:55 am

oh, the best way is to ask google... or search the forum, this has been discussed many times

but you're right... you have to trust me ;)

curio · **Joined:** Tue Oct 05, 2004 9:45 am **Posts:** 263

@christian
That really sounds good to me ... and knowing that different databases do reading different makes it more clear ...
so i will change my coding ...

@anthony
sure, i trust you (in hibernate and db-questions :) ;) ) ... my knowledge about database-systems and or-layers are more than only far away from yours (and the rest of the hibernate team) .... and that's good ... don't want to think about what hibernate would be with my poor-db-knowledge ;) ... but i'm working on not asking silly questions in the forum ;) and filling my gaps ....

thx for explanation :)

gtx
curio

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

anthony wrote:

always use transaction no matter if you are reading, updating, inserting

Thks for your reply : )

But I found a problem: When I query database only,if I use transaction ,Tomcat will report warn:

Code:

15:56:48,781  WARN SessionImpl:3390 - afterTransactionCompletion() was never cal
led

I don't know why this happen. : (

Should I use

Code:

Transaction t=s.beginTransaction();

?

anthony · **Posted:** Fri Oct 22, 2004 6:45 am

read again some code example in the reference guide, looks like

1- get session
2- tx = session.beginTransaction
3- do job
4- tx.commit
5- session.close

in catch block: tx.rollback + session.close

curio · **Joined:** Tue Oct 05, 2004 9:45 am **Posts:** 263

i think one place where the 'afterTransactionCompletion'-method gets called is during a 'commit()'.
Silly question perhaps .. but do you 'commit' after reading?

gtx
curio

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

anthony wrote:

read again some code example in the reference guide, looks like

1- get session
2- tx = session.beginTransaction
3- do job
4- tx.commit
5- session.close

in catch block: tx.rollback + session.close

But the HibernateUtil's closeSession method will close current session.
This class is in the hibernate docs.

Code:

public class HibernateUtil {

    private static final SessionFactory sessionFactory;

    static {
        try {
            sessionFactory = new Configuration().configure().buildSessionFactory();
        } catch (HibernateException ex) {
            throw new RuntimeException("Exception building SessionFactory: " + ex.getMessage(), ex);
        }
    }

    public static final ThreadLocal session = new ThreadLocal();

    public static Session currentSession() throws HibernateException {
        Session s = (Session) session.get();
        // Open a new Session, if this Thread has none yet
        if (s == null) {
            s = sessionFactory.openSession();
            session.set(s);
        }
        return s;
    }

    public static void closeSession() throws HibernateException {
        Session s = (Session) session.get();
        session.set(null);
        if (s != null)
            s.close();
    }
}

Why session is not close some time after I invoke the HibernateUtil.closeSession() method? It is memory leak?

anthony · **Posted:** Fri Oct 22, 2004 1:49 pm

if you use hibernateUtil, forget session.close

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

anthony wrote:

if you use hibernateUtil, forget session.close

I think I should change the code to this:

Code:

try{
Session session=HibernateUtil.currentSession(); 
Transaction t=session.beginTransaction();  // <----It is nessecery to 
                                                              //begin 
                                                           //transaction here? 
List list=session.find("from User"); 
..................... 
Broker b=(Broker)session.get(Broker.class,broker_id); 
..................... 

}catch(...){
.............
}finally{
t.commit(); 
HibernateUtil.closeSession(); 
}

This maybe avoid the problem.

Myk · **Joined:** Sun Jan 04, 2004 2:46 pm **Posts:** 147

In short always use a transaction, there's negligible overhead and it can avoid problems that are hard to pin down later. Generally do tx.commit() at the end of your try block, tx.rollback() in your catch block and session.close() in your finally block.

Yashnoo · **Joined:** Wed Dec 17, 2003 4:24 am **Posts:** 188

Myk wrote:

In short always use a transaction, there's negligible overhead and it can avoid problems that are hard to pin down later. Generally do tx.commit() at the end of your try block, tx.rollback() in your catch block and session.close() in your finally block.

Thank you Myk!

The final code is this :

Code:

Session session=null;
Transaction t=null;
try{ 
    session=HibernateUtil.currentSession(); 
    t=session.beginTransaction();  
                                                                                                           
List list=session.find("from User"); 
..................... 
Broker b=(Broker)session.get(Broker.class,broker_id); 
..................... 
t.commit(); 
}catch(...){ 
session.rollback();
............. 
}finally{ 
try{
HibernateUtil.closeSession(); 
}catch(..){
............
}

} 

It will work no problem. : )