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h.b.
 Post subject: Invalid session.getTransaction()?
PostPosted: Mon Oct 10, 2005 10:05 am 
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Joined: Wed Apr 13, 2005 10:34 am
Posts: 38
Hibernate version: 3.1rc1

Full stack trace of any exception that occurs:
Code:
org.hibernate.HibernateException: only beginTransaction() is valid when transaction not yet started
   at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:263)
   at $Proxy4.getTransaction(Unknown Source)
   ...


Why is it invalid to call session.getTransaction() before executing beginTransaction()?
It would be much more useful if getTransaction() returns null, if there is no current transaction.
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christian
 Post subject:
PostPosted: Mon Oct 10, 2005 10:48 am 
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Joined: Mon Aug 25, 2003 9:11 pm
Posts: 4592
Location: Switzerland
Why would that be easier? You call beginTransaction() to get a Transaction object and start a transaction at the same time. It does not make much sense to return null or return a Transaction object that isn't already active. The latter might have some uses, we are discussing the asymetry in the API right now. However, "null" is not an option.
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h.b.
 Post subject:
PostPosted: Mon Oct 10, 2005 11:33 am 
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I didnt't write "easier" but "more useful".

I've implemented a method-interceptor-based transaction management, where i'd like to know, if the current Session already has an active transaction.

My current implementation uses a ThreadLocal to store the transaction instance (just like the session), but it would be nice if session.getTransaction always returns something useful. Getting an "inactive" Transaction instance instead of null would be equivalent.

Thanks for your quick answer,

heiko
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steve
 Post subject:
PostPosted: Mon Oct 10, 2005 11:42 am 
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The reason it cannot is Serialization of the Session. Transactions, rightfully so, are not serializable. Thus serializing a session with a reference to a transaction will not work.

If you already have a method interceptor approach, what you'd probably want to do instead is to not use the standard ThreadLocalSessionContext, but to implement a custom version. In this custom one, build and bind the sessions from your existing interceptor code.
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h.b.
 Post subject:
PostPosted: Mon Oct 10, 2005 12:19 pm 
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Joined: Wed Apr 13, 2005 10:34 am
Posts: 38
Quote:
The reason it cannot is Serialization of the Session. Transactions, rightfully so, are not serializable. Thus serializing a session with a reference to a transaction will not work.

I'm not sure, I understand you correctly, but I don't need to serialize sessions. My app is a J2SE fat client. No appservers or rmi involved.

So what exactly is the use of the session.getTransaction method?

Quote:
If you already have a method interceptor approach, what you'd probably want to do instead is to not use the standard ThreadLocalSessionContext, but to implement a custom version. In this custom one, build and bind the sessions from your existing interceptor code.

Then I can't see any advantage compared to the classic HibernateUtil implementation (plus Transaction-ThreadLocal) I'm using right now.
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steve
 Post subject:
PostPosted: Mon Oct 10, 2005 2:19 pm 
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Did not say *you* needed to serialize sessions. A session is Serializable by contract; whether *you* serialize it or not, it needs to have the capability of being serialized while not connected.

Well, the only real advantage is swap-ability of implementations. When/if you switch over to JTA, it is a simple change of a few config properties in Hibernate versus changes in your code. If that is not an advantage for you, then hey don't use it. Simple, right?
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h.b.
 Post subject:
PostPosted: Mon Oct 10, 2005 4:24 pm 
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Ok, got it.

But then I don't see any additional value in this method, when all it does is returning the transaction instance that was already returned by beginTransaction (except for some stylish method chaining).

But hey, I don't have to use it, right? ;-)

Regards,

heiko
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steve
 Post subject:
PostPosted: Mon Oct 10, 2005 4:38 pm 
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exactly ;) Personally, I don't see the value of JTA-less transactions; but thats just me...

BTW, if you look at the source for that class, you'll see my comment about making that generated proxy less restrictive. Eventually, there will be a way to determine if there is an existing transaction. Right now other methods are throttled (like isOpen() for example) which also make alot of sense being available here.

http://cvs.sourceforge.net/viewcvs.py/hibernate/Hibernate3/src/org/hibernate/context/ThreadLocalSessionContext.java?rev=1.4&view=auto
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h.b.
 Post subject:
PostPosted: Mon Oct 10, 2005 5:39 pm 
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Joined: Wed Apr 13, 2005 10:34 am
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Quote:
Personally, I don't see the value of JTA-less transactions; but thats just me...

You're right, but unfortunately it is my client's requirement not to use an appserver. I was looking for a standalone TransactionManager and tried jotm/xapool, but had several problems with reliability (closed connections in the pool & crashing cleanup-threads). I refrained from trying out Tyrex because I only read unfavorable comments about it.

Please feel free to suggest an alternative.

Thanks.
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snpesnpe
 Post subject:
PostPosted: Mon Oct 10, 2005 7:12 pm 
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Joined: Sat Jun 12, 2004 4:49 pm
Posts: 915
try this

Code:
public Trransaction getTransaction(Session session) {
  Transaction transaction = null;
  try {
     transaction = session.getTransaction();
   } catch(HibernateException e) {
     return null;
    }
    return transaction;
}
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h.b.
 Post subject:
PostPosted: Tue Oct 11, 2005 6:50 am 
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Joined: Wed Apr 13, 2005 10:34 am
Posts: 38
Sure, that's a trivial solution, but I don't like using a per definition unrecoverable exception as a workaround. As long as there's no elegant way determining the existence of a running transaction, I'll stick with my current solution (tracking the transaction state inside HibernateUtil).

:)
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christian
 Post subject:
PostPosted: Tue Oct 11, 2005 7:24 am 
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Posts: 4592
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What would you do if you could "determine the existence of a running transaction"? Not start one? That's what beginTransaction() does internally.
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steve
 Post subject:
PostPosted: Tue Oct 11, 2005 7:24 am 
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Joined: Tue Aug 26, 2003 3:00 pm
Posts: 1816
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BTW, I just checked in some changes to allow the call to getTransaction() from one of these proxied Sessions:

Code:
            if ( !realSession.getTransaction().isActive() ) {
               // limit the methods available if no transaction is active
               if ( "beginTransaction".equals( method.getName() )
                     || "getTransaction".equals( method.getName() )
                     || "isTransactionInProgress".equals( method.getName() )
                     || "isOpen".equals( method.getName() ) ) {
                  log.trace( "allowing method [" + method.getName() + "] is non-transacted context" );
               }
               else {
                  throw new HibernateException( method.getName() + " is not valid without active transaction" );
               }
            }
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h.b.
 Post subject:
PostPosted: Tue Oct 11, 2005 7:49 am 
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Joined: Wed Apr 13, 2005 10:34 am
Posts: 38
christian wrote:
What would you do if you could "determine the existence of a running transaction"? Not start one? That's what beginTransaction() does internally.


I would throw a TransactionNotSupportedException if the called method is declared with TransactionAttributeType.NEVER.
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h.b.
 Post subject:
PostPosted: Tue Oct 11, 2005 7:55 am 
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Joined: Wed Apr 13, 2005 10:34 am
Posts: 38
steve wrote:
BTW, I just checked in some changes to allow the call to getTransaction() from one of these proxied Sessions:


Thanks!
:)
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