Re: OJB and EJB best practices

[Armin Waibel <ar...@apache.org>]

Hi,

Juerg_Staub@rcomext.com wrote:

> I have some general questions concerning the usage of OJB (odmg) inside
> stateless session beans:
> 
> How many databases should I create. The examples session bean contains one
> db instance per bean. Can I share one db instance (OJBJ2EE_2.getInstance
> ().newDabase()) across multiple EJBs?
> 

yep, but each Implementation instance could only manage one Database at 
same time. When using multiple DB at same time you should use one 
Implementation/Database instance per database, e.g. bind to JNDI and 
lookup via


> We are facing problems whan rolling back transactions. Even when I call
> setRollbackOnly on the session context, some entries do still make it into
> the database. This is pretty wierd.
> 

I have same problems when using JBoss (seems that the 
Synchronization#afterCompletion will not be called, OJB use this method 
to sync cache and reset PB).
Please try to throw an EJBException instead (fix problem with JBoss).


> Another problem is that when I want to store a new object tree into the db
> and need to query for the exsiting tree on the db (via newOQLQuery()), I am
> not able to store my new tree anymore. I do a tx.lock(newTree,
> Transaction.WRITE), but when turning on tracing I see in the SQL that OBJ
> stores the tree I fetched from the DB.
> 

Could you explain more detailed, pseudo code?


regards,
Armin


> 
> Our environment is Websphere V5,  DB2, obj-1.0.rc6
> 
> Thanks
> 
> Jürg
> 
> 
> 
> 
> 
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Re: OJB and EJB best practices

[Juerg Staub <Ju...@rcomext.com>]

Armin,

> Could you explain more detailed, pseudo code?

public void storeOption(Option newOption) {

    OQLQuery query = this.odmg.newOQLQuery();
    Option currentOption = null;
    // Query current option for comparison
    try {
	query.create("select object from " + option.class.getName() + " where  
id=" + newOption.getId().intValue());
        currentOption = (Option)((List) query.execute()).get(0);
    }
    


    NarrowTransaction narrowTx = (NarrowTransaction) 
this.odmg.currentTransaction();

    // This code makes the currentOption persistent and not the newOption
    tx.lock(newOption, Transaction.WRITE);
    ((TransactionExt) tx).markDirty(o);
}

I verified the SQL statements and I see that really the currentOption is 
stored back into the database!

Furthermore we do sporadically get quite many LockNotGrantedExceptions when 
doing the tx.lock. I have no explanation why. How can I find out?

Thanks a lot

Juerg







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