Kris,

Some more information: the NullPointerException from GetObjectCommand is thrown by the line:

        ((StatefulKnowledgeSessionImpl)ksession).session.getExecutionResult().getResults().put( this.outIdentifier,
                                                      object );

Method getExecutionResult() is returning null. Debugging my test case, I also notice that this.outIdentifier is also null.

I then had a look at the GetObjectsCommand class; in its execute method, there is a line similar to that above. However, it is contained within an if block that checks this.outIdentifier is not null:

        if ( this.outIdentifier != null ) {
           List objects = new ArrayList( col );
           
           ((StatefulKnowledgeSessionImpl)ksession).session.getExecutionResult().getResults().put( this.outIdentifier, objects );
       }
If something similar was done in GetObjectCommand, presumably this would fix my problem?

Hope this is of some use - regards,

Alan




Alan.Gairey@tessella.com
Sent by: rules-users-bounces@lists.jboss.org

29/10/2009 17:35
Please respond to
Rules Users List <rules-users@lists.jboss.org>
To
Kris Verlaenen <kris.verlaenen@cs.kuleuven.be>
cc
Rules Users List <rules-users@lists.jboss.org>
Subject
Re: [rules-users] [droolsflow] Code-based constraints for EventWait nodes - is this possible?






Kris,

Thanks - making the class SimpleFact serializable fixed that error.

However, I now have a new problem: I have a rule flow containing a work item - the handler attempts to update the SimpleFact instance in memory before completing the task. The code in the executeWorkItem method is as follows:

       Collection<FactHandle> factHandles = ksession.getFactHandles(new ObjectFilter() {
           public boolean accept(Object object) {
               return (object instanceof SimpleFact);
           }
       });
       for (Iterator<FactHandle> iterator = factHandles.iterator(); iterator.hasNext(); ) {
           FactHandle factHandle = iterator.next();
           SimpleFact fact = (SimpleFact) ksession.getObject(factHandle);
           fact.setStatus("Error");
           ksession.update(factHandle, fact);
       }

       workItemManager.completeWorkItem(workItem.getId(), null);

The call to getObject() causes the following exception to be thrown:

java.lang.NullPointerException
       at org.drools.command.runtime.rule.GetObjectCommand.execute(GetObjectCommand.java:35)
       at org.drools.persistence.session.SingleSessionCommandService.execute(SingleSessionCommandService.java:254)
       at org.drools.command.impl.CommandBasedStatefulKnowledgeSession.getObject(CommandBasedStatefulKnowledgeSession.java:369)
       at com.test.StatusChangeWorkItemHandler.executeWorkItem(StatusChangeWorkItemHandler.java:37)
       ...

I've attached another test case to illustrate the problem.



Once again, my sincere thanks for helping me with this.

Regards,

Alan



Kris Verlaenen <kris.verlaenen@cs.kuleuven.be>

29/10/2009 12:00


To
Alan.Gairey@tessella.com
cc
Rules Users List <rules-users@lists.jboss.org>
Subject
Re: [rules-users] [droolsflow] Code-based constraints for EventWait nodes - is this possible?







Alan,

The cause of the rollback of the transaction is this:
Caused by: java.io.NotSerializableException: com.test.SimpleFact

The reason is that, if you use persistence for your session, the
persister will try to save all runtime state of the engine.  This does
not only include process instances, but also rule-related state.  By
default, this also includes the data inserted in the memory.  We support
two strategies for storing this data: serialization of the data
(default) or JPA-based storage of entities (by reference).  In this
case, the persister is trying to serialize the test object you inserted
and fails.  Making it serializable should fix this.

Kris

Quoting Alan.Gairey@tessella.com:

> Kris,
>
> I've attached a simple test case (transaction manager, data source,
> etc.
> are configured via Spring). The error is thrown on line:
>
> ksession.insert(new SimpleFact());
>
> If this line is commented out, the rule flow executes without error.
>
>
>
> Many thanks for looking at this.
>
> Regards,
>
> Alan
>
>
>
>
> Kris Verlaenen <kris.verlaenen@cs.kuleuven.be>
> 28/10/2009 10:40
>
> To
> Alan.Gairey@tessella.com
> cc
> Rules Users List <rules-users@lists.jboss.org>
> Subject
> Re: [rules-users] [droolsflow] Code-based constraints for EventWait
> nodes
> - is this possible?
>
>
>
>
>
>
> Alan,
>
> Could you send me the entire output / stack trace (as the rollback
> of
> the transaction is usually caused by another exception)?
>
> Or a simple test case that shows the error, so I can take a look?
>
> Thx,
> Kris
>
> Quoting Alan.Gairey@tessella.com:
>
> > Kris,
> >
> > After posting my last question, I quickly came to the same
> conclusion
> > as
> > you, so I'm now using a rule-based constraint in my EventWait
> node.
> >
> > This however has presented a different problem. If I create my
> > session
> > from JPAKnowledgeService, then when I try to insert my fact into
> the
> >
> > session, I get the following error:
> >
> > bitronix.tm.internal.BitronixRollbackException: transaction was
> > marked as
> > rollback only and has been rolled back
> >         at
> >
> bitronix.tm.BitronixTransaction.commit(BitronixTransaction.java:153)
> >         at
> >
>
bitronix.tm.BitronixTransactionManager.commit(BitronixTransactionManager.java:96)
> >         at
> >
>
org.drools.persistence.session.SingleSessionCommandService.execute(SingleSessionCommandService.java:258)
> >         at
> >
>
org.drools.command.impl.CommandBasedStatefulKnowledgeSession.insert(CommandBasedStatefulKnowledgeSession.java:305)
> > (Everything works fine if I create my session from the knowledge
> base
> > -
> > i.e. with no state persistence.)
> > Prior to using a rule-based constraint (with no call to
> > CommandBasedStatefulKnowledgeSession.insert), the session created
> > from
> > JPAKnowledgeService worked OK.
> > I'm using the default JPA configuration from the Drools
> documentation
> >
> > (persisting to H2 database, etc.).
> > Any ideas what might be causing the problem?
> > Many thanks,
> > Alan
> >
> >
> >
> >
> > Kris Verlaenen <kris.verlaenen@cs.kuleuven.be>
> > 23/10/2009 03:00
> >
> > To
> > Rules Users List <rules-users@lists.jboss.org>,
> > Alan.Gairey@tessella.com
> > cc
> > Rules Users List <rules-users@lists.jboss.org>
> > Subject
> > Re: [rules-users] [droolsflow] Code-based constraints for
> EventWait
> > nodes
> > - is this possible?
> >
> >
> >
> >
> >
> >
> > No, the constraint of an EventWait node (or the State node in
> Drools
> > 5.1) can only be rule-based.  The reason for this is that the rule
> > engine knows when to re-evaluates rules (based on the evailable
> > input).
> >  If you would use a code-based constraint, the engine would have
> no
> > idea
> > when this code constraint might become true (if it was false at
> the
> > start).  Only constant re-evaluation of the code constraint could
> > achieve this (which would be tremendously inefficient).  Could you
> > explain why you would like to have this behaviour?  Maybe there is
> > an
> > alternative way to model this.
> >
> > To change the value of a variable from inside the process (using
> an
> > action), simply use kcontext.setVariable(name, value).  We do not
> > recommend manually changing the value of a process variable from
> > outside
> > the engine.  Again, could you explain why you would like to have
> > this
> > functionality?
> >
> > Kris
> >
> > Quoting Alan.Gairey@tessella.com:
> >
> > > Can the constraint for an EventWait node in a flow be code-based
> > > (rather
> > > than rule-based)? The Eclipse plug-in (v 5.0.1) doesn't allow
> this
> > to
> > > be
> > > specified, unlike say for a Split node, although the relevant
> XML
> > can
> > > of
> > > course be edited.
> > > Trying to load such a process flow results in a
> > NullPointerException,
> > >
> > > because the constraint is always interpreted as a rule.
> > >
> > > Ideally what I'd like to do is have an EventWait node where the
> > > constraint
> > > tests the value of a process variable. This then leads me to
> > another
> > >
> > > question; is there a way of setting the value of a process
> > variable
> > > via
> > > the Drools Flow API?
> > >
> > > Thanks in advance for any help,
> > >
> > > Alan
> > > Tessella plc
> > > 26 The Quadrant, Abingdon Science Park, Abingdon, Oxfordshire,
> > OX14
> > > 3YS
> > > E: Alan.Gairey@tessella.com, T: +44 (0)1235 555511, F: +44
> (0)1235
> > > 553301
> > > www.tessella.com    Registered in England No. 1466429
> > >
> > > This message is commercial in confidence and may be privileged.
> It
> > is
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