The work item in the attached test case, the first time it executes sets a property on a fact in memory that causes a subsequent Split node to send the flow to an Event Wait. The code in the overall main() method (in PersistenceTest.java) then updates the fact in memory so that the Event Wait's constraint is satisfied, and the work item node is executed again. The second time around, it sets the property on the fact in memory so that the subsequent Split node sends the flow to its end. (I hope this makes sense; looking at the rule flow in the test case should show you what I'm trying to do.)

If I execute the test case with my session created using the code:

  StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();

everything works as I would expect, and the output from the System.out.println() statement in my getCurrentNodeId() method above is:

  Node instance: org.drools.workflow.instance.node.WorkItemNodeInstance@125d568
  Node instance: org.drools.workflow.instance.node.WorkItemNodeInstance@37a04c

However, if I use JPA persistence:

  StatefulKnowledgeSession ksession = JPAKnowledgeService.newStatefulKnowledgeSession(kbase, null, env);

then the RuntimeException in getCurrentNodeId() is thrown, and the output is:

  Node instance: org.drools.workflow.instance.node.WorkItemNodeInstance@2209db
  Node instance: org.drools.workflow.instance.node.MilestoneNodeInstance@d8fd1a

Somehow it seems as though the node instance isn't quite synchronised with the overall state when using JPA persistence.

Any help you could give me here would be very much appreciated.

Regards,

Alan

Kris Verlaenen <kris.verlaenen@cs.kuleuven.be> 30/10/2009 20:10

To Alan.Gairey@tessella.com cc Subject Re: [rules-users] [droolsflow] Code-based constraints for EventWait nodes - is this possible?

Alan,

Thanks, this indeed seems to be the issue.  I have changed this on
trunk.  Does adding this null check solve your issue?

Thx,
Kris

Quoting Alan.Gairey@tessella.com:

> 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
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