[rules-users] [droolsflow] Code-based constraints for EventWait nodes - is this possible?

Wed Oct 28 08:54:43 EDT 2009

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 at cs.kuleuven.be> 
28/10/2009 10:40

To
Alan.Gairey at tessella.com
cc
Rules Users List <rules-users at 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 at 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 at cs.kuleuven.be> 
> 23/10/2009 03:00
> 
> To
> Rules Users List <rules-users at lists.jboss.org>,
> Alan.Gairey at tessella.com
> cc
> Rules Users List <rules-users at 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 at 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 at tessella.com, T: +44 (0)1235 555511, F: +44 (0)1235
> > 553301
> > www.tessella.com    Registered in England No. 1466429
> > 
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