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

[Kris Verlaenen]

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 at 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 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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