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
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