[rules-users] How can I use retract in action or exception handler?

[Swindells, Thomas]

> Thanks, it helps.
> But there are some more questions.
> 1. What is an official name of rule language, if it is not MVEL? Why "MVEL
> dialect" in split constraints allow using code like:
>         $p: Person ( age > 21 )
DRL - presumably standing for Drools Rule Language
> 2. Why it is not possible to use rules in actions in MVEL mode? I suppose it
> would be useful.
What do you actually mean by using a rule in an action..
The answer is likely to be it is due to the way that rules are declarative and not procedural and how the Rete algorithm works.
> 3. How can I create new object in the constraint? For example, I have a
> constraint:
>
> $p : Person( age < 21 )
>
> - in this branch I need to create the new object "PersonFault" and insert it
> to the working memory, but the code :
>
> $p : Person( age < 21 )
> $fault = new PersonFault($p, "WRONG AGE");
> kcontext.getKnowledgeRuntime().insert($fault);
>
> - is not working. Nor in the constraint, nor in the action...

It won't work in the constraint as it doesn't make sense to create objects in the constraint.
The standard way to do it is as follows - also note the knowledge runtime methods are exposed directly (see http://downloads.jboss.com/drools/docs/5.0.1.26597.FINAL/drools-expert/html_single/index.html#d0e5216)

Rule "foo"
when
$p : Person(age < 21)
then
 insert(new PersonFault($p, "WRONG AGE"));
end

Thomas


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