[rules-users] sequencing by business logic/ classcastexception in consequence

[Michael Neale]

In terms of your problem, it seems to be to do with:
PreventieveInsluitingsTitel(previous==secondPosition
the secondPosition is not a compatible class with previous?

I don't have any specific thoughts on computing a sequence in rules,
unfortunately... maybe someone else does ? ;)




On 1/11/07, Joost de Vries <drools at ziener.org> wrote:
>
> Hi,
>
> I'm new to jBoss Rules and I'm hitting a few snags. I appreciate your
> insight.
>
> Among other things I want to use business rules to compute the right
> sequence of actions that conforms to legal business rules.
> The only way I could think of to implement this using rules is to use
> rewriting production rules similar to:
> input: ACCAAAC
> rule:  CA -> AC
>
> My first question is: what other ways are there to compute a sequence that
> conforms to sequencing business rules?
>
> My second question concerns the nullpointerexceptions and
> classcastexceptions I'm encountering in my rules.
> I've got a sequence of C's who are either B's or A's. I.e. C is the common
> superclass. This superclass has the methods:
>
> public C getPrevious();
> public C getNext();
>
> Actually it's in dutch so it's
>
> public class Straf extends InsluitingsTitel {}
> and
> public class PreventieveInsluitingsTitel extends InsluitingsTitel {}
> and
> public abstract class InsluitingsTitel{
> public C getPrevious();
> public C getNext();
> }
>
> The rule is as follows:
>
> rule "WSV 68.1"
>     when
>         // any PreventieveInsluitingsTitel should precede all Straf
>         secondPosition: Straf ( firstPosition: previous )
>         thirdPosition:
> PreventieveInsluitingsTitel(previous==secondPosition, fourthPosition:next)
>     then
>         System.out.println( "switching wsv 68.1 "+secondPosition+"
> "+thirdPosition);
>         thirdPosition.switchWithPrevious();
>         if(firstPosition!=null){
>             modify(firstPosition);
>         }
>         modify( secondPosition);
>         modify( thirdPosition);
>         if(fourthPosition!=null){
>             //in the next statement a classcastexception is thrown
>             modify(fourthPosition);
>         }
> end
>
> results in a classcastexception. The sequence is at that moment { Straf,
> Straf, PreventieveInsluitingsTitel, Straf }  and the middle two items are
> matched by the LHS secondPosition and thirdPosition.
>
> Here's the stacktrace.
>
> java.lang.ClassCastException: org.dji.domein.insgro.Straf
>     at
> org.drools.base.org.dji.domein.insgro.PreventieveInsluitingsTitel$getPrevious.getValue(Unknown
> Source)
>     at org.drools.base.ClassFieldExtractor.getValue (Unknown Source)
>     at org.drools.rule.Declaration.getValue(Unknown Source)
>     at com.sample.Rule_WSV_68_1_0ConsequenceInvoker.evaluate
> (Rule_WSV_68_1_0ConsequenceInvoker.java:22)
>     at org.drools.common.DefaultAgenda.fireActivation (Unknown Source)
>     at org.drools.common.DefaultAgenda.fireNextItem(Unknown Source)
>     at org.drools.common.AbstractWorkingMemory.fireAllRules(Unknown
> Source)
>     at org.drools.common.AbstractWorkingMemory.fireAllRules (Unknown
> Source)
>     at org.dji.domein.insgro.VolgordeTest.main(VolgordeTest.java:32)
> org.drools.spi.ConsequenceException: java.lang.ClassCastException:
> org.dji.domein.insgro.Straf
>     at org.drools.common.DefaultAgenda.fireActivation (Unknown Source)
>     at org.drools.common.DefaultAgenda.fireNextItem(Unknown Source)
>     at org.drools.common.AbstractWorkingMemory.fireAllRules(Unknown
> Source)
>     at org.drools.common.AbstractWorkingMemory.fireAllRules (Unknown
> Source)
>     at org.dji.domein.insgro.VolgordeTest.main(VolgordeTest.java:32)
> Caused by: java.lang.ClassCastException: org.dji.domein.insgro.Straf
>     at
> org.drools.base.org.dji.domein.insgro.PreventieveInsluitingsTitel$getNext.getValue(Unknown Source)
>     at org.drools.base.ClassFieldExtractor.getValue(Unknown Source)
>     at org.drools.rule.Declaration.getValue(Unknown Source)
>     at com.sample.Rule_WSV_68_1_0ConsequenceInvoker.evaluate(Rule_WSV_68_1_0ConsequenceInvoker.java:22)
>
>     ... 5 more
>
> Thanks in advance for your insight.
>
> Regards,
>
> --
> Joost de Vries
>
>
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>
>
>
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