[rules-users] drools quirks

[Matt Young]

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maybe now would be a good time for some code.  Here is how I am
executing the rules against the object:
        KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();


        KnowledgeBuilder kbuilder =
KnowledgeBuilderFactory.newKnowledgeBuilder();
       
kbuilder.add(ResourceFactory.newByteArrayResource(ruledata),ResourceType.DRL
);
        if ( kbuilder.hasErrors() ) {
            System.err.println( kbuilder.getErrors().toString() );
        }
        kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
        StatelessKnowledgeSession ksession =
kbase.newStatelessKnowledgeSession();
        ksession.execute(document);

Here is the rule:

package sample1

import sample1.bean.EventRulesDocument;
import sample1.bean.Transaction;
import java.util.Date;

rule "Standard processing rule"

    when
          $doc : EventRulesDocument(
            ruleRun == false &&  # <<< Wolfgang
            event != null && event.eventType.eventCode == "testevent" )
    then
   
       Transaction t = new Transaction();
        t.setEvent($doc.getEvent());
        t.setCategory($doc.getEvent().getEventType().getEventCode());
        t.setTransactionAmount($doc.getEvent().getEventAmount());
         t.setCreateTs(new Date());
         t.setUsername($doc.getEvent().getCreateUsername());

        modify( $doc ) {setRuleRun(true)};   # Wolfgang <<<<<<
        modify( $doc ) {addSaveTransaction(t)} ;

       
end

If I take out the 2 lines marked "Wolfgang", the ksession never
returns from the execute() method.

Additionally If any code in the world can be executed in the RHS, then
why shouldn't I just use groovy as my rule language?  At least then, I
can write math like such:
def num1=95;
def num2=90;
def num3=num2/num1;

and all of the math is done with big decimal objects.  IF there is no
restriction on what can be done in the RHS what is the advantage to
using a rules engine over a general purpose scripting language?  The
whole purpose for me choosing drools over Groovy eval() was that I
didn't want to give my users the ability to spawn threads, allocate
massive amounts of memory etc.  

On 09/18/2010 10:59 AM, Wolfgang Laun wrote:
> On 18 September 2010 16:15, Matt Young <solid at youngdev.net
> <mailto:solid at youngdev.net>> wrote:
>
> I just started using drools and this is my first time implementing
> a rules engine.  Everything has been pretty smooth but I have
> some quirks that I am not sure I can live with. 1) for some reason,
> if I execute the Knowlege session against an object, the knowlege
> session never returns.
>
>
>> I don't understand the term "execute...against an object". Do you
>> mean that you have just one fact inserted befor you call
>> fireAllRules()?
>
>> But anyway, this call not returning is almost certainly due to a
>> loop in your rules, or have you made sure that they don't?
>
>
> The only way I can get the ksession to return is to make IF (obj ==
> null) part of the LHS and make modify($input){setObj("complete")}
> part of the RHS This seems like a deficiency since I have users
> writing their own rules, I can see them forgetting this
> requirement.
>
>
>> Writing rules is programming, no holds barred :-)
>
>> Look into Domain Specific Languages (DSL) as a cushion for the
>> unwary.
>
>
>
> IS their a way to get the ksession to firerules only once?  If so
> what does that look like?
>
>
>> kSession.fireUntilHalt( 1 );
>
>
> 2) It seems that any code I want can be executed in the RHS.  I
> could literally execute something like the following in the RHS.
>
> byte[] b= new byte[10000000000000]; // Really big memory waste
>
> I also could just start a bunch of threads.
>
> The point is that I am intending to let the users write their own
> rules but I can't do that if there are no restrictions on how/what
> can be done inside the rules.  Any suggestions?  Are there
> sandboxes or filters I can activate to restrict the RHS?
>
>
>> Again: DSL.
>
>> Also, Rule Templates might be the starting point; it'd depend on
>> what the may be allowed to do.
>
>> And what about good old-fashioned training?!
>
>> -W
>
>

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- -- 
Cheers,
Matt Young
solid at youngdev.net
http://youngdev.net

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