[rules-users] Lists and enums in Drools

[Shannon Lal]

Armaghan,
I am no Drools expert but I ran into something similar to this.  The way I
worked around this was that I used the *eval* expression to perform my
complex comparison.

I am quickly laying out the rule( I am not sure if this is the correct
syntac)

rule "Testing for Alpha"
   salience 100
   when
       $test: AlphaEnumCollectionsWrapperClass(alphaList : alphaList)

>     alpha : AlphaWrapperClass( $type:type, type == Class.ALPHA  )

        *eval(  $test contains &type ) *-- You can add a secondary eval
expression

>
> then
>     System.out.println("Found Loudspeaker Equipment. Who wants to jam that?
> Must resist... Jamming sequence in progress... ");
>     materiel.setJam(true);
> end


I am not sure if this is the correct way of doing this.  If there are some
more experienced Rules guys they may be able to help you with the syntax.

Shannon

2009/5/14 Armaghan Mahmud <mahmud.armaghan at gmail.com>

> Hi,
>
> I need help with constructing rules for my scenario.
>
> I started off by creating enum values in the main java file and comparing
> them with the rules to get different responses for different enum values.
> That was easy.
>
> This time, I'm constructing a list of enum values and passing them into the
> rules engine as well. I would like to configure my rules in such a way that
> when they look for the different enum values, they should also look in the
> list to test if the enum value passed into the rules engine is a member of
> the list or not.  My old rules looked like this:
>
> rule "Testing for Alpha"
> salience 100
> when
>     alpha : AlphaWrapperClass(type == Class.ALPHA)
> then
>     System.out.println("Found Alpha");
>     alpha.isFound(true);
> end
>
> I tweaked the above rule to :
>
> rule "Testing for Alpha"
> salience 100
> when
>     $test: AlphaEnumCollectionsWrapperClass(alphaList : alphaList)
>     alpha : AlphaWrapperClass(type == Class.ALPHA && $test contains type )
> then
>     System.out.println("Found Loudspeaker Equipment. Who wants to jam that?
> Must resist... Jamming sequence in progress... ");
>     materiel.setJam(true);
> end
>
> But I'm seeing the following error:
>
> org.drools.rule.InvalidRulePackage: Unable to create Field Extractor for
> '$test' of '[ClassObjectType classAlphaEnumCollectionsWrapperClass]' in rule
> "Testing for Alpha": [Rule name=Testing for Alpha, agendaGroup=MAIN,
> salience=100, no-loop=false]
>
> I'd greatly appreciate your help.
>
> Thanks,
> Armaghan
>
>
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