[rules-users] Filtering inside the LHS

[Wolfgang Laun]

Using queries doesn't solve the Hezi's problem which is the selection
of an operator based on some property value.

Relying on Java and evel, you can always write an expression such as

eval( $ctxt.state == SContextState.ONE ?
         $ds.sentence.equals( $someSentence ) :
         $ds.sentence.memberOf( $sentenceSet ) )

(Sorry, I did not try to stick to your complex class structures.)

-W


On 23/02/2012, Mark Proctor <mproctor at codehaus.org> wrote:
> On 23/02/2012 03:38, Hezi Stern wrote:
>>
>> Hi All,
>>
>> I am seeking some kind of filtering (if statement) inside the LHS.
>>
>> I have the following example rule (note: $attributeFilteredSentences
>> and $cmdescriptor are defined in the extends rule which is not presented):
>>
>> *rule*" choose message sentence example"extends "
>> attributeFilteredSentences  collection"
>>
>> *when*
>>
>>                               SContextState(state == SContextState.ONE)
>>
>>             $sentences:       ArrayList()
>>
>> *from**collect*(Sentences.Sentence(
>>
>>
>>    descriptor.meanings.meaning == $cmdescriptor.meanings.meaning
>>
>>                                                                      )
>> *from*  $attributeFilteredSentences)
>>
>> *then*
>>
>>             logger.info("RULE: entered rule:
>> "+drools.getRule().getName());
>>
>> //some logic...
>>
>> *end*
>>
>> **
>>
>> as can be seen I am filtering sentences based on the meanings, and the
>> meaning collection must be identical as in $cmdescriptor (this is the
>> case when SContextState.ONE)
>>
>> Now to my question: I have cases ((this is the case when
>> SContextState.TWO) where I do not need exact validation but rather
>> superset of (for this I have a supersetOf operator implemented)
>>
>> I would like to avoid duplicating  this rule (as I have similar
>> condition in many other rules) and being able to filter once with "=="
>> and once with "supersetOf" depending on the SContextState.
>>
> I have found that query's can be used to provide re-usable rule
> fragments. In the example below I could have inlined the intentory LHS
> in the updateInventory rule, but instead I separated it out into a query
> so that multiple rules can re-use it. There is a small performance
> overhead from using queries, compared to normal patterns, but in most
> cases this is compensated by more maintainable and readable code.
>
> query inventory(Character $char, List $inventory)
>      $char := Character()
>      $inventory := List() from accumulate( Holding( $char, $thing; ),
>                                            collectList( $thing ) )
> end
>
> rule updateInventory salience 5 when
>      SessionCharacter( $char : character, $us : session )
>      inventory( $char, $things; )
> then
>      $us.channels["inventory"].send( $things );
> end
>
>
> Mark
>>
>> Any ideas how to do this?
>>
>> Thanks,
>>
>> Hezi
>>
>>
>>
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>
>