[rules-users] How to limit results from a collect statement

[pentarious]

I know. Actually I didn't put any update or insert statement in the code just
to make it simpler. The actual code looks like:
when
      $itemList : ArrayList() from collect( Item( category == "VIDEO" ) )
then
      ItemDiscount disc = new ItemDiscount(10);
      insert(disc);
      $myFirstItem = (Item)$itemList.get(0);
      $mySecondItem = (Item)$itemList.get(1);
      $myFirstItem.addDiscount(disc);
      $mySecondItem.addDiscount(disc);
      update($myFirstItem);
      update($mySecondItem);
Now, why this doesn't work at all? It does work if I write a rule for each
item using in the when clause $item  : Item from $itemList, but as I said I
need to write a list-oriented rule.

Regards,

CG


Edson Tirelli-3 wrote:
> 
>    If you want the "engine to see" your changes, in a way you affect other
> rules, you must call update( object ) for the object you are changing.
> Otherwise, the change will happen to the original object, but not to the
> shadow proxy that the engine uses to ensure consistency.
> 
>    []s
>    Edson
> 
> 2007/8/22, pentarious <cristiano.giuffrida at gmail.com>:
>>
>>
>> Ok, I'm still working on that, I'll publish my solution asap. In the
>> meantime
>> it turns out our requirements need something more than that. We have an
>> ordered list of beans (items) and we have to be able to modify a specific
>> subset of the list (adding a discount). Now I tried to solve this problem
>> by
>> working directly on the list of items. But I can't understand why this
>> doesn't work:
>> when
>>      $itemList : ArrayList() from collect( Item( category == "VIDEO" ) )
>> then
>>      ItemDiscount disc = new ItemDiscount(10);
>>      $myFirstItem = (Item)$itemList.get(0);
>>      $mySecondItem = (Item)$itemList.get(1);
>>      $myFirstItem.addDiscount(disc);
>>      $mySecondItem.addDiscount(disc);
>>
>> After executing this rule it's like nothing happened! I mean no discount
>> has
>> been added to the two items! The problem seems to be related to
>> extracting
>> items from the list. Apparently, every time we get an item from the list,
>> it
>> looses its link with the original item (I don't know if it's a copy of
>> the
>> original item or whatever), so that every update doesn't affect the
>> original
>> item any more. But of course that's what we're interested in! We want to
>> modify original items in the rule session. Am I missing something? Or Is
>> it
>> a bug?
>>
>> Regards,
>>
>> CG
>>
>>
>>
>> Edson Tirelli-3 wrote:
>> >
>> >     Please, share with us! Send to the list!
>> >
>> >     Edson
>> >
>> > 2007/8/21, pentarious <cristiano.giuffrida at gmail.com>:
>> >>
>> >>
>> >> I found an interesting implementation to do that. If anyone is
>> interested
>> >> I
>> >> could share my solution.
>> >>
>> >> Regards,
>> >>
>> >> CG
>> >>
>> >>
>> >> Mark Proctor wrote:
>> >> >
>> >> > There is no supported way to do this. You could use an inline-eval
>> >> > against a global, but that is very clunkey. However it does seem
>> like
>> a
>> >> > good feature idea for a future release, open a jira and I'll look
>> into
>> >> > getting it included.
>> >> >
>> >> > Mark
>> >> > pentarious wrote:
>> >> >> Does anyone know a method to limit the number of results from a
>> >> collect
>> >> >> statement? I was just wondering how to do something like this:
>> >> >> $myList : List() from collect( MyObject(myField == "something") )
>> >> limit
>> >> 3
>> >> >> //it should put in $myList just the first 3 objects retrieved
>> >> >> I'm quite sure there is nothing in Drools which can natively
>> support
>> >> >> something like that. So, how to do that, if needed? I tried this,
>> but
>> >> it
>> >> >> seems not to be working (I can't understand why, though):
>> >> >> $myList : List() from collect( MyObject(myField == "something") )
>> >> >> $myObject : MyObject() from $myList
>> >> >> eval( $myList.indexOf($myObject) < 3 )
>> >> >> Indeed, it doesn't work because the link beetween $myList and
>> >> $myObject
>> >> >> seems to be released during any execution of the rule (In fact
>> >> >> $myList.contains($myObject) returns false! Again, I can't
>> understand
>> >> >> why...)
>> >> >>
>> >> >> Any advice would be really appreciated!
>> >> >>
>> >> >> Regards,
>> >> >>
>> >> >> CG
>> >> >>
>> >> >
>> >> > _______________________________________________
>> >> > rules-users mailing list
>> >> > rules-users at lists.jboss.org
>> >> > https://lists.jboss.org/mailman/listinfo/rules-users
>> >> >
>> >> >
>> >>
>> >> --
>> >> View this message in context:
>> >>
>> http://www.nabble.com/How-to-limit-results-from-a-collect-statement-tf4235669.html#a12249025
>> >> Sent from the drools - user mailing list archive at Nabble.com.
>> >>
>> >> _______________________________________________
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>> >>
>> >
>> >
>> >
>> > --
>> >   Edson Tirelli
>> >   Software Engineer - JBoss Rules Core Developer
>> >   Office: +55 11 3529-6000
>> >   Mobile: +55 11 9287-5646
>> >   JBoss, a division of Red Hat @ www.jboss.com
>> >
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>> >
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> 
> 
> 
> -- 
>   Edson Tirelli
>   Software Engineer - JBoss Rules Core Developer
>   Office: +55 11 3529-6000
>   Mobile: +55 11 9287-5646
>   JBoss, a division of Red Hat @ www.jboss.com
> 
> _______________________________________________
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