[rules-dev] IRC: interesting topic: use of lists using "from" in LHS and iterated over in RHS

[Mauricio Salatino]

One rules is fired per cycle, so it depends the rules that it's fired first.
You are right it's totally up to the conflict resolution strategy.


On Fri, Aug 6, 2010 at 12:04 PM, Anstis, Michael (M.) <manstis1 at ford.com>wrote:

>  HI,
>
> There was an interesting discussion today on IRC; a user "jochen" reported
> NPEs when trying to iterate lists in the RHS constructed in the LHS using
> "from collect".
>
> I was wondering how Drools handles lists constructed in the LHS; if the
> list contained 5 elements but another rule retracted one of those elements
> would the list available in the RHS contain 4 or 5 elements?
>
> Here's a simplification of what was posted at *
> http://pastebin.com/yKGSxFkA* <http://pastebin.com/yKGSxFkA>
>
> Rule 1
> when
>         $cheese : ArrayList() from collect(CheeseFact());
> then
>         for(int i=0; i<$cheese.size(); i++) {
>                 //Something useful…
>         }
> end
>
> What if there was another rule that did something like this:-
>
> Rule 2
> When
>         $cf : CheeseFact(type == "chedder")
> Then
>         retract($cf);
> end
>
> What would be the list Rule 1 iterates?
>
> I'd assume since I believe activation execution to be serial it would
> depend on the agenda's conflict resolution strategy or rule salience?
>
> What would be the learned opinion?
>
> With kind regards,
>
> Mike
>
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>


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