Re: [rules-users] Stateful session and non-existence of Facts

2009/11/26 Leonardo Gomes <leonardo.f.gomes(a)gmail.com&gt; > > > On Tue, Nov 24, 2009 at 10:42 PM, Leonardo Gomes < > leonardo.f.gomes(a)gmail.com&gt; wrote: > >> H >> >> Now, let's say FactA(1) indicates a fact of type FactA and id = 1. >> >> - Then, in the beginning, I insert FactA(1) and FactA(2) in my working >> memory and fire the rules. >> >> rule "test non existence" >> when >> not FactA( id == 4 ) >> then >> output.add("there's no FactA id 4"); >> >> - This rule is fired and the message is added to my output object. >> >> Later on, I have a notification that a FactA has changed, then I: >> - retract all FactAs from my working memory >> - clear all FactA-related messages from my output object >> - reload FactAs (let's say now I have FactA(1), FactA(3), but NOT >> FactA(4)) >> - reinsert them in the WM >> - fire the rules >> >> The rule that checks that there's no FactA(4) doesn't refire. >> > Why should it? The truth of the non-existance of FactA(4) has been established, and this truth never changed, certainly not by removing any FactA(n) and also not by inserting any FactA(x) with x!= 4. As a solution, you could - establish an explicit fact, asserted in rule "test non existence" and retracted by a rule checking the negated condition; - add a Trigger fact to rule "test non existence" which you modify after each reload of the FactA set - do something else which I'm not clever enough to think about at the moment -W