[jboss-jira] [JBoss JIRA] (DROOLS-365) Rule attribute for adding inverse of consequence as rule condition

[Davide Sottara (JIRA)]

    [ https://issues.jboss.org/browse/DROOLS-365?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12929098#comment-12929098 ] 

Davide Sottara commented on DROOLS-365:
---------------------------------------

I see what you are trying to do, but I am not sure that such an attribute would be feasible, or even solve your problem. 
What happens if a rule inserts (and modifies, and retracts...) more than one object? And what happens if the same object
is insert by more than one rule?

Have you tried using the EQUALITY assertion behavior and/or the @propertyReactive annotation? The former considers
equivalent (i.e. equals()) object to be the "same" and thus do not activate rules multiple times, regardless of the rule
that generated the objects. The latter allows you to control how rules fire in case of updates.

Best
Davide
                
> Rule attribute for adding inverse of consequence as rule condition
> ------------------------------------------------------------------
>
>                 Key: DROOLS-365
>                 URL: https://issues.jboss.org/browse/DROOLS-365
>             Project: Drools
>          Issue Type: Feature Request
>      Security Level: Public(Everyone can see) 
>    Affects Versions: 5.5.0.Final
>            Reporter: Adar Dembo
>            Assignee: Mark Proctor
>
> I have quite a few rules that look like this:
> {noformat}
> rule "if foo then bar"
>   when
>     Foo($a : a, $b : b)
>     not Bar(a == $a, b == $b)
>   then
>     insert(new Bar($a, $b));
> end
> {noformat}
> This is a fairly common pattern for me: a rule should not activate if the facts generated by its consequence were already asserted. It's a pattern I use extensively to generate linear (i.e. non-repeating) workflows.
> Ideally I'd be able to express it as follows:
> {noformat}
> rule "if foo then bar"
> condition-on-inverse-of-consequence
>   when
>     Foo($a : a, $b : b)
>   then
>     insert(new Bar($a, $b));
> end
> {noformat}
> And {{condition-on-inverse-of-consequence}} would cause Drools to generate the right kind of condition, which would be the inverse of the fact changes made by the consequence.
> I think {{lock-on-active}} is similar but harsher: it prevents the rule from firing a second time altogether, regardless of input. At least, that's based on my reading of the docs. In my example, that would be equivalent to  {{not Bar()}} condition in the rule, which is stricter than {{not Bar(a == $a, b == $b)}}.

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