Extends is in there since 5.0.0, and should work in eclipse plugin as well. The integration tests are running fine as well, so there should be no problem.

   What error did you got?

   Edson

2010/3/5 Moe Alkhafaji <moe.alkhafaji@medcpu.com>
Thanks Edson, I will try that. However, I have one follow up question. I tried to use the "extends" command and it did not work (it gave me a syntax error). I am using the latest Drools 5.0 M1. Could it be because the Eclipse Drools plugin does not support this feature yet and if I ignore this error on Eclipse it would still work at runtime?

Thanks!

2010/3/5 Edson Tirelli <ed.tirelli@gmail.com>


      Although I noticed the other day that this is not documented yet, Drools 5.0.x does support rule inheritance. In your case, it would be written as:

rule r1
when
   A()
then
   // do something
end

rule r2 extends r1
when
   B()
then
   // do something else
end

    When using inheritance, the subrule will inherit the whole LHS of the parent rule.

    Integration test here:

http://anonsvn.jboss.org/repos/labs/labs/jbossrules/trunk/drools-compiler/src/test/resources/org/drools/integrationtests/extend_rule_test.drl
http://anonsvn.jboss.org/repos/labs/labs/jbossrules/trunk/drools-compiler/src/test/resources/org/drools/integrationtests/test_RuleExtend.drl

    In your case, you have an extra requirement that if a child rule fires, you don't want the parent rule to fire. My suggestion is either doing this with a logical condition, or adding drools.halt() on the consequence of rules that should stop subsequent firings, or using activation-groups + salience. Example, in the above case, you could have:

rule r1
   activation-group "example rules"
   salience 10
when
   A()
then
   // do something
end

rule r2 extends r1
   activation-group "example rules"
   salience 20
when
   B()
then
   // do something else
end

   Since rule 2 has a higher salience, if it activates it will fire first, and due to the activation-group, it will cancel the activation of r1 preventing it to fire.

   Hope it helps.

   Edson

2010/3/5 malkhafaji <moe.alkhafaji@medcpu.com>


Hello,

I know, from searching this forum and posting before, that the concept of
inheritance does not exist today in Drools. However, I have a need for it.
Here is my specific situation:

I have certain rules that have some generic conditions to be fired:

Rule 1
If A Then X end

Rule 2
If A, B Then Y end

What I would like to do is, if Rule 2 is true, then I don't want Rule 1 to
execute. I have many and many of those rules, so combining all the
conditions in less number of rules violates our design having rules being
mutually exclusive. That is why I wanted to include this behavior as a
natural inheritance behavior rather than forcing the flow with logic inside
the rule itself (you will make rules aware of others this way).

So, since there is not built-in feature that allows you to do that, do
people suggest anything that I can do without having to mix Rule 1 and Rule
2 into one rule with complex conditional statements? Any ideas?

The only thing I can think of is taking this logic processing outside of
drools, which is something that I am not too excited about.

Thanks.

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 JBoss by Red Hat @ www.jboss.com

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Phone: (630) 290-1113
Email: cto@medcpu.com

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