You're doing nothing wrong. At least, as long as you want it to print twice. :) Two activations are put on the agenda because both patterns (X+Y and X+Z) are in working memory.

Probably your best bet is to split it into two rules in an activation-group.

rule "Cannot select X if both Y and Z are not selected"
activation-group foo
when
      Item(code == "X")
      not Item(code == "Y")
then
    System.out.println("Error: You cannot select X unless both Y and Z are selected");
end

rule "Cannot select X if both Y and Z are not selected"
activation-group foo
when
      Item(code == "X")
      not Item(code == "Z")
then
    System.out.println("Error: You cannot select X unless both Y and Z are selected");
end

Activation of one rule will prevent activation of the other one, resulting in only one error message.

--- On Mon, 12/1/08, Vithal Kuchibhotla <vithalklrk@rediffmail.com> wrote:

From: Vithal Kuchibhotla <vithalklrk@rediffmail.com>
Subject: [rules-users] Action firing twice
To: rules-users@lists.jboss.org
Date: Monday, December 1, 2008, 11:20 PM

Hello All,

I have a list of Items that I am inserting into working memory. Here is the rule that is failing:

rule "Cannot select X if both Y and Z are not selected"
when
    Item(code == "X")
    (or (not Item(code == "Y"))
        (not Item(code == "Z")))
then
    System.out.println("Error: You cannot select X unless both Y and Z are selected");
end

This rule works correctly when X and Y are there, and when X and Z are there. However, when both Y and Z are missing, the error prints twice. Can anyone tell me what I am doing wrong.

Thanks a lot
Vithal
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