Drools: Prioritize fact matching based on a field's value

Question

Consider the following scenario in Drools: We have a rule, matching objects of type A and B against each other.

rule 1
    when
        $a : A()
        $b : B($a.matches($b), flagged == false)
    then
        mofidy($b) { flag($a) }
end

However, A objects have a field called priority, and when a B arrives in the working memory, a matching A with the highest priority should flag it, above all other matching As. How is this possible in Drools? How does it affect performance?

Answer 1

Assuming that B.flag() is setting its flagged attribute to true, you can try something like this:

rule 1
when
    $a : A()
    not A(this != $a, priority > $a.priority)
    $b : B($a.matches($b), flagged == false)
then
    mofidy($b) { flag($a) }
end

One thing to notice in this example is that if an A object with a high priority is inserted, any B that was already flagged with a lower A will not be reflagged.

If you need to reflag yours Bs, then you can try something like this:

rule 1
when
    $a : A()
    not A(this != $a, priority > $a.priority)
    $b : B($a.matches($b), flag != $a)
then
    mofidy($b) { flag($a) }
end

Hope it helps,