Conceptual meaning of 'not' keyword; evaluating between objects

Question

I am trying to find a BucketTotal object which has the smallest total in a Drools Planner project. I adapted this from example code.

rule "insertMinimumBucketTotal"
when
   $b : BucketTotal($total : total)
   not BucketTotal(total > $total) // CONFUSED HERE
then
   insertLogical(new MinimumBucketTotal($total));
end

As far as my reasoning went, it meant "find BucketTotal object $b, such that there doesnt exist another BucketTotal object whose total is greater than total of $b".

Turns out, it meant the opposite (and I corrected it).

Please explain how Drools reasons that statement to find $b.

score 3 · Accepted Answer · answered Feb 09 '12 at 20:22

Indeed your are confusing things. "not" means "not exists". So if you want to find the minimum total you can do:

rule "minimum"
when
   BucketTotal( $min : total )
   not BucketTotal( total < $min )
then
   // do something with $min
end

The above is usually the more performant way of doing it, but you can also use accumulate if you prefer:

rule "minimum"
when
    accumulate( BucketTotal( $total : total ),
                $min : min( $total ) )
then
    // do something with $min
end

Conceptual meaning of 'not' keyword; evaluating between objects

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