Rules language : How to deal with comparing between 2 objects of the same class?

Question

I have a class :

public class FootballPlayer() {

    private int scoredGoals;
    //... some other attributes and some getters and setters
}

I need in my drools file to have a rule to decide who is a better player between 2 comapred players.

The difficulty that I cross is how to compare between the two objects of the same class?

Thank you a lot!

Answer 1

There is no difficulty, only a minor cliff that has to be circumnavigated.

rule "A better scorer"
when
    $f1: FootballPlayer( $score1; scoredGoals )
    $f2: FootballPlayer( $score2; scoredGoals > $score1 )
then
    System.out.println( $f2.getName() + " is better than " + $f1.getName() );
end

Of course, it's possible that two players tie:

rule "Two scorers with equal cpability"
when
    $f1: FootballPlayer( $score1; scoredGoals )
    $f2: FootballPlayer( this != $f1, $score2; scoredGoals == $score1 )
then
    System.out.println( $f2.getName() + " and " + $f1.getName() + " are in the same class" );
end

Note the constraint ensuring that the second one isn't idenfical to the first one! (This is the "cliff".)

You might also be interested in a rule to determine the best:

rule "The best scorer"
when
    $f1: FootballPlayer( $score1; scoredGoals )
    not FootballPlayer( scoredGoals > $score1 )
then
    System.out.println( $$f1.getName() + " is the best" );
end