How to obtain the minimum of an updated value in Drools? - drools

Question

I want to use Drools to manage some questions in a form. Depending of the answer of the question, the question score be updated with a value. Then I want to obtain the minimum value of all questions answered in a category.
One example:
Category "Replicant or not?":
You’re in a desert walking along in the sand when all of the sudden you look down, and you see a tortoise, crawling toward you. You reach down, you flip the tortoise over on its back. Why is that?
1. it was an error. (5 points).
2. It is the funniest think to do at a dessert. (3 points).
3. You want to kill the tortoise in the most painful way (1 point).
//More other questions.
At the end of the test, the minimum value for each category will be the used one.
Then I have defined some drools rules to define the score for each one (in a spreadsheet, by I put the rule translations):
rule "Question_1"
when
$qs: Questions(checked == false);
$q: Question(category == 'cat1', question == "q1", answer == "a") from $qs.getQuestions();
then
$q.setValue(5);
$qs.setChecked(true);
update($qs);
end
checked value is used to avoid to reuse the rule when updating. category, question, answer are used for classifying the question.
And then, my rule for calculate the minimum is:
rule "Min value"
when
$qs: Questions(checked == true);
not q:Question($v: value; value < $v) from $qs.getQuestions();
then
$qs.setMinValue($v);
System.out.println("The smallest value is: "+ $v);
end
The error obtained is:
$v cannot be resolved to a variable
Then, the question is: How can I obtain the minimum value of a value setted by a previous rule?

Answer 1

The duplication of "from " can be avoided, using the accumulate CE which is about 25% faster.
rule "getmin"
when
Questions( $qs: questions )
accumulate( Question( $v: value ) from $qs; $min: min( $v ) )
then
System.out.println( "minimum is " + $min );
end

Answer 2

You are trying to get $v from a Fact that doesn't exist: not q:Question($v: value; value < $v) from $qs.getQuestions();
What is the expected value of $v is there is no Question that matches that pattern!?
What the seccond pattern is basically saying is: "there is no Question from Questions.getQuestions() that has a value ($v) and that that value is less than the same value"
What you have to do is to bind $v to the positive pattern. Something like this:
rule "Min value"
when
$qs: Questions(checked == true);
Question($v: value) from $qs.getQuestions()
not Question(value < $v) from $qs.getQuestions();
then
$qs.setMinValue($v);
System.out.println("The smallest value is: "+ $v);
end
Hope it helps,
---EDITED: added missing Question positive pattern