[drools-user] Binding a variable to the outcome of an exists()

[Geoffrey De Smet]

I have a rule like this:

rule teacherCanOnlyTeachOneGroupAtATime
  when
    $lesson : Lesson($id : id, $teacher : teacher, $timeslot : timeslot);
    exists Lesson(id > $id, teacher == $teacher, timeslot == $timeslot);
  then
    assertLogical(new HardConstraint(new Object[]{$lesson}, 1));
    // new HardConstraint(causesToUseInEqualsMethod, weight)
end

This leads to a false HardConstraint (after a while of using the same 
workingMemory).
I suspect this is because the HardConstraint's equals() method only 
verifies versus the $lesson, while it should also verify versus the list 
of existing lessons?
But it can't do "$lessonList : exists Lesson(...)".

--
With kind regards,
Geoffrey De Smet


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