Question

In my code below, I am using the id property to distinguish between two objects ($stp2 is not $stp1). How can I rather do it at object-level, instead of using some property?

rule "multipleSTPSamePeriod"
    when
        $stp1 : SubjectTeacherPeriod( $id:id, $period:period)
        $stp2 : SubjectTeacherPeriod(id>$id, period==$period)

Answer 1

You can use the “this” special property:

rule "multipleSTPSamePeriod"
    when
        $stp1 : SubjectTeacherPeriod( $period:period )
        $stp2 : SubjectTeacherPeriod( this != $stp1, period==$period)

If you want that behavior on all your rules, though, you can set a knowledge base configuration option and the engine will automatically check that for you without the need to add the constraint to every pattern.

Using a system property or conf file you can set:

drools.removeIdentities = <true|false>

Or using the API:

KnowledgeBaseConfiguration conf = ...
conf.setOption( RemoveIdentitiesOption.YES );