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Drools JBoss Rules 5.X Developer's Guide by Michal Bali

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Writing transformation rules

Now that all objects are in the knowledge session, we can start writing some transformation rules. Let's imagine that in the legacy system there are many duplicate addresses. We can write a rule that removes such duplication:

rule twoEqualAddressesDifferentInstance
  when
    $addressMap1 : Map( this["_type_"] == "Address" )
    $addressMap2 : Map( this["_type_"] == "Address", 
      eval( $addressMap1 != $addressMap2 ), 
      this == $addressMap1 )
  then
    retract( $addressMap2 );
    validationReport.addMessage(
      reportFactory.createMessage(Message.Type.WARNING, 
      kcontext.getRule().getName(), $addressMap2));
end

Code listing 4: Rule that loads all Addresses for a Customer into the rule session (file dataTransformation.drl)

The rule matches two addresses. ...

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