24.8. Pet Store Example: Evaluate Agenda Group from PetStore.drl

// Free Fish Food sample when we buy a Gold Fish if we haven't already bought 
// Fish Food and don't already have a Fish Food Sample
rule "Free Fish Food Sample"
    agenda-group "evaluate"
    dialect "mvel"
when
    $order : Order()
    not ( $p : Product( name == "Fish Food") && Purchase( product == $p ) )
    not ( $p : Product( name == "Fish Food Sample") && Purchase( product == $p ) )
    exists ( $p : Product( name == "Gold Fish") && Purchase( product == $p ) )
    $fishFoodSample : Product( name == "Fish Food Sample" );
then
    System.out.println( "Adding free Fish Food Sample to cart" );
    purchase = new Purchase($order, $fishFoodSample);
    insert( purchase );
    $order.addItem( purchase ); 
end

// Suggest a tank if we have bought more than 5 gold fish and don't already have one
rule "Suggest Tank"
    agenda-group "evaluate"
    dialect "java"
when
    $order : Order()
    not ( $p : Product( name == "Fish Tank") && Purchase( product == $p ) )
    ArrayList( $total : size > 5 ) from collect( Purchase( product.name == "Gold Fish" ) )
    $fishTank : Product( name == "Fish Tank" )
then
    requireTank(frame, drools.getWorkingMemory(), $order, $fishTank, $total); 
end
The rule "Free Fish Food Sample" will only fire if:
  • The store does not already have any fish food, and
  • The store does not already have a free fish food sample, and
  • The store does have a Gold Fish in its order.
The rule "Suggest Tank" will only fire if
  • The store does notalready have a Fish Tank in its order, and
  • The store does have more than five Gold Fish Products in its order.
  • If the rule does fire, it calls the requireTank() function . This shows a Dialog to the user, and adding a Tank to the order and Working Memory if confirmed.
  • When calling the requireTank() function the rule passes the global frame variable so that the function has a handle to the Swing GUI.
  • If the rule does fire, it creates a new product (Fish Food Sample), and adds it to the order in Working Memory.
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