Drools rule fire only for inserted event

问题

I have a multiple uses with each a sensor that sends pedometer data. I have a rule file that based on the macAddress, fires the rule:

declare Steps
    @role(event)
end

declare User
    @role(fact)
end

rule "MAC"
when
  User( $mac: macAddress ) from entry-point "entrySteps"
then end

rule "ACC STEPS RULE" extends "MAC"
when
    accumulate( Steps( $s : steps , macAddress == $mac )
            over window:time( 1h ) from entry-point "entrySteps"; 
        $fst: min( $s ), $lst: max( $s );
        $lst - $fst < 50 )
then
    System.out.println($lst + "   " + $fst);
    Action.handleAction($mac,"STEPS RULE: get moving!");
end

My User has just a field macAddress and Steps events have the following fields:

double steps;
Date timeStamp;
String macAddress;

Now when I insert an event then for each macAddress, the rule will fire if the number of steps of a user with that macAddress in the last hour is less then 50. So the rule will fire for every macAddress if this condition is fulfilled. But I want that the rule can only fire for the macAddress of the inserted Step event. How can I adjust my rule?

回答1:

Strangely enough, there's also a firing when there is just a User and no Steps for that User, i.e., the window is empty. The output contains minimum and maximum double values - not sure whether this is a bug in Drools.

As a workaround, add a test of the accumulated count, perhaps greater 0 or greater 1.

accumulate( Steps( $s : steps , macAddress == $mac )
        over window:time( 1h ) from entry-point "entrySteps";
    $fst: min( $s ), $lst: max( $s ), $cnt: count( $s );
    $cnt > 0, $lst - $fst < 50 )

来源：https://stackoverflow.com/questions/36008719/drools-rule-fire-only-for-inserted-event