Did you try using:

       AlarmFailureEvent(
           btsNumber == $BTS.number,
           $ID : ID
       )

Note that btsNumber starts with a lowercase letter.

Best,

On Sun, May 30, 2010 at 9:04 PM, Djerir Smail <1983djerir@gmail.com> wrote:
Hello everybody,

*I need help please  **I am new in drools,  to start I am trying to
write some simple examples with drools fusion . I wrote a rule  which
print a message when an alarm is received multiple times during 20
minutes but i get this error
*
    [java] Unable to create Field Extractor for 'BtsNumber' of
'[ClassObjectType event=com.mfe.casestudy.pojo.AlarmFailureEvent]' in
rule 'MaxBtsAlarmrule' : [Rule name='MaxBtsAlarmrule']
    [java] java.lang.IllegalArgumentException: Could not parse knowledge.
    [java]     at
com.mfe.casestudy.test.Tester.prepareKnowledgeBase(Tester.java:73)
    [java]     at com.mfe.casestudy.test.Tester.setUp(Tester.java:43)
    [java]     at com.mfe.casestudy.test.Tester.main(Tester.java:87)
    [java] Exception in thread "main" java.lang.NullPointerException
    [java]     at
com.mfe.casestudy.test.Tester.prepareStatefulKnowledgeSession(Tester.java:58)
    [java]     at com.mfe.casestudy.test.Tester.setUp(Tester.java:44)
    [java]     at com.mfe.casestudy.test.Tester.main(Tester.java:87)
    [java] Java Result: 1
main:


*This is my rule  it calculates  the number of alarms received from one
BTS and if this number  exceeds the threshold it prints a warning message *
rule "MaxBtsAlarmrule"
dialect "mvel"
no-loop true
salience 100
when
   $BTS : BTS()

   # check if the number of alarms of last 20 minutes exceeds
   # the BTS threshold
   $numOfAlarms : Number( intValue > $BTS.threshold )
   from accumulate(
       AlarmFailureEvent(
           BtsNumber == $BTS.number,
           $ID : ID
       )
       over window:time(3) from
       entry-point BTSAlarmStream,
       count($ID)
   )


then
 System.out.println("BTS should  be restarted...");

end

Finally this is the  alarm event class

public class AlarmFailureEvent implements Serializable {

   /**
    *
    */
   private static final long serialVersionUID = 1L;

   public String BtsNumber = "";
   private int code = 0;
   private int ID=0;
   public  AlarmFailureEvent(String BtsNumber, int code ,int ID) {
       this.BtsNumber = BtsNumber;
       this.ID=ID;
       this.code=code;
   }

   public void setID(int iD) {
       this.ID = iD;
   }
   public int getID() {
       return this.ID;
   }
   public void setCode(int code) {
       this.code = code;
   }
   public int getCode() {
       return this.code;
   }

   public void setBtsNumber(String btsNumber) {
       this.BtsNumber = btsNumber;
   }

   public String getBtsNumber() {
       return BtsNumber;
   }

}

*Thank you *
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Esteban Aliverti