How to create the "last" rule in Drools retracting the event if no other rules fire? - drools

Question

I have two rules: one generates the alert message and appending it to the list of strings attribute of event (there will be multiple such rules in future), and the other one retracts event if no alerts was generated.
I use salience for setting the rules priority (the "last" rule should fire literally last). But the rules order is wrong for some reasons so the alerts list is still empty and all the events are retracted. Please look at my samples below.
MainHello.scala
import org.json4s._
import org.json4s.jackson.Serialization.write
import org.kie.api.KieServices
import org.kie.api.builder.Message
import org.kie.internal.io.ResourceFactory
object MainHello {
implicit val formats = DefaultFormats
val events = List(
new Event(123L, null, null),
new Event(456L, null, null),
new Event(789L, null, null),
new Event(688723L, null, null),
new Event(12L, null, null),
new Event(13L, null, null))
def main(args: Array[String]): Unit = {
val kieService = KieServices.get()
val repository = kieService.getRepository
val kfs = kieService.newKieFileSystem
kfs.write(ResourceFactory.newClassPathResource("hello.drl", this.getClass))
val kb = kieService.newKieBuilder(kfs)
kb.buildAll
if (kb.getResults.hasMessages(Message.Level.ERROR)) {
throw new RuntimeException("Build Errors:\n" + kb.getResults.toString)
}
val kContainer = kieService.newKieContainer(repository.getDefaultReleaseId)
val session = kContainer.newKieSession()
events.foreach { item =>
println("INPUT OBJECT: " + write(item))
val facthandle = session.insert(item)
session.fireAllRules()
println("result object: " + write(session.getObject(facthandle)))
}
}
}
Event.java
import java.util.ArrayList;
import java.util.List;
public class Event implements java.io.Serializable {
static final long serialVersionUID = 1L;
private java.lang.Long event_id;
private java.lang.String alert;
private java.util.List<java.lang.String> alerts;
public Event() {
}
public java.lang.Long getEvent_id() {
return this.event_id;
}
public void setEvent_id(java.lang.Long event_id) {
this.event_id = event_id;
}
public java.lang.String getAlert() {
return this.alert;
}
public void setAlert(java.lang.String alert) {
if (alerts == null) {
alerts = new java.util.ArrayList<java.lang.String>();
}
alerts.add(alert);
this.alert = alert;
}
public java.util.List<java.lang.String> getAlerts() {
return this.alerts;
}
public void setAlerts(java.util.List<java.lang.String> alerts) {
this.alerts = alerts;
}
public Event(java.lang.Long event_id, java.lang.String alert,
java.util.List<java.lang.String> alerts) {
this.event_id = event_id;
this.alert = alert;
this.alerts = alerts;
}
}
Hello.drl
rule "alert"
when
e: ru.test.Event(event_id == 123)
then
modify(e) {
setAlert("alert")
}
end
rule "Retract" salience -1
when
e: ru.test.Event (alerts == null || alerts.empty == true)
then
retract(e);
end
console output
INPUT OBJECT: {"event_id":12,"alert":null,"alerts":null}
result object: null
INPUT OBJECT: {"event_id":13,"alert":null,"alerts":null}
result object: null
INPUT OBJECT: {"event_id":123,"alert":null,"alerts":null} // This object should not be retracted because "123" event_id generates alert
result object: null
As you can see, all the events become null.
Drools version is 7.8.0.Final.
What am I doing wrong? Thanks!