Drools 6 loading and executing rule from String - drools

Question

I am trying to load a rule from a String in Drools 6 like this:
// the rule
def drl = '''
dialect "mvel"
rule "Person is over 18"
when
$person : Person(age > 18)
then
System.out.println("Person is "+$person.name);
end
'''
// setup for rule
KieServices kieServices = KieServices.Factory.get()
KieFileSystem kfs = kieServices.newKieFileSystem()
kfs.write( "src/main/resources/simple.drl",
kieServices.getResources().newReaderResource( new StringReader(drl) ) )
KieBuilder kieBuilder = kieServices.newKieBuilder( kfs ).buildAll()
// check there have been no errors for rule setup
Results results = kieBuilder.getResults();
if( results.hasMessages( Message.Level.ERROR ) ){
println( results.getMessages() )
throw new IllegalStateException( "### errors ###" )
}
KieContainer kieContainer =
kieServices.newKieContainer( kieBuilder.getKieModule().getReleaseId() )
KieSession kieSession = kieContainer.newKieSession()
// insert facts and fire rules
kieSession.insert(new Person("Jon Doe", 21))
kieSession.insert(new Person("Jon Darcy", 1))
kieSession.fireAllRules()
kieSession.dispose()
#Immutable
class Person {
String name
int age
}
What I wanted to happen is getting the person name printed out. By attaching eventlistener and logger I can see that the facts are added and asserted. By having an error in the drl I can be sure the rule is seen and compiled. But the rule never fires.
I am pretty sure there is jsut a stupid little mistake somewhere in the code. Can somebody help me?

Answer 1

Getting a KieBase from the KieContainer and creating the KieSession from that is what works for me:
KieContainer kieContainer =
kieServices.newKieContainer(kieServices.getRepository().getDefaultReleaseId() );
KieBase kieBase = kieContainer.getKieBase();
KieSession kieSession = kieBase.newKieSession();
But your code is working, too - at least after doing it all in Java, and making sure that Person and the DRL file are in the same package.
String drl = "package drlstring;\n" +
"dialect 'mvel'\n" +
"rule Person_is_over_18\n" +
"when\n" +
"$person : Person(age > 18)\n" +
"then\n" +
"System.out.println(\"Person is \"+$person.getName());\n" +
"end";
// setup for rule
KieServices kieServices = KieServices.Factory.get();
KieFileSystem kfs = kieServices.newKieFileSystem();
kfs.write( "src/main/resources/simple.drl",
kieServices.getResources().newReaderResource( new StringReader(drl) ) );
KieBuilder kieBuilder = kieServices.newKieBuilder( kfs ).buildAll();
// check there have been no errors for rule setup
Results results = kieBuilder.getResults();
if( results.hasMessages( Message.Level.ERROR ) ){
System.out.println( results.getMessages() );
throw new IllegalStateException( "### errors ###" );
}
KieContainer kieContainer =
kieServices.newKieContainer( kieBuilder.getKieModule().getReleaseId() );
KieSession kieSession = kieContainer.newKieSession();
// insert facts and fire rules
kieSession.insert(new Person("Jon Doe", 21));
kieSession.insert(new Person("Jon Darcy", 1));
kieSession.fireAllRules();
kieSession.dispose();
If you want to continue with your Scala setup, narrow the possible causes for the failure to fire down by adding a rule with an empty condition:
rule hello
when then
System.out.println( "Hello!" );
end
I think it is the Scala definition of class Person that isn't recognized by the Drools engine.