Using QueryResults does not return anything - drools

Question

I am trying to count the number of objects by using QueryResults. My rule is:
query "Test"
m : Message()
end
function int countFacts(String queryString) {
QueryResults queryResults = DroolsTest.getQueryResults(queryString);
if (queryResults != null) {
System.out.println("Total FACTS found: " + queryResults.size());
return queryResults.size();
}
return 0;
}
rule "Hello World"
when
m : Message( status == Message.HELLO, myMessage : message )
eval(countFacts("Test")>0 )
then
System.out.println( myMessage );
end
And in the java side
public static QueryResults getQueryResults(String queryName) {
System.out.println("inside queryResults for queryName " +queryName );
QueryResults queryResults = kSession.getQueryResults(queryName);
return queryResults;
}
When I am trying to run the rule, execution stops and nothing happens.
The kSession.getQueryResults(queryName) returns nothing and after some time I have to manually terminate the execution.
what is wrong here?

Answer 1

I think the issue here is your thread being blocked. If your requirement is to count the number of facts in your session as part of a rule, then you can do it in a much more "Drools-friendly" way using an accumulate:
rule "More than 2 HELLO messages"
when
Number(longValue > 2) from accumulate (
Message( status == Message.HELLO),
count(1)
)
then
System.out.println( myMessage );
end
If you really want to call a query from the when part of a rule, you will need to pass an unbound variable to the query in order to get the result back in your rule:
query countMessages(long $n)
Number($n:= longValue) from accumulate (
Message(),
count(1)
)
end
rule "Hello World"
when
m : Message( status == Message.HELLO, myMessage : message )
countMessages($n;)
eval($n > 0)
then
System.out.println( m );
end
Hope it helps,