Access to Drools returned fact object in Java Code

Question

I have a drools rule created via the Guvnor console and the rule validates and inserts a fact into the working memory if conditions were met. The rule is:

    1. | rule "EligibilityCheck001" 
    2. |     dialect "mvel" 
    3. |     when 
    4. |         Eligibility( XXX== "XXX" , YYY== "YYY" , ZZZ== "ZZZ" , BBB == "BBB" ) 
    5. |     then 
    6. |         EligibilityInquiry fact0 = new EligibilityInquiry(); 
    7. |         fact0.setServiceName( "ABCD" ); 
    8. |         fact0.setMemberStatus( true ); 
    9. |         insert(fact0 ); 
   10. |         System.out.println( "Hello from Drools"); 
   11. | end

Java code that executes the rule is as follows

RuleAgent ruleAgent = RuleAgent.newRuleAgent("/Guvnor.properties");
RuleBase ruleBase = ruleAgent.getRuleBase();
FactType factType = ruleBase.getFactType("mortgages.Eligibility");

Object obj = factType.newInstance();
factType.set(obj, "XXX", "XXX");
factType.set(obj, "YYY", "YYY");
factType.set(obj, "ZZZ", "XXX");
factType.set(obj, "BBB", "BBB");

WorkingMemory workingMemory = ruleBase.newStatefulSession();
workingMemory.insert(obj);
workingMemory.fireAllRules();
System.out.println("After drools execution");
long count = workingMemory.getFactCount();
System.out.println("count " + count);

Everything looks great with the output as below:

Hello from Drools
After drools execution
count 2

I cannot seem to find a way to get the EligibilityInquiry fact object back in my Java code and get the attributes set in the rule above (serviceName and status). I have used the StatefulSession approach.

The properties file has the link to the snapshot with basic authentication via username and password. There are 2 total facts: EligibilityInquiry and Eligibility.

I am fairly new to drools and any help with the above is appreciated.

laune · Accepted Answer · 2019-08-05T13:56:45.283

(Note: I fixed the order of statement, a typo ("XX") and removed the comments from the output. Less surprise.)

This snippet assumes that EligibilityInquiry is also declared in DRL.

FactType eligInqFactType = ruleBase.getFactType("mortgages", "EligibilityInquiry");
Class<?> eligInqClass = eligInqFactType.getFactClass();
ObjectFilter filter = new FilterByClass( eligInqClass );
Collection<Object> eligInqs = workingMemory.getObjects( filter );

And the filter is

public class FilterByClass implements ObjectFilter {
    private Class<?> theClass;
    public FilterByClass( Class<?> clazz ){
        theClass = clazz;
    }
    public boolean accept(Object object){
        return theClass.isInstance( object );
    } 
}

You might also use a query, which takes about the same amount of code.

// DRL code
query "eligInqs" 
    eligInq : EligibilityInquiry()
end

// after return from fireAllRules
QueryResults results = workingMemory.getQueryResults( "eligInqs" );
for ( QueryResultsRow row : results ) {
    Object eligInqObj = row.get( "eligInq" );
    System.out.println( eligInqClass.cast( eligInqObj ) );
}

Or you can call workingMemory.getObjects() and iterate the collection and check for the class of each object.

for( Object obj: workingMemory.getObjects() ){
    if( obj.isInstance( eligInqClass ) ){
        System.out.println( eligInqClass.cast( eligInqObj ) );
    }
}

Or you can (with or without inserting the created EligibilityInquiry object as a fact) add the fact to a global java.util.List eligInqList and iterate that in your Java code. Note that the API of StatefulKnowledgeSession is required (instead of WorkingMemory).

   // Java - prior to fireAllRules
   StatefulKnowledgeSession kSession() = ruleBase.newStatefulSession();

   List<?> list = new ArrayList();
   kSession.setGlobal( "eligInqList", list );

   // DRL
   global java.util.List eligInqList;

   // in a rule
   then
       EligibilityInquiry fact0 = new EligibilityInquiry(); 
       fact0.setServiceName( "ABCD" ); 
       fact0.setMemberStatus( true ); 
       insert(fact0 );  
       eligInqList.add( fact0 ); 
   end

   // after return from fireAllRules
   for( Object elem: list ){
    System.out.println( eligInqClass.cast( elem ) );
   }

Probably an embarras de richesses.

Thanks for the explanation, but for the same question, if I have to retrieve the fact0 from Drools Rule Execution Server via REST api, how do I do that? — Dminds, May 05 '15 at 09:52
@Dminds did you get the answer for retrieving the fact0 from Drools Rule Execution Server via REST api. — Vaibhav Bhootna, Jul 18 '15 at 20:49
I think in the third example you meant `if( obj.isInstance( eligInqClass ) )` — sgsweb, Jul 03 '19 at 19:50

Access to Drools returned fact object in Java Code

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