JBoss Drools: Reasoning on QuickFIX-J data model

I just tried to make a simple JBoss Drools example which could probably handle QuickFIX-J messages. So I created the simplest rule flow, including one RuleSet node, mapped onto a ruleflow-group in a DRL file.


same in textual form:

<?xml version="1.0" encoding="UTF-8"?> 
<process xmlns="http://drools.org/drools-5.0/process"
         xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
         xs:schemaLocation="http://drools.org/drools-5.0/process drools-processes-5.0.xsd"
         type="RuleFlow" name="oms" id="my.oms" package-name="my.oms" >

  <header>
  </header>

  <nodes>
    <start id="1" name="Start" x="16" y="16" width="80" height="40" />
    <actionNode id="2" name="Action" x="128" y="16" width="80" height="40" >
        <action type="expression" dialect="java" >System.out.println("Action Start");</action>
    </actionNode>
    <ruleSet id="3" name="RuleSet" x="240" y="16" width="80" height="40" ruleFlowGroup="my-oms" />
    <actionNode id="4" name="Action" x="352" y="16" width="80" height="40" >
        <action type="expression" dialect="java" >System.out.println("Action End");</action>
    </actionNode>
    <end id="5" name="End" x="464" y="16" width="80" height="40" />
  </nodes>

  <connections>
    <connection from="1" to="2" />
    <connection from="2" to="3" />
    <connection from="3" to="4" />
    <connection from="4" to="5" />
  </connections>

</process>

Next describe to rule in a DRL file:

package my.oms

import quickfix.fix44.NewOrderSingle
import quickfix.field.MinQty

rule "reset minqty"
dialect "mvel" 
ruleflow-group "my-oms"
  when
    $order : NewOrderSingle($qty : minQty)
    MinQty(value == 1.0 || value > 100.0) from $qty
  then
    System.out.println("reset order: " + $order); 
    modify($order){
      $order.set(new MinQty(20));
    }
end

What looks a little strange to me is the when part:

    $order : NewOrderSingle($qty : minQty)
    MinQty(value == 1.0 || value > 100.0) from $qty

I spent just quite a few minutes to figure out why my first version of the rule didn't work as I expected. It seemed to me that it would be more natural to make it just in one line, something like this:

  NewOrderSingle(MinQty(value == 1.0 || value > 100.0))

With a Java code from the Drools examples (which may also are generated when you create a Drools Project with the Drools eclipse plug-in), I run the example and it works fine.

package my.oms;

import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.*;
import org.drools.io.ResourceFactory;
import org.drools.logger.KnowledgeRuntimeLogger;
import org.drools.logger.KnowledgeRuntimeLoggerFactory;
import org.drools.runtime.StatefulKnowledgeSession;

import quickfix.field.MinQty;
import quickfix.fix44.NewOrderSingle;


public class MyOms {

 public static final void main(String[] args) {
  try {
   // load up the knowledge base
   KnowledgeBase kbase = readKnowledgeBase();
   StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
   KnowledgeRuntimeLogger logger = KnowledgeRuntimeLoggerFactory.newFileLogger(ksession, "test");
   // go !
   
   NewOrderSingle order = new NewOrderSingle();
   order.set(new MinQty(1.0));
   
   NewOrderSingle order1 = new NewOrderSingle();
   order1.set(new MinQty(111.0));
   
   NewOrderSingle order2 = new NewOrderSingle();
   order2.set(new MinQty(222.0));
   
   ksession.insert(order);
   ksession.insert(order1);
   ksession.insert(order2);
   ksession.startProcess("my.oms");
   ksession.fireAllRules();
   
   logger.close();
  } catch (Throwable t) {
   t.printStackTrace();
  }
 }

 private static KnowledgeBase readKnowledgeBase() throws Exception {
  KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
  kbuilder.add(ResourceFactory.newClassPathResource("oms.drl"), ResourceType.DRL);
  kbuilder.add(ResourceFactory.newClassPathResource("oms.rf"), ResourceType.DRF);
  KnowledgeBuilderErrors errors = kbuilder.getErrors();
  if (errors.size() > 0) {
   for (KnowledgeBuilderError error: errors) {
    System.err.println(error);
   }
   throw new IllegalArgumentException("Could not parse knowledge.");
  }
  KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
  kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
  return kbase;
 }
 
}

This example just shows that with Drools one may handle even quite complex data model, such as QuickFIX-J's one. Next, it would have real value if I'm able to make do the same via Guvnor.