David,

Here is what I did to make this work.

This example assume that you have a Person POJO and you want to query all persons with the age lest than or equal to 20.

public class DroolsTest {

    public static final void main(String[] args) {
        try {

            //load up the rulebase
            RuleBase ruleBase = readRule();
            WorkingMemory workingMemory = ruleBase.newStatefulSession();

         // Start EntityManagerFactory
            EntityManagerFactory emf =
                    Persistence.createEntityManagerFactory("persons");

            // Second unit of work
            EntityManager newEm = emf.createEntityManager();
            EntityTransaction newTx = newEm.getTransaction();
            newTx.begin();

            workingMemory.setGlobal("entity",newEm);
            ArrayList<Person> presult = new ArrayList<Person>();
            workingMemory.setGlobal("presult",presult);
            workingMemory.fireAllRules();

            System.out.println("=============List Results=============");
            for ( Person p : presult ){
                System.out.println("Person: \"" + p.getFirstName() +
                        "\", " + p.getLastName() +
                                     "\", " + p.getAge());
            }
            System.out.println("=============End List Results=====\n\n");
            newTx.commit();
            newEm.close();
         // Shutting down the application
            emf.close();

        } catch (Throwable t) {
            t.printStackTrace();
        }
    }
   /**
     * Please note that this is the "low level" rule assembly API.
     */
    private static RuleBase readRule() throws Exception {
        //read in the source
        Reader source = new InputStreamReader( DroolsTest.class.getResourceAsStream( "/Sample.drl" ) );
        PackageBuilder builder = new PackageBuilder();
        builder.addPackageFromDrl( source );

        //get the compiled package (which is serializable)
        Package pkg = builder.getPackage();

        //add the package to a rulebase (deploy the rule package).
        RuleBase ruleBase = RuleBaseFactory.newRuleBase();
        ruleBase.addPackage( pkg );
        return ruleBase;
    }
}

==============
Here is the rule sample.drl

package com.sample

import com.sample.DroolsTest.Message;
import com.sample.Person;
import javax.persistence.EntityManager;
global javax.persistence.EntityManager entity;
global java.util.ArrayList presult;

rule "age"
    when
        $p: Person() from entity.createQuery("from Person p where p.age <= 20").getResultList();
    then
        presult.add($p);
end

==========

Wilson

David Siefert wrote:

Hello,

I am trying to use the EntityManager within a rule. I pass the EntityManager instance in from my test (currently just a mock of the interface using EasyMock) using setGlobal("em", entitymanager);

so in my drls, I have:

<code>

global javax.persistence.EntityManager em;

</code>

And then I use this in my LHS of the rule with a from:

<code>

rule "query-db"

when

SampleObject(property from (em.createNativeQuery("select PROP from SAMPLEOBJECT").getResultList()))

then

System.out.println("Got an object!");

end

</code>

However, when I run my JUnit test, I get an error saying "unexpected token 'PROP'". So it looks like the Drools parser is trying to interpret what is in my string. Is there a special way to pass a string to the Java operation? Or can I simply not do this? How would I be able to get a result set from the db to use in pattern matching? The rule is dependent upon data from a table to make a decision.

Thanks,

David Siefert
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