Hi Senlin,

It will be easy to use JPA. Here is an example.
===============
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

Senlin Liang wrote:

So, to use a hibernate session, we are storing data in disk in some
"internal format" used by Drools, and we are not actually
communicating with some relational database systems. Is this correct?

Thanks

On Mon, Jul 7, 2008 at 10:32 PM, Mark Proctor <mproctor@codehaus.org> wrote:

Senlin Liang wrote:

Hi all,

Is there some convinent database interface implemented in Drools
(store and retrieve data from DBMS, such as mysql) ?

I checked the manual, and found no such information. So I am assuming
that I will have to use JDBC. Is it right?

you should use Hibernate to access a database. You can then use then pass
the hibernate session as a global and use the "from" keyword to execute
querries to be filtered through a pattern.

Thanks,
Senlin Liang
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