[rules-users] One question about Database interface

[Ojwang Wilson O]

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 at 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
>>> _______________________________________________
>>> rules-users mailing list
>>> rules-users at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>
>>>
>>>       
>> _______________________________________________
>> rules-users mailing list
>> rules-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>>
>>     
>
>
>
>   
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