[rules-users] Calling EntityManager from DRL--DRL Parser attemptsto parse sql query instead of passing as string tocreateNativeQuery method

[Anstis, Michael (M.)]

Keyword "From" allows for the retrieval of facts from outside the rule
engine, whereas "memberOf" works upon fact attributes.
 
So these would (should!) be other alternatives:-
 
when
    $p : Property() from (em.createNativeQuery("select PROP from
SAMPLEOBJECT").getResultList()))
    SampleObject(properties contains $p )
then
    ...
end
 
when
    $p : Property() from (em.createNativeQuery("select PROP from
SAMPLEOBJECT").getResultList()))
    SampleObject($p memberOf properties )
then
    ...
end

With kind regards,
 
Mike

________________________________

	From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of David Siefert
	Sent: 07 July 2008 16:21
	To: Rules Users List
	Subject: Re: [rules-users] Calling EntityManager from DRL--DRL
Parser attemptsto parse sql query instead of passing as string
tocreateNativeQuery method
	
	
	Thanks Wilson for the fast reply.
	 
	I did this and almost got it working (mostly due to my newb
knowledge of writing rules).  However, I tinkered with the rule a bit
further, and it turns out i got my original rule post working by simply
using memberOf instead of from!  Not sure why that is....
	 
	-David
	
	
	On Mon, Jul 7, 2008 at 10:45 AM, Wilson O Ojwang
<wojwang at alcatel-lucent.com> wrote:
	

		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
			
________________________________


			_______________________________________________
			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
		
		


-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.jboss.org/pipermail/rules-users/attachments/20080707/d61833fd/attachment.html