10:30 a.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(a)lists.jboss.org
[mailto:rules-users-bounces@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(a)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
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