[rules-users] Calling EntityManager from DRL--DRL Parser attempts to parse sql query instead of passing as string to createNativeQuery method
David Siefert
siefert.david.mailinglist at gmail.com
Mon Jul 7 11:20:39 EDT 2008
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
>
> ------------------------------
>
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