[rules-users] Calling EntityManager from DRL--DRL Parser attempts to parse sql query instead of passing as string to createNativeQuery method

[David Siefert]

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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