Drools Stateful Knowledge Session using persistence

Question

I am creating a Drools stateful session as described in the JBPM persistence documentation: http://docs.jboss.org/jbpm/v5.1/javadocs/org/drools/persistence/jpa/JPAKnowledgeService.html

However, I came across the following exception

javax.persistence.TransactionRequiredException: joinTransaction has been called on a resource-local EntityManager which is unable to register for a JTA transaction.

My code is :

EntityManagerFactory emf = Persistence.createEntityManagerFactory("metadata.model");
Environment env = KnowledgeBaseFactory.newEnvironment();
env.set(EnvironmentName.ENTITY_MANAGER_FACTORY, emf);
env.set(EnvironmentName.TRANSACTION_MANAGER, TransactionManagerServices.getTransactionManager());
env.set(EnvironmentName.TRANSACTION,   TransactionManagerServices.getTransactionManager());
KieServices ks = KieServices.Factory.get();
KieContainer kContainer = ks.getKieClasspathContainer();
KieBase kBase = kContainer.getKieBase();
StatefulKnowledgeSession kSession = JPAKnowledgeService.newStatefulKnowledgeSession(kBase, null, env);

The exception is thrown at the last line. Beforehand, I have bound the JDBC JTA Datasource as described in the aforementioned documentation.

PoolingDataSource ds = new PoolingDataSource();
ds.setUniqueName("jdbc/BitronixJTADataSource");
ds.setClassName("com.mysql.jdbc.jdbc2.optional.MysqlXADataSource");
ds.setMaxPoolSize(3);
ds.setAllowLocalTransactions(true);
ds.getDriverProperties().put("user", "root");
ds.getDriverProperties().put("password", "****");
ds.getDriverProperties().put("URL", "jdbc:mysql://localhost:3306/metadatadb");
ds.init();

I am using the EclipseLink persistence provider alongside the MySQL JDBC driver.

Answer 1

Finally, I have made it work. The most important mistake I was making was that I was trying to use EclipseLink as JPA provider. This approach will not work, since besides the custom persistency classes, Drools uses two other persistency-annotated classes: org.drools.persistence.info.SessionInfo and org.drools.persistence.info.WorkItemInfo. These two contain Date fields which are not annotated with the JPA Temporal annotation. They appear to be tailored specifically for Hibernate.

Another important aspect that came to my attention is the need to add the following line after setting the environment variable:

env.set(EnvironmentName.OBJECT_MARSHALLING_STRATEGIES,
            new ObjectMarshallingStrategy[] {
                    new JPAPlaceholderResolverStrategy(domainEnv),
                    new SerializablePlaceholderResolverStrategy(
                            ClassObjectMarshallingStrategyAcceptor.DEFAULT) });

This is performed in order to announce your intention to persist the current session state using JPA.

The exception I mentioned above was, however, due to the fact that EclipseLink was creating a "ResourceLocal" transaction wrapper even though JTA was explicitly specified in persistence.xml. This is due to the fact that there was no target-server property specified. Consequently, there were no external transaction controllers attached to the database session that was created and the wrapper that was provided simply couldn't support the joinTransaction operation. To work around this issue, add the following line to your persistence.xml file:

<property name="eclipselink.target-server" value="JBoss"/>

and before initializing the datasource, add:

Configuration conf = TransactionManagerServices.getConfiguration();
conf.setJndiUserTransactionName("java:/TransactionManager");

Of course, I am presuming that BTM is being used.