[eclipselink-users] RCP-Eclipselink Classloader Problem

["Markus Franz" <markus.franz@xxxxxxxxxxx>]

Title: RCP-Eclipselink Classloader Problem

Hi all,

first and foremost: i am new to the whole ORM stuff, so please be gentle...

While i already did some serious research into the usage of Eclipselink in RCP Applikations, i found no satisfactory answers as to how i can maintain the most flexibility with resspect to the underlying database as well as the stored entities.

I will give you a quick sketch of what i am trying to accomplish:

I want the something like following plugin structure:

 - my.project.persistence (the Plugin providing the Eclipselink features to whoever needs them, defining Extension Points, e.g. for confoguration of the underlying database)

 - my.project.persistence.derby (one of potentially many swappable plugins, extending the aforementioned Extension Points and delivering the database Drivers, Confogurations, etc.)

 - my.project.model (one of potentially many plugins containing some kind of objects, which should be persisted)

 - my.project.application (doing something with the objects from e.g. my.project.model and sometimes try to persist them using my.project.persistence)


What i already got running is an extensibe mechanism to plug in the my.project.persistence.derby plugin on top of the my.project.persistence plugin. Some test object defined inside of the my.project.persistence plugin was successfully persisted into my derby DB. For convenience, i want something like the following to work:

public static boolean save(Object o){
               
                boolean successfull = false;
               
                EntityManager em = getEntityManagerForObject(o);
                EntityTransaction tx = em.getTransaction();
                try
                {
                    tx.begin();
                    em.persist(o);
                    tx.commit();
                }
                catch (Exception ex){
                        ex.printStackTrace();
                }
                finally
                {
                    if (tx.isActive())
                    {
                        tx.rollback();
                    }
                    else
                        successfull=true;

                    em.close();
                    emf.close();
                }
                return successfull;
        }

with an EntityManager gotten like

private static EntityManager getEntityManagerForObject(Object o) {

                IExtensionRegistry registry = Platform.getExtensionRegistry();
                IExtensionPoint point = registry.getExtensionPoint("my.project", "ORMConfiguration");
                String driver="org.apache.derby.jdbc.EmbeddedDriver";
                String dialect="jdbc:derby";
                for (IExtension extension : point.getExtensions()){
                        for(IConfigurationElement element : extension.getConfigurationElements()){
                                driver = new String(element.getAttribute("JDBCDriverClass"));
                                dialect = new String(element.getAttribute("SQLDialect"));
                        }
                }
               
                Map<String, Object> properties = new HashMap<String, Object>();
               
                properties.put("eclipselink.ddl-generation", "create-tables");
                properties.put("eclipselink.ddl-generation.output-mode", "both");
               
                properties.put("eclipselink.jdbc.url", dialect+":MYDBPATH;create=true");
                properties.put("eclipselink.jdbc.user", "user");
                properties.put("eclipselink.jdbc.password", "password");
                properties.put("eclipselink.jdbc.driver", driver);
               
                properties.put("eclipselink.jdbc.read-connections.min", "1");
                properties.put("eclipselink.jdbc.write-connections.min", "1");
               
                properties.put("eclipselink.logging.level" , "FINE");
                properties.put("eclipselink.logging.timestamp", "false");
                properties.put("eclipselink.logging.session", "false");
                properties.put("eclipselink.logging.thread", "false");
       
               
////////////           THIS IS THE POINT OF INTEREST:           ///////////////////


                properties.put(PersistenceUnitProperties.CLASSLOADER, o.getClass().getClassLoader());
               
               
////////////////////////////////////////////////////////////////////////////////////           
               

                try {
                        emf = new PersistenceProvider().createEntityManagerFactory("my.project", properties);
                } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                }
               
                EntityManager em = emf.createEntityManager();
               
                return em;
        }


A Simple Application (in my.project.application) might now take some Object, let's call it CrashTestDummy ctd1 from my.project.model (where its mapping information is also stored, let's say in a regular orm.xml file) and just call my.project.persistence.Utility.save(ctd1) and eclipselink would do it's magic. I do not know, if this is bad practice, but it seemed to me to be a reasonable approach, if i do not want to touch the my.project.persistence plugin ever again, when i am developing some my.project.model.newstuff style plugins.
The trouble is that without referencing the classloader of the persisted object (i.e. commenting out the indicated line above), there is no trouble loading the database driver and all, but no mapping for the object is found. If i try to run it with the objects Classloader, the output indicates that the mapping is indeed found, but alas not the derby driver!

I assume, this is somehow related to some of the old questions on this mailing list concerning OSGI but i am also not exactly an OSGI crack and therefore could not entirely understand all comments.

Regards

Markus