Re: [eclipselink-users] Load mapping file at "runtime"

[Christian August Michelsen <chris-m@xxxxxxx>]

Den 05.10.2010 17:35, skrev Tom Ware:
> Hi Christian,
>
> Is it possible to have multiple persitence units that have the same
> entities, but different orm xml files that override the mappings and
> just select the persistence unit that has the override you need.
>
> It is possible to alter the underlying EclipseLink metadata after your
> peristence unit is created, but you need to be careful because there is
> quite alot of code that runs at initialization time to make sure
> everything is consistence. Changing the field a BasicMapping maps to
> should be fairlyl easy, but if you get into changing relationships
> mappings or mappings within InheritanceHierarchies, you will have to be
> quite careful.
>
> org.eclipse.persistence.jpa.JpaHelper has a getServerSession() method
> that can get our underlying session. Session has a project and project
> has a list of mappings that can be acquired by name. Changing the
> mappings is a matter of calling the appropriate methods on the various
> mappings you get back.

I'm having some trouble getting this all to work.
I do like this:

EntityManagerFactory emf = 
Persistence.createEntityManagerFactory("OverridesPU");
EntityManager em = emf.createEntityManager();
Project p = JpaHelper.getServerSession(emf).getActiveSession().getProject();
ClassDescriptor cd = p.getClassDescriptor(ZenOrder.class);

From here I've tried to approaches, one is to create a new mapping via 
DatabaseMapping and the other is to modify an existing mapping.

To modify an existing mapping I tried:
DirectToFieldMapping dm = (DirectToFieldMapping) 
cd.getMappingForAttributeName("paymentOrderId");
dm.setFieldName("dibs_transid"); // the field is not in use on any 
mapping. Just testing and have only mapped a small portion of the table.

Then all I get are null values, if I remove the last line I get one of 
the other columns. And if I add dm.setGetMethodName("...") and the same 
for the setSet-method I get a nullpointerexception.


And if I try to add a DirectToFieldMapping for a @Transient value;
DirectToFieldMapping dm = new DirectToFieldMapping();
dm.setFieldName("zen_orders.dibs_transid");
dm.setAttributeName("paymentOrderId");
cd.addMapping(dm);

I get the following exception:

Exception in thread "main" java.lang.NullPointerException
        at 
org.eclipse.persistence.internal.helper.Helper.isPrimitiveWrapper(Helper.java:1164)
        at 
org.eclipse.persistence.internal.descriptors.InstanceVariableAttributeAccessor.setAttributeValueInObject(InstanceVariableAttributeAccessor.java:198)
        at 
org.eclipse.persistence.mappings.DatabaseMapping.setAttributeValueInObject(DatabaseMapping.java:1368)
        at 
org.eclipse.persistence.mappings.DatabaseMapping.readFromRowIntoObject(DatabaseMapping.java:1259)
        at 
org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildAttributesIntoObject(ObjectBuilder.java:332)
        at 
org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildObject(ObjectBuilder.java:661)
        at 
org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildWorkingCopyCloneNormally(ObjectBuilder.java:583)
        at 
org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildObjectInUnitOfWork(ObjectBuilder.java:552)
        at 
org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildObject(ObjectBuilder.java:492)
        at 
org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildObject(ObjectBuilder.java:444)
        at 
org.eclipse.persistence.queries.ObjectLevelReadQuery.buildObject(ObjectLevelReadQuery.java:635)
        at 
org.eclipse.persistence.queries.ReadAllQuery.registerResultInUnitOfWork(ReadAllQuery.java:838)
        at 
org.eclipse.persistence.queries.ReadAllQuery.executeObjectLevelReadQuery(ReadAllQuery.java:464)
        at 
org.eclipse.persistence.queries.ObjectLevelReadQuery.executeDatabaseQuery(ObjectLevelReadQuery.java:997)
        at 
org.eclipse.persistence.queries.DatabaseQuery.execute(DatabaseQuery.java:675)
        at 
org.eclipse.persistence.queries.ObjectLevelReadQuery.execute(ObjectLevelReadQuery.java:958)
        at 
org.eclipse.persistence.queries.ReadAllQuery.execute(ReadAllQuery.java:432)
        at 
org.eclipse.persistence.queries.ObjectLevelReadQuery.executeInUnitOfWork(ObjectLevelReadQuery.java:1021)
        at 
org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.internalExecuteQuery(UnitOfWorkImpl.java:2898)
        at 
org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1225)
        at 
org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1207)
        at 
org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1181)
        at 
org.eclipse.persistence.internal.jpa.EJBQueryImpl.executeReadQuery(EJBQueryImpl.java:453)
        at 
org.eclipse.persistence.internal.jpa.EJBQueryImpl.getResultList(EJBQueryImpl.java:681)
        at overrides.Main.main(Main.java:138)
Java Result: 1

Line 138 is: List<ZenOrder> orders = q.getResultList();

I'm somewhat at a loss as what to try next. I would really like this 
work by creating a link from a column to a variable I've marked as 
transient. But at this point I'm just hoping I can get this to work 
somehow. :-)

--
Kind regards
Christian Michelsen