On Oct 31, 2006, at 10:15 AM, Kevin Williams wrote:
You may have thought of this already but it would be good to
consider how SDO might play with this JPA integration.
I think it would be interesting to have the ability for SDO to handle
the "remoting" of JPA entities. For example, a service should be able
to retrieve entities using an EntityManager and pass those back to a
client. The databinding infrastructure in SCA would transparently
transform the entities into a form that the binding used to connect
the client to service could serialize out. If the client were an SCA
component, the serialization that came back could be transparently
converted to POJOs and merged with the JPA entities. What would be
nice is if the developer never has to generate classes or deal with
factories at all with the exception that entities passed over remote
boundaries implement Serializable (required by the JPA spec).
Something like
public class OrderServiceImpl implements OrderService {
@PersistenceContext(unitName = "orderDB")
protected EntityManager em;
// transaction semantics defined using SCA policy
Order getOrderById(String id) {
return entityManager.find(Order.class, id);
}
// transaction semantics defined using SCA policy
void updateOrder(Order order) throws OrderUpdateException{
return entityManager.merge(order);
}
}
public class ClientComponent {
@Reference
protected OrderService orderService;
public void updateOrder(.....){
Order order = orderService.getOrderById(orderNum);
// do something to the order
orderService.updateOrder(order);
}
}
The ClientComponent could be wired to OrderService over some remote
binding. SDO could be used in the client to only send back the delta
during the call to updateOrder(). If the binding were binary, I
imagine SDO could even forgo XML and use some optimized representation.
Patrick Linksey from OpenJPA mentioned to me a while back he would be
interested in providing an SDO wrapper over OpenJPA. This may be
something we want to look into once we get the JPA integration into
SCA working.
JIm
--
Kevin
Meeraj Kunnumpurath wrote:
Hi,
I have made a start on JPA integration. Haven't got to do much
because
of the build problems. The current home is
sca/services/persistence/common.
Anyway, this is a brief highlight of my thinking ...
1. Support injection of entity manager factory and entity manager
instances using PersistenceUnit and PersistenceContext annotations on
member fields.
2. For entity manager factory instances, the unitName attribute is
introspected at the component load time and scans all the available
persistence.xml for matching unit name.
3. The JPA provider API is used for creating the entity manager
factory.
4. Entity manager factory is caches somewhere (System composite)
5. This is then reused in all the components using the same
persistence
unit.
Persistence context is trickier. Entity manager AFAIK are thread
unsafe
and mostly bound to transactions. Hence, either we will have to proxy
this or use some sort of instance pooling and thread confinement
in our
component management. I think, proxying would be simpler. I plan
to get
at least the EMF side working by end of this week, if I can get the
build going.
Ta
Meeraj
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