Difference between revisions of "EclipseLink/Examples/SDO/JPA"

Revision as of 14:16, 30 January 2009

Overview

In this use case a developer wishes to expose their JPA model as an SDO DataObject model (static or dynamic). The JPA entities are mapped to a XSD through JAXB mappings.

1. In this use case the developer defines the mapping from the JPA domain model (POJOs) to an XML schema (XSD) using JAXB mappings (annotations or EclipseLink native OXM).
2. The XSD is then generated using the JAXB Java-XML Compiler (JXC), or in the meet-in-the-middle case the schema from the previous step.
3. The SDO Data Object model is now implicitly define through the use of the generated XSD. If the service developer wishes to use a static DataObject model they can optionally use the SDO compiler to generate this model based on the XSD.

SDO Bootstrapping

When the application needs to interact with the JPA backed SDO model the service being developed must bootstrap the SDO context. In general SDO usage the context is initialized using something like:

JAXBContext jaxbContext = JAXBContext.newInstance("com.example.customer");
JAXBHelperContext jaxbHelperContext = new JAXBHelperConext(jaxbContext);
jaxbHelperContext.getXSDHelper().define(customerXSD);

When using JPA entities behind the SDO model the service developer will need to express the XML schema represenation through JAXB mappings (including MOXy extensions) on the JPA entities.

For more informations see:

Querying

When developing a service that will return SDO DataObject instances from the relational database the developer will issue queries against the database using JPA (PK Find, JP QL or Native ORM queries in JPA 1.0). The resulting entities will then be wrapped by DataObject using a provided helper class.

EntityManagerFactory emf = Persistence.createEntityManagerFactory("CustomerExample");      
EntityManager em = emf.createEntityManager();
List<MyEntity> entities = em.createQuery("SELECT e FROM MyEntity e WHERE ...").getResultList();
 
List<DataObject> dataObjects = jaxbHelperContext.wrap(entities);

Creating (JPA persist)

Creating new entities in the database can be done by explicitly requesting the new data to be persisted. If the DataObject being persisted combines new objects with updates to existing objects then the Updating scenario below will be used.

EntityManagerFactory emf = Persistence.createEntityManagerFactory("CustomerExample");      
EntityManager em = emf.createEntityManager();
 
JAXBContext jaxbContext = JAXBContext.newInstance("com.example.customer");
JAXBHelperContext jaxbHelperContext = new JAXBHelperConext(jaxbContext);
jaxbHelperContext.getXSDHelper().define(customerXSD);
 
Type customerType = jaxbHelperContext.getType(Customer.class);
DataObject customerDO = jaxbHelperContext.getDataFactory().create(customerType);
customerDO.setString("firstName", "Jane");
customerDO.setString("lastName", "Doe");
DataObject addressDO customerDO.create("address");
addressDO.setString("street", "123 Any Street");
addressDO.setString("city", "Any Town");
 
em.getTransaction().begin();
em.persist(jaxbHelperContext.unwrap(customerDO));
em.getTransaction().commit();

Note: The cascade persist configuration on the underlying entity's relationship mappings will define the scope of which new instances in the graph will be persisted.

Updating (JPA merge)

In the case of updates to existing entities as well as addition of new entities through relationships the merge call on the helper will be used.

EntityManagerFactory emf = Persistence.createEntityManagerFactory("CustomerExample");      
EntityManager em = emf.createEntityManager();
 
JAXBContext jaxbContext = JAXBContext.newInstance("com.example.customer");
JAXBHelperContext jaxbHelperContext = new JAXBHelperConext(jaxbContext);
jaxbHelperContext.getXSDHelper().define(customerXSD);
 
em.getTransaction().begin();
em.merge(jaxbHelperContext.unwrap(dataObject));
// ... Other operations within the same TX
em.getTransaction().commit();

Note: The creation of new objects and the removal of existing objects in the graph result in database operations based on the cascade and private-owned configurations in the JPA model's relationship mappings.

Deleting (JPA remove)

Entities can be removed from the database using the helper's remove call:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("CustomerExample");      
EntityManager em = emf.createEntityManager();
 
JAXBContext jaxbContext = JAXBContext.newInstance("com.example.customer");
JAXBHelperContext jaxbHelperContext = new JAXBHelperConext(jaxbContext);
jaxbHelperContext.getXSDHelper().define(customerXSD);
 
em.getTransaction().begin();
em.remove(jaxbHelperContext.unwrap(dataObject));
em.getTransaction().commit();