Implementing POJOs with EJB 3 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 366

A standardized O/R mapping mechanism

■

Support for inheritance

■

Embedded objects whose fields are mapped to the same table as the entity
bean's fields

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Optimistic locking with version numbers

■

EJB 3 also enhances the EJB query language with new features such as Hibernate-
style fetch joins for eagerly loading objects and bulk update and delete. In addi-
tion, queries can be defined either statically or generated dynamically.

Improved persistence API
As I mentioned earlier, EJB 3 has a new and improved persistence API that is quite
similar to the API s provided by JDO and Hibernate. As figure 10.1 shows, the API
consists of interfaces that play the role of connection factory, connection, transac-
tion, and query. There is also a Persistence class that provides methods for creat-
ing the EJB 3 equivalent of the connection factory.
The EntityManager replaces the entity bean home interfaces and is equivalent
to the JDO PersistenceManager and Hibernate Session . It defines methods for
creating, deleting, and querying entity beans. For example, the create() method

Persistence

createEntityManagerFactory() {static}
...

<<creates>>

EntityManager
Factory

createEntityManager()
close()
...

<<creates>>

<<interface>>
EntityManager

Entity
Transaction

<<interface>>
Query

create()
remove()
find()
Query createQuery()
Query createNamedQuery()
EntityTransaction
getTransaction()
...

<<creates>>

<<creates>>

begin()
commit()
rollback()
...

setParameter()
List getResultList()
executeUpdate()
...

Figure 10.1 The EJB 3 persistence API