Implementing POJOs with EJB 3 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 367

makes an entity bean persistent, remove() deletes an entity bean, and find()
retrieves an entity bean by its primary key.
The Query interface is equivalent to the Hibernate or JDO Query interfaces. It
defines methods for executing queries, bulk deletes, and bulk updates. An appli-
cation creates a Query by calling factory methods defined by the EntityManager
such as createQuery() , which creates a Query from a query string, and create-
NamedQuery() , which creates one from a named query. The Query interface defines
several methods, including setParameter() , which sets a query parameter; get-
ResultList() , which executes a query and returns a list of results; and execute-
Update() , which executes an update or delete statement. For example, here is a
code fragment that shows how an application can execute an EJB 3 named query:
EntityManager entityManager = …;
Query query = entityManager
.createNamedQuery("Restaurant.findAvailableRestaurants");
…
query.setParameter("dayOfWeek", new Integer(dayOfWeek));
query.setParameter("hour", new Integer(hour));
query.setParameter("minute", new Integer(minute));
query.setParameter("zipCode", new Integer(zipCode));
List result = query.getResultList();
The application calls EntityManager.createNamedQuery() to create the query, sets
some parameters, and executes the query by calling Query.getResultList() .
The EntityManagerFactory interface is equivalent to a Hibernate Session-
Factory or a JDO PersistenceManagerFactory . It has a createEntityManager()
method that creates an EntityManager . J2EE applications will typically use depen-
dency injection to access an EntityManager , but client-side code, most notably test
cases, needs to explicitly create an EntityManager using the EntityManager-
Factory . Client-side code creates an EntityManagerFactory by calling Persis-
tence.createEntityManagerFactory() , which is a static method.
The EntityTransaction interface is equivalent to the Transaction interfaces
provided by Hibernate and JDO . The application gets the EntityTransaction
from the EntityManager and calls its methods to control transactions. J2EE appli-
cations will most likely use container-managed transactions, but client-side tests
will use EntityTransaction .
As you can see, the EJB 3 persistence interface is completely different from the
EJB 2 equivalent. It's very similar to JDO and Hibernate API s. Later in this chapter,
you will see examples of how to use it. Let's now look at EJB 3 detached objects.