The EJB container determines the persistent properties by looking for all getter/setter method pairs. By default, all getter/setter methods will be treated as persistence properties.
Defining an Entity is easy. First, tag the class as an @Entity. In the minimum, you must at least define a primary key field using the @Id annotation.
@Id @GeneratedValue
public int getId()
{
return id;
}
Annotations must be defined on the getter method. The above @Id annotation tells the container that id is the primary key property. The @GeneratedValue: that it should be automatically generated by the container.
Also, the create table name is specified using the @Table annotation
@Table(name = "PURCHASE_ORDER")
If the table name isn't specified it defaults to the bean name of the class. For instance, the LineItem EJB would be mapped to the LINEITEM table.
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy="order")
public Collection<LineItem> getLineItems()
{
return lineItems;
}
Generics must be used so that the container can determine the bean order is related to.
CascadeType.ALL specifies that when an Order is created, any LineItems held in the lineItems collection will be created as well (CascadeType.PERSIST). If the Order is delete from persistence storage, all related LineItems will be deleted (CascadeType.REMOVE). If an Order instance is reattached to persistence storage, any changes to the LineItems collection will be merged with persistence storage (CascadeType.MERGE).
FetchType.EAGER specifies that when the Order is loaded whether or not to prefetch the relationship as well. If you want the LineItems to be loaded on demand, then specify FetchType.LAZY.
The mappedBy attribute specifies that this is a bi-directional relationship that is managed by the order property on the LineItem entity bean.
@ManyToOne
@JoinColumn(name = "order_id")
public Order getOrder()
{
return order;
}
The @JoinColumn specifies the foreign key column within the LineItem table.
The EntityManager service is injected using field injection and the @PersistenceContext annotation.
@PersistenceContext private EntityManager manager;
The EntityManager is central to EJB 3.0 as there are no homes. The EntityManager is used to do querying, creating, find by primary key, and removal of entity beans.
Unix: $ export JBOSS_HOME=<where your jboss 4.0 distribution is>
Windows: $ set JBOSS_HOME=<where your jboss 4.0 distribution is>
$ ant
$ ant run
run:
[java] Buying 2 memory sticks
[java] 2004-10-06 22:12:44,131 INFO org.jboss.remoting.InvokerRegistry[main] - Failed to load soap remoting transpo
rt: org/apache/axis/AxisFault
[java] Buying a laptop
[java] Print cart:
[java] Total: $3000.0
[java] 2 Memory stick 1000.0
[java] 1 Laptop 2000.0
[java] Checkout
The INFO message you can ignore. It will be fixed in later releases of JBoss 4.0.