Implementing POJOs with EJB 3 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 364

@Entity(access=AccessType.FIELD)
class PendingOrder {
@Id(generate = GeneratorType.AUTO)
private int id;
private int state = PendingOrder.NEW;
@ManyToOne
private Restaurant restaurant;
@OneToMany(cascade = CascadeType.ALL)
private List<PendingOrderLineItem> lineItems
= new ArrayList<PendingOrderLineItem>();
@ManyToOne
private Coupon coupon;
…
The @Entity annotation specifies that the PendingOrder class is an entity bean,
and the access=AccessType.FIELD member tells the EJB container to map its fields
rather than its properties to the database. The @Id annotation identifies the pri-
mary key field and tells the EJB container to generate a primary key. The @OneTo-
Many annotation specifies that the lineItems field is a one-to-many relationship,
and the @ManyToOne annotation specifies that the restaurant and coupon fields are
many-to-one relationships. The EJB 3 persistence mechanism uses the information
specified by the annotations in the same way that the JDO or Hibernate imple-
mentation uses the XML O/R mapping documents.
This example uses the default EJB 3 O/R mapping rules that generate default
table and column names and define the mappings for relationships. The
PendingOrder class is mapped to the PENDINGORDER table, the id field is
mapped to the ID column, and the lineItems field is mapped to a join table
called PENDING_ORDER_PENDING_ORDER_LINE_ITEM , which has foreign keys
to the PENDINGORDER and PENDINGORDERLINEITEM tables. You can, however,
use annotations to specify the names of the tables and columns and change how
some relationships are mapped. Later in this chapter you'll see examples of how
to do that.
EJB 3 encourages developers to use annotations to define an EJB , but you can
still use XML deployment descriptors. Whether you use annotations or deploy-
ment descriptors is largely a matter of personal preference, but there are situa-
tions in which deployment descriptors are useful. For example, the annotations
that define the O/R mapping can be verbose, and it can be easier to use a deploy-
ment descriptor instead. Another potential use for a deployment descriptor is to