Java Reference
In-Depth Information
ENTITIES
For the moment, the persistence unit declares one entity,
fancyfoods.persistence
.FoodImpl
.
FoodImpl
is an implementation of the
Food
interface we defined in sec-
tion 2.3.9. It allows
Food
objects to be persisted to, and read from, a database. The
nice thing about it, and the reason why so many people use
JPA
, is that it does all this
with one or two tiny little annotations;
JPA
does all the work for you, as shown in the
following listing.
Listing 3.3
The implementation of the
FoodImpl
entity class
@Entity(name = "FOOD")
public class FoodImpl implements Food {
Entity annotation declares JPA entity
@Id
private String name;
private double price;
private int quantity;
public FoodImpl() {
}
Primary key
No-argument
constructor for JPA
public FoodImpl(String name, double price, int quantity) {
this();
this.name = name;
this.price = price;
this.quantity = quantity;
With-argument
constructor for
convenience
}
@Override
public String getName() {
return this.name;
Getter and setter
for name column
}
public void setName(String name) {
this.name = name;
}
More getters
and setters
//...
Although it's too long to include in full here, the
FoodImpl
class is a thin data carrier.
It only contains getters and setters, without any business logic. It doesn't have respon-
sibility for persisting itself.
Enhancing the entities
Before they can be used by most
JPA
providers, entity
POJO
s must be
enhanced
.
Enhancement adds extra bytecode to the classes. If you're running in a Java
EE
5 (or
later) application server,
JPA
entities will be automatically enhanced. Usefully, recent
versions of Apache Aries are also able to perform this enhancement. If you aren't run-
ning in a system that provides automatic enhancement, then an Ant task (or similar)
can be used to enhance the entities when building, but it can also be done using an
Eclipse builder.
