Working with Entity bean using JPA

to persist the data in the database. The Database Model is called the Domain Model that represents the persistence objects or entities in the database. An entity may be a person, place or a thing about which you want
to store the data in the database. A rich domain model includes the characteristics of all the object-oriented behavior like inheritance, polymorphism and many more.

Lets read about the some common annotations that are used to develop a JPA application.

Primary Key Generation:

In EJB 3.0, a primary key is used with @Id annotation. Depending upon the application requirement, Id annotation can be used with different primary key generation strategies defined by GeneratorType enum. The GeneratorTypes are TABLE, SEQUENCE, IDENTITY, AUTO, and NONE.

Declaring an entity bean:

Every bound persistent POJO class is an entity bean and is declared using the @Entity annotation (at the class level). @Entity declares the class as an entity bean (i.e. a persistent POJO class), which tells the EJB3 container that this class needs to be mapped to a relational
database table.

Defining the table:
@Table is set at the class level; it allows you to define the table, catalog, and schema names for your entity bean mapping. If no @Table is defined the default values are used, that is the unqualified class name of the

Here is the sample code using of these annotations:

@SequenceGenerator(name =
“book_sequence”, sequenceName =
public class Book implements Serializable {
Long empid;


public Long getId()
{ return id; }
public void setId(Long id)
{ = id; }

The @Table defines the table name. Each instance of the entity bean represents a row of data in the table. Each column in the table corresponds to a data attribute in the entity bean. The @SequenceGenerator defines a sequence generator. A sequence is a database feature. It returns the next Integer or Long value each time it is called.

@Id declares the identifier property of this entity bean. @GeneratedValue annotation indicates that the server automatically generates the primary key value.

Managing Entities:

The entity manager manages entities. The entity manager is represented by javax.persistence.EntityManager instances. Each EntityManager instance is associated with a persistence context.

A persistence context defines the scope under which particular entity instances are created, persisted, and removed. It is a set of managed entity instances that exist in a particular data store. The EntityManager interface defines the methods that are used to interact with the
persistence context.

The EntityManager Interface:

The EntityManager API creates and removes persistent entity instances, finds entities by the entity’s primary key, and allows queries to be run on entities. To obtain an EntityManager instance, inject the entity manager into the
application component:

EntityManager em;
Feb 2008 | Java Jazz Up | 8
View All Topics
All Pages of this Issue
Pages: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,

, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53 , 54, 55, 56, 57,

, 59, 60, 61, 62, 63 , 64, 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ,

Download PDF