1. Introduction to JPA
Java Persistence API
Introduction to JPA

2. ORM Object-Relational Mapping
Problem
Object oriented programming languages
Relational DBMS
Several ORM frameworks has tried to ”fix” the problem
Example: Hibernate
JPA standardizes O/R mapping
Introduction to JPA

3. Impedance mismatch EJB 3 In Action, page 252
OO model
Relational model
Class, object
Table, row
Attributes
Columns
Identity
Primary key
Methods
Stored procedures
Inheritance
Not supported
Polymorphism
Introduction to JPA

4. Java EE 5 JPA is part of Java EE 5
JPA works between the Business Tier and the EIS tier (Enterprise Information System)
Figure from ”Java EE 5 Tutorial”
Introduction to JPA

5. Java EE 5 Some Java EE 5 containers GlassFish from Sun
Application Server from Oracle
JBoss
WebSphere from IBM
WebLogic from BEA
BEA was recently acquired by Oracle
Apache Tomcat
Not a full Java EE container, only a web container
Introduction to JPA

6. Java Persistence API JPA is an API Some persistence providers
Implemented by a persistence provider
Like JDBC is an API implemented by
Some persistence providers
Hibernate from JBoss
TopLink from Oracle
Kodo from BEA
recently acquired by Oracle
Introduction to JPA

7. The class EntityManager
EntityManager is the most important class of JPA
Full name javax.persistence.EntityManager
Some methods of EntityManager
T find(primaryKey)
Query createQuery(String jpql)
Creates a JPQL query
Query createNativeQuery(String sql)
Creates a SQL query
Some methods of Query
List getResultList()
Executes a Query and returns a list of objects
Introduction to JPA

8. Java Persistence Query Language (JPQL)
Very much like ordinary SQL
But not specific to any DBMS
JPA converts JPQL to ordinary SQL for the actual DBMS
Introduction to JPA

9. EJB 3 EJB 3 Enterprise Java Beans Important part of Java EE 5
Much simpler than EJB 2
POJO + annotations
Plain Old Java Objects
EJB classes can
Create database tables or
Be created from database tables
Introduction to JPA