jpa-hibernate-presentation

JPA and Hibernate
J. Slick
Computer Science Corp., General Dynamics Electric Boat
Jmslick@gmail.Com

JPA and Hibernate
Mid 90’s:
“Object/Relational Impedance Mismatch”

Impedance:
Restriction of flow between two systems

JPA and Hibernate

Relational model and Object model do not play well together

RELATIONAL OBJECT
Data Business Logic
Tables, Rows Objects, Collections
Identity / Sameness: PK Identity: a==b, a.equals(b)
Associate by FK Associate by Reference
Navigate by join Navigate object graph
No Inheritance Inheritance, Polymorphism
JDBC Data Types Java Types
Object / Relational Impedance Mismatch

Map business objects and associations to relational tables
Solution: Object / Relational Mapping

ORM Benefits?
 Productivity, fewer LOC
 Reduce time and tedious JDBC code
 Maintainability
 Focus on OO business logic
 Hide database architecture from user
 Transparently persist objects to tables
 Encourage OO queries
 Support native SQL queries
 Buffer changes between relational and object models
 Alterations
 Providers
 Data store

Map business objects and associations to relational tables
XML Metadata
<class name=”com.jpahib.Customer” table=”Customer”>
<property name=”username” type=string”/>
. . .
</class>
Annotated POJOs
@Entity
@Table(name=“CUSTOMER”)
public class Customer {
@Column(name=”USERNAME”)
private String username;
. . .
}
ORM

 Java spec for accessing, persisting Java objects to RDBMS
 Prompted by EJB 1 & 2
 Concepts from Hibernate, Oracle TopLink, JDO, EJB
 Finalized in EJB 3.0 spec, J2EE 5, 2006
 Just a specification, cannot perform persistence
 J2EE app servers should implement
 Can be used in Java EE and SE apps
 Many JPA implementations:
Hibernate, EclipseLink, OpenJPA, BEA Koda…
What is Java Persistence API?

Object/Relational Mapping tool to resolve Impedance
Mismatch
Persistence provider implementing JPA specification

What is Hibernate?

Hibernate Tools
• Ant command line
• Eclipse plug-in
• Wizards
• Config files
• Map files
• Reverse Engineering
• Code generation
• Editors: configs, queries
• HQL Console
• Query Editor
• SQL Analyze
• Visual Map Diagrams
• Code Hints, Completion

Hibernate Integration
Top Down: generate POJO’s from map file or DB
RDBMS
hbm2java
*.hbm.xml (Metadata)
. . .
</class>
@POJO @POJO

Hibernate Integration
Bottom up: generate schema from map file or POJOs
RDBMS
hbm2ddl
*.hbm.xml (Metadata)
. . .
</class>
@POJO @POJO

JPA Integration: Persistence Unit
 Specifies entity classes, queries, provider, connection
 Identified by name
 Injected by EE container or managed by SE application
<persistence>
<persistence-unit name=“pu1">
<provider>org.hibernate.ejb.HibernatePersistenceProvider</provider>
<mapping-file>META-INF/queries.xml</mapping-file>
<jar-file>packedEntity.jar</jar-file>
<class>com.jpahib.Customer</class>
<class>com.jpahib.Address</class>
<properties>
<property name=“javax.persistence.jdbc.driver”
value=“oracle.jdbc.driver.OracleDriver”/>
<property name="javax.persistence.jdbc.user"value="admin"/>
<property name="javax.persistence.jdbc.password"value="admin"/>
<property name=“hibernate.dialect"value=“Oracle10gDialect"/>
</properties>
</persistence-unit>
</persistence>

JPA Integration: Entity Manager
Container Managed (EE)
Persistence context propagated to application components
@PersistenceContext
EntityManager em;
em.find(), em.persist(T), em.remove(T), etc…
Application Managed (SE)
Persistence context from javax.persistence.Persistence
EntityManagerFactory emf = Persistence.createEntityManagerFactory(“pu1”);
EntityManager em = emf.createEntityManager();
em.find(), em.persist(T), em.remove(T), etc…

Insert
SQL / JDBC
String sql = "INSERT INTO CUSTOMER (USER_ID, USERNAME, ADDRESS) "
+ "VALUES(1, 'Joe Sixpack', '123 North St.')";
statement = dbConnection.createStatement();
statement.execute (sql);
JPA
Customer c = new Customer(1, “Joe Sixpack”, “123 North St.”);
entityManager.persist(c);

Read
SQL / JDBC
PreparedStatement ps = con.prepareStatement("select customer_id, name,
address, from customer");
ResultSet result = ps.executeQuery();
while(result.next()) {
Customer cust = new Customer();
cust.setCustomerID(result.getLong("customer_id"));
cust.setName(result.getString("name"));
cust.setAddress(result.getString("address"));
list.add(cust);
}
return list;
JPA
TypedQuery<Customer> q =
entityManager.createTypedQuery(“select * from customer”, Customer.class);
return q.getResultList();

Update
SQL / JDBC
String sql = "UPDATE CUSTOMER “
+ “SET USERNAME = ‘Ginger Vitys’, ADDRESS = ‘321 South St.’ “
+ “WHERE USER_ID = 1”;
JPA / Hibernate
Customer c = entityManager.find(Customer.class, 1);
c.setName(“Ginger Vitys”);
c.setAddress(“123 North South St.”);
entityManager.merge(c);

Delete
SQL / JDBC
String sql = "DELETE FROM CUSTOMER WHERE USER_ID = 1”;
JPA / Hibernate
Customer c = entityManager.find(Customer.class, 1);
entityManager.remove(c);

Case Study
• Port legacy FoxPro data to Oracle, optimize, export to JavaDB
• Write new Java web app
• Eight seasoned remote dev’s no JPA/Hibernate experience
• Single code base
• 217 Classes
• 153 Entities
• 107 Pages
• 96 Named queries
• Run application on shore (Oracle) and at sea (JavaDB)
• Oracle and JavaDB dialect differences
• Reduced functionality at sea, read-only DB, fewer pages
• Change persistence unit with single word: “shore” or “boat”

jpa-hibernate-presentation

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