JPA2 - a brief intro

JPA2 BRIEF INTRO
by Tiziano Lattisi

mercoledì 13 febbraio 13

WHAT IS JPA2

Java Persistence API

JPA2 in Java EE 6 (JPA1 in Java EE 5)

It’s a O/RM (Object Relational Mapping)

Framework to provide persistence

An object is a row in a master table (...)


AND...

annotation || XML descriptor (configuration by exception)

POJO (Plain Old Java Object) based

Outside container (no server required)

No Bean interface required (no implements Serializable)

Different persistence providers (Hibernate, EclipseLink, ...)


CASE STUDY: LIBRARY

The library contains several books

The library can loan one or more books to a person

Actors: Library, Book, Person, Loan


O/RM
public class Person {
private Long id; PERSON
private String name;
PK ID
private String surname;
private Date birthday;
? NAME
private Collection<Loan> loanCollection;
SURNAME
public Person() {} GENRE
/* accessor methods */
} LOAN
public class Loan { PK ID
private Long id; FROMDATE
private Date fromdate;
private Date todate; TODATE
private Person person; FK PERSON
private Book book;
FK BOOK
public Loan(){ }
}
BOOK
public class Book { PK ID
private Long id;
private String title; TITLE
private String description; DESCRIPTION
public Book(){ } GENRE
}


O/RM

to map variables to database columns

to handle data types between database and Java

to map tables references in relationship between objects

to manage the cycle of life of the object


PERSISTENCE.XML
<?xml version="1.0" encoding="UTF-8"?>

<persistence version="2.0" xmlns:xsi="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://
java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

<persistence-unit name="DemoPU" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:demo"/>
<property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
<property name="javax.persistence.jdbc.user" value=""/>
<property name="javax.persistence.jdbc.password" value=""/>
<property name="eclipselink.ddl-generation" value="create-tables"/>
</properties>
<class>com.axiastudio.pypapi.demo.entities.Book</class>
<class>com.axiastudio.pypapi.demo.entities.Loan</class>
<class>com.axiastudio.pypapi.demo.entities.Person</class>
</persistence-unit>

</persistence>


IDE HELPS US

example:

PU setup in
Netbeans 7.2 IDE


BY ANNOTATION
@Entity
@Table(name = "person")
public class Person implements Serializable {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name = "id")
private Long id;

@Column(name = "name")
private String name;

@Column(name = "surname")
private String surname;

@Column(name = "birthday")
@Temporal(TemporalType.DATE)
private Date birthday;

@OneToMany(mappedBy = "person", orphanRemoval = true, cascade=CascadeType.ALL)
private Collection<Loan> loanCollection;

public Person() { }
/* accessor methods */
}


BY XML DESCRIPTOR

<entity-mappings>
...
<entity class="com.axiastudio.pypapi.demo.entities.Person"
metadata-complete="true">
<table-name="PERSON"/>
<attributes>
<id name="id"/>
<id name="name"/>
<id name="surname"/>
<id name="birthday"/>
<id name="id"/>
</attributes>
</entity>
</entity-mappings>


SEQUENCE

by annotation
@SequenceGenerator(name="genBook", sequenceName="book.book_id_seq",
initialValue=1, allocationSize=1)

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator="genBook")
private Long id;

by descriptor
<id name="id">
<generated-value strategy="SEQUENCE" generator="genBook"/>
<sequence-generator name="genBook" sequence-name="book.book_id_seq"/>
</id>


INSERT

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import com.axiastudio.pypapi.demo.entities.Book;
import com.axiastudio.pypapi.demo.entities.Genre;

EntityManagerFactory emf = Persistence.createEntityManagerFactory("DemoPU");
em = emf.createEntityManager();

Book book = new Book();
book.setTitle("Dubliners");
book.setDescription("a collection of 15 short stories");
book.setGenre(Genre.ROMANCE);

em.getTransaction().begin();
em.persist(book);
em.getTransaction().commit();


SELECT
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Book> cq = cb.createQuery(Book.class);
TypedQuery<Book> tq = em.createQuery(cq);
List<Book> books = tq.getResultList();

for( Book book: books ){
switch (book.getDescription()) {

case "Anna Karenina":
assert "ROMANCE".equals(book.getGenre().toString());
break;

case "Pro JPA":
assert "REFERENCE".equals(book.getGenre().toString());
break;

}
}
}


SELECT (CRITERIA)

CriteriaQuery<Book> cq = cb.createQuery(Book.class);

Root from = cq.from(Book.class);
// from.get("description")
Predicate predicate = cb.like(from.get(Book_.description), "%very%");
cq = cq.where(predicate);

TypedQuery<Book> tq = em.createQuery(cq);

List<Book> books = tq.getResultList();
assert books.size() == 1;
assert "Anna Karenina".equals(books.get(0).getTitle());

Book book = tq.getSingleResult();
assert "Anna Karenina".equals(book.getTitle());


UPDATE
CriteriaQuery<Person> cq = cb.createQuery(Person.class);
Root from = cq.from(Person.class);
cq = cq.where(cb.and(cb.equal(from.get(Person_.name), "Tiziano"),
cb.equal(from.get(Person_.surname), "Lattisi")));
TypedQuery<Person> tq = em.createQuery(cq);
Person person = tq.getSingleResult();

assert "Tiziano".equals(person.getName()); assert person.getEmail() == null;
Long key = person.getId();
person.setEmail("tiziano.lattisi@gmail.com");

Person personByKey = em.find(Person.class, key);
assert "tiziano.lattisi@gmail.com".equals(personByKey.getEmail());

em.detach(person);
person = em.find(Person.class, key);
assert ! "tiziano.lattisi@gmail.com".equals(person.getEmail());

person.setEmail("tiziano.lattisi@gmail.com");
em.getTransaction().begin(); em.merge(person); em.getTransaction().commit();
Person personByKey2 = em.find(Person.class, key);
assert "tiziano.lattisi@gmail.com".equals(personByKey2.getEmail());


DELETE
Person person = new Person();
person("Tiziano");
person("Lattisi");

em.persist(person);
Long aPrimaryKey = person.getId();

[...]

Person person = em.find(Person.class, aPrimaryKey);

em.remove(person);

person = em.find(Person.class, aPrimaryKey);
assert person == null;


AND NOW...

Thank you.

Tiziano Lattisi

Me: http://www.linkedin.com/in/tizianolattisi/
Slides: http://www.slideshare.net/lattisi/
Examples: http://tinyurl.com/crn3wwq


JPA2 - a brief intro

More Related Content

What's hot (18)

Viewers also liked (9)

Similar to JPA2 - a brief intro (20)

More from Tiziano Lattisi (6)

JPA2 - a brief intro