topic : jpa kaster nurmukan. overview of jpa entitymanager

Topic : JPAKaster Nurmukan

• Overview of JPA

• EntityManager

• O/R Mapping• Primary entity annotations• EntityManager• Entity Relationships• Practice

Database TablePOJO

Forward Engineering

Reverse Engineering

Java Persistence API

• Java Persistence API (JPA)– Annotations for object-relational mapping

– Data access API

– An object-oriented query language JPQL

• Hibernate– The most popular Java ORM library

– An implementation of JPA

• Hibernate without JPA– API: SessionFactory, Session, Query, Transaction

– More features

• Hibernate with JPA– API: EntityManagerFactory, EntityManager, Query, Transaction

– Better portability– Behaviors are better defined and documented

• Java classes– Employee.java

• JPA configuration file– persistence.xml

• Code to access the persistent objects– EmployeeTest.java

• (Optional) Logging configuration files– log4j.properties

• Plain Java classes (POJOs); however, it is recommended that– Each persistent class has an identity field

– Each persistent class implements the Serializable interface

– Each persistent field has a pair of getter and setter, which don’t have to be public

• @Entity. Mark class as an entity• @Id. Define primary key• @EmbeddedId. Define composite key• @Table(name=“TABLE_NAME”). Define table

name for entity class. • @Column. Define column property.• @Transient. Ignored by persistence framework.• @GeneratedValue,@SequenceGenerator.

Autopopulate column with sequence generator.

• Maintains a cache of instances within a transactional context (persistence context)

• We can acquire EntityManager instance using :Dependency InjectionEntityManagerFactoryJNDI Lookup

• Operations : persist(), merge(), remove(), find(), createNamedQuery(), createQuery()

• Persistence unit is declared in persistence.xml

• @OneToOne. One to One is represented by a single-value entity reference at one or both ends of the relationship

• @OneToMany. This annotation is added to a Collection relationship field.

• @ManyToOne. Indicating that is an entity is part of a Collection

• @ManyToMany. This annotation is assigned to a Collection relationship field to indicate the target entity also has a Collection of the source entity type.

• Lazy vs Eager Binding• Cascade (ALL, PERSIST, MERGE, REMOVE, REFRESH)

v110912 Java Persistence: EntityManager 12

javax.persistence.EntityManager• Replaces much of the EJB 2.x “Home”

functionality• Handles O/R Mapping of Entities to the

database• Provides APIs

– inserting objects into database– getting objects from database– synchronizing objects with database– querying database

• Provides caching• Coordinates with transactional services (JTA)• Tightly integrated with Java EE and EJB, but

not limited to that environment


javax.persistence.EntityManager• Replaces much of the EJB 2.x “Home”

functionality• Handles O/R Mapping of Entities to the database• Provides APIs

– inserting objects into database– getting objects from database– synchronizing objects with database– querying database

• Provides caching• Coordinates with transactional services (JTA)

– Tightly integrated with Java EE and EJB, but not limited to that environment


Entities

• (formerly and sometimes still called Entity Beans)

• are now Plain Old Java Objects (POJOs)– nothing special happens when calling new

Author author = new Author();

• are not persistent until associated with an EntityManager

em.persist(author);


Example Author POJO [email protected] class Author { private long id; private long version=0; private String firstName; private String lastName; private String subject; private Date publishDate; public Author() {} public Author(long id) { this.id = id; } @Id @GeneratedValue public long getId() { return id;} private void setId(long id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } ... }

Warning: Using GeneratedValue without specifying a specific strategy should only be used when you have no intention of controlling how the provider manages primary keys for this object type. This would be rare.


Creating Entity in DatabaseAuthor author = new Author(); //primary key will be genauthor.setFirstName("dr");author.setLastName("seuss");author.setSubject("children");author.setPublishDate(new Date());

log_.info("creating author:" + author);em.persist(author);log_.info("created author:" + author);

//output-creating author:id=0, fn=dr, ln=seuss, subject=children,

pdate=Fri Sep 15 11:54:15 EDT 2006-created author:id=50, fn=dr, ln=seuss, subject=children,

pdate=Fri Sep 15 11:54:15 EDT 2006


Managed and Unmanaged Entities

• Unmanaged state (detached)– instance not associated with an EntityManager– state changes are not tracked– can be serialized to client and returned to be

synchronized with database– nothing equivalent to this state in EJB 2.1 entity beans

• Managed state (attached)– instance associated with an EntityManager– state changes are tracked within a Persistence

Context– EJB 2.1 entity beans were always managed

• client interfaced with data through a proxy or state transferred through a Data Transfer Object


Persistence Context

• A set of attached entity instances managed by an EntityManager

• All entities become detached once closed• Two types

– Transaction-scoped Persistence Contexts• begin/end at transaction boundaries• only made available through container managed

persistence contexts– Extended Persistence Contexts

• live beyond any single transaction• allow longer-lived interactions with database without

lengthy transactions tying up database resources

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Persistence Context Examples

• Transaction-scoped (inside server container)@PersistenceContext(unitName=”jpaDemo”)

EntityManager em;@TransactionAttribute(REQUIRED)public void update(long authorId, String type) {

Author author = em.find(Author.class, authorId);author.setType(type);

}

• Extended (inside or outside server container)EntityManager em = Persistence. createEntityManagerFactory(“jpaDemo”).createEntityManager();tx.begin(); //tx 1 beginsAuthor author = em.find(Author.class, authorId);tx.commit(); //tx 1 ends, but author remains managed...tx.begin(); //tx 2 beginsauthor.setType(type);tx.commit(); //tx 2 ends, and author is still managed until close

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Persistence Unit

• A set of classes that are mapped to the database

• defined in META-INF/persistence.xml • must have an identity

– “” is a valid identity• Classes

– may be named in persistence.xml file– may be automatically scanned for in the classpath

• orm.xml– optionally provided to augment, provide, or replace

class persistence metadata– (more on orm.xml in Core ORM topic)


Example Component Layout META-INF/ +---persistence.xmlejava + ---examples +---… +---DAOException.class +---AuthorDAO.class +---jpa | +---JPAAuthorDAO.class | +---JPADAOBase.class +--domain +---Author.class

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Example persistence.xml<?xml version="1.0" encoding="UTF-8"?><persistence xmlns="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_1_0.xsd" version="1.0">

<persistence-unit name="jpaDemo">

<jta-data-source>java:/ejavaDS</jta-data-source>

<properties> <property name="hibernate.hbm2ddl.auto" value="create"/> <property name="hibernate.show_sql" value="true"/ </properties> </persistence-unit> </persistence>

referenced by name

• global JNDI name by which provider references resource(will be used when deployed within server)• may use properties element in Java SE environments that lack JNDI

• vendor-specific way to configure persistence provider


Another Example persistence.xml<?xml version="1.0" encoding="UTF-8"?><persistence xmlns="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_1_0.xsd" version="1.0">

<persistence-unit name="jpaDemo">

<provider>org.hibernate.ejb.HibernatePersistence</provider>

<properties> <property name="hibernate.cache.provider_class" value="net.sf.ehcache.hibernate.Provider"/> <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/> <property name="hibernate.connection.url" value="jdbc:hsqldb:hsql://localhost:9001"/> <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/> <property name="hibernate.connection.password" value=""/> <property name="hibernate.connection.username" value="sa"/> <property name="hibernate.show_sql" value="false"/> <property name="hibernate.hbm2ddl.auto" value="create"/> </properties> </persistence-unit>

</persistence

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persistence.xml elements• name – identity to reference Persistence Unit• provider – fully qualified name of javax.persistence.PersistenceProvider

– not needed if provider found in classpath acceptable• mapping-file – resource path to optional mapping file

– can be used to specify <class>es or specify/override @Annotation details• jta-data-source

– vendor-specific reference to data source using JTA transactions• non-jta-data-source

– vendor-specific reference to data source using RESOURCE_LOCAL transactions

• jar-file– optional/additional jar file to scan for classes

• class– specifies entity classes not automatically scanned by provider

• exclude-unlisted-classes– if set, provider will not automatically scan archive for entity classes

• properties– may be used to provide vendor-specific properties to configure persistence

providers

25

Java SE Steps

• Startup– Get EntityManagerFactory

• Runtime– Create EntityManager– Start Transaction– Interact with Entity Manager– Commit Transaction– Close EntityManager

• Shutdown– Close EntityManagerFactory

26

updating entities• Updates to managed entities automatically

get propagated to database according to flush policy public Author update(Author author) { Author dbAuthor = em.find(Author.class,author.getId());

dbAuthor.setFirstName(author.getFirstName()); dbAuthor.setLastName(author.getLastName()); dbAuthor.setSubject(author.getSubject()); dbAuthor.setPublishDate(author.getPublishDate()); return dbAuthor;}

– Note that if author passed in was already managed...• the changes have already been queued• the dbAuthor returned from the find() will be the same object as author• the sets are unnecessarily changing the values of the Author to their current

values


(optional!)Potential Utiltity Classpackage ejava.examples.dao.jpa;

import java.util.HashMap;import java.util.Map;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;

public class JPAUtil { private static final Map<String, EntityManagerFactory> factories = new HashMap<String, EntityManagerFactory>(); public static EntityManagerFactory getEntityManagerFactory(String puName) { EntityManagerFactory emf = factories.get(puName); if (emf == null) { synchronized(factories) { emf = factories.get(puName); if (emf == null) { emf = Persistence.createEntityManagerFactory(puName); factories.put(puName, emf); } } } return emf; } public static void close() { synchronized(factories) { for(String puName : factories.keySet()) { factories.get(puName).close(); } factories.clear(); } }}

• http://www.oracle.com

IndicThreads.com Java Meet June 2006

http://www.oracle.com/

topic : jpa kaster nurmukan. overview of jpa entitymanager

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