openjpa-project/src/doc/manual/jpa_overview_arch.xml - openjpa - Git at Google

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 <chapter id="jpa_overview_arch">
     <title>
         Java Persistence API Architecture
     </title>
     <indexterm zone="jpa_overview_arch">
         <primary>
             JPA
         </primary>
         <secondary>
             architecture
         </secondary>
     </indexterm>
     <para>
 The diagram below illustrates the relationships between the primary components
 of the JPA architecture.
     </para>
     <mediaobject>
         <imageobject>
             <!-- PNG image data 400 x 256 (see README) -->
             <imagedata fileref="img/jpa-arch.png" width="267px"/>

         </imageobject>
         <textobject>
             <phrase>
                 JPA architecture
             </phrase>
         </textobject>
     </mediaobject>
     <note>
         <para>
 A number of the depicted interfaces are only required outside of an
 EJB3-compliant application server. In an application server, <classname>
 EntityManager</classname> instances are typically injected, rendering the
 <classname>EntityManagerFactory</classname> unnecessary. Also, transactions
 within an application server are handled using standard application server
 transaction controls. Thus, the <classname>EntityTransaction</classname> also
 goes unused.
         </para>
     </note>
     <itemizedlist>
         <listitem>
             <para>
             <indexterm>
                 <primary>
                     Persistence
                 </primary>
             </indexterm>
 <emphasis role="bold"><link linkend="jpa_overview_persistence"><classname>
 Persistence</classname></link></emphasis>: The <classname>
 javax.persistence.Persistence</classname> class contains static helper methods
 to obtain <classname>EntityManagerFactory</classname> instances in a
 vendor-neutral fashion.
             </para>
         </listitem>
         <listitem>
             <para>
             <indexterm>
                 <primary>
                     EntityManagerFactory
                 </primary>
             </indexterm>
 <emphasis role="bold"><link linkend="jpa_overview_emfactory"><classname>
 EntityManagerFactory</classname></link></emphasis>: The <classname>
 javax.persistence.EntityManagerFactory</classname> class is a factory for
 <classname> EntityManager</classname> s.
             </para>
         </listitem>
         <listitem>
             <para>
             <indexterm>
                 <primary>
                     EntityManager
                 </primary>
             </indexterm>
 <emphasis role="bold"><link linkend="jpa_overview_em"><classname>EntityManager
 </classname></link></emphasis>: The <classname>javax.persistence.EntityManager
 </classname> is the primary JPA interface used by applications. Each
 <classname>EntityManager</classname> manages a set of persistent objects, and
 has APIs to insert new objects and delete existing ones. When used outside the
 container, there is a one-to-one relationship between an <classname>
 EntityManager</classname> and an <classname> EntityTransaction</classname>.
 <classname> EntityManager</classname>s also act as factories for <classname>
 Query</classname> instances.
             </para>
         </listitem>
         <listitem>
             <para>
             <indexterm>
                 <primary>
                     entity
                 </primary>
             </indexterm>
 <emphasis role="bold"><link linkend="jpa_overview_pc"><classname>Entity
 </classname></link></emphasis>: Entites are persistent objects that represent
 datastore records.
             </para>
         </listitem>
         <listitem>
             <para>
             <indexterm>
                 <primary>
                     EntityTransaction
                 </primary>
             </indexterm>
 <emphasis role="bold"><link linkend="jpa_overview_trans"><classname>
 EntityTransaction</classname></link></emphasis>: Each <classname>EntityManager
 </classname> has a one-to-one relation with a single <classname>
 javax.persistence.EntityTransaction</classname>. <classname>
 EntityTransaction</classname>s allow operations on persistent data to be
 grouped into units of work that either completely succeed or completely fail,
 leaving the datastore in its original state. These all-or-nothing operations
 are important for maintaining data integrity.
             </para>
         </listitem>
         <listitem>
             <para>
             <indexterm>
                 <primary>
                     Query
                 </primary>
             </indexterm>
             <indexterm>
                 <primary>
                     Java Persistence Query Language
                 </primary>
                 <see>
                     JPQL
                 </see>
             </indexterm>
             <indexterm>
                 <primary>
                     JPQL
                 </primary>
             </indexterm>
             <indexterm>
                 <primary>
                     JPA
                 </primary>
                 <secondary>
                     query language
                 </secondary>
                 <see>
                     JPQL
                 </see>
             </indexterm>
             <indexterm>
                 <primary>
                     Structured Query Language
                 </primary>
                 <see>
                     SQL
                 </see>
             </indexterm>
             <indexterm>
                 <primary>
                     SQL
                 </primary>
             </indexterm>
 <emphasis role="bold"><link linkend="jpa_overview_query"><classname>Query
 </classname></link></emphasis>: The <classname>javax.persistence.Query
 </classname> interface is implemented by each JPA vendor to find persistent
 objects that meet certain criteria. JPA standardizes support for queries using
 both the Java Persistence Query Language (JPQL) and the Structured Query
 Language (SQL). You obtain <classname>Query</classname> instances from an
 <classname>EntityManager</classname>.
             </para>
         </listitem>
     </itemizedlist>
     <para>
 The example below illustrates how the JPA interfaces interact to execute a JPQL
 query and update persistent objects. The example assumes execution outside a
 container.
     </para>
     <example id="jpa_overview_arch_interact_outside">
         <title>
             Interaction of Interfaces Outside Container
         </title>
 <programlisting>
 // get an EntityManagerFactory using the Persistence class; typically
 // the factory is cached for easy repeated use
 EntityManagerFactory factory = Persistence.createEntityManagerFactory(null);

 // get an EntityManager from the factory
 EntityManager em = factory.createEntityManager(PersistenceContextType.EXTENDED);

 // updates take place within transactions
 EntityTransaction tx = em.getTransaction();
 tx.begin();

 // query for all employees who work in our research division
 // and put in over 40 hours a week average
 Query query = em.createQuery("select e from Employee e where "
     + "e.division.name = 'Research' AND e.avgHours &gt; 40");
 List results = query.getResultList ();

 // give all those hard-working employees a raise
 for (Object res : results) {
     Employee emp = (Employee) res;
     emp.setSalary(emp.getSalary() * 1.1);
 }

 // commit the updates and free resources
 tx.commit();
 em.close();
 factory.close();
 </programlisting>
     </example>
     <para>
 Within a container, the <classname>EntityManager</classname> will be injected
 and transactions will be handled declaratively. Thus, the in-container version
 of the example consists entirely of business logic:
     </para>
     <example id="jpa_overview_arch_interact_inside">
         <title>
             Interaction of Interfaces Inside Container
         </title>
 <programlisting>
 // query for all employees who work in our research division
 // and put in over 40 hours a week average - note that the EntityManager em
 // is injected using a @Resource annotation
 Query query = em.createQuery("select e from Employee e where "
     + "e.division.name = 'Research' and e.avgHours &gt; 40");
 List results = query.getResultList();

 // give all those hard-working employees a raise
 for (Object res : results) {
     emp = (Employee) res;
     emp.setSalary(emp.getSalary() * 1.1);
 }
 </programlisting>
     </example>
     <para>
 The remainder of this document explores the JPA interfaces in detail. We present
 them in roughly the order that you will use them as you develop your
 application.
     </para>
     <section id="jpa_overview_arch_exceptions">
         <title>
             JPA Exceptions
         </title>
         <indexterm zone="jpa_overview_arch_exceptions">
             <primary>
                 JPA
             </primary>
             <secondary>
                 exceptions
             </secondary>
             <seealso>
                 exceptions
             </seealso>
         </indexterm>
         <indexterm>
             <primary>
                 exceptions
             </primary>
             <secondary>
                 JPA
             </secondary>
         </indexterm>
         <mediaobject>
             <imageobject>
                 <!-- PNG image data, 427 x 355 (see README) -->
                 <imagedata fileref="img/jpa-exceptions.png" width="285px"/>

             </imageobject>
             <textobject>
                 <phrase>
                     JPA exception architecture
                 </phrase>
             </textobject>
         </mediaobject>
         <para>
 The diagram above depicts the JPA exception architecture. All
 exceptions are unchecked. JPA uses standard exceptions where
 appropriate, most notably <classname>IllegalArgumentException</classname>s and
 <classname>IllegalStateException</classname>s. The specification also provides
 a few JPA-specific exceptions in the <literal>javax.persistence</literal>
 package. These exceptions should be self-explanatory. See the
 <ulink url="http://java.sun.com/javaee/5/docs/api">Javadoc</ulink> for
 additional details on JPA exceptions.
         </para>
         <note>
             <para>
 All exceptions thrown by OpenJPA implement
 <ulink url="../javadoc/org/apache/openjpa/util/ExceptionInfo.html"><classname>
 org.apache.openjpa.util.ExceptionInfo</classname></ulink> to provide you with
 additional error information.
             </para>
         </note>
     </section>
 </chapter>
	<?xml version="1.0" encoding="UTF-8"?>
	<!--
	Licensed to the Apache Software Foundation (ASF) under one
	or more contributor license agreements. See the NOTICE file
	distributed with this work for additional information
	regarding copyright ownership. The ASF licenses this file
	to you under the Apache License, Version 2.0 (the
	"License"); you may not use this file except in compliance
	with the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing,
	software distributed under the License is distributed on an
	"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
	KIND, either express or implied. See the License for the
	specific language governing permissions and limitations
	under the License.
	-->
	<chapter id="jpa_overview_arch">
	<title>
	Java Persistence API Architecture
	</title>
	<indexterm zone="jpa_overview_arch">
	<primary>
	JPA
	</primary>
	<secondary>
	architecture
	</secondary>
	</indexterm>
	<para>
	The diagram below illustrates the relationships between the primary components
	of the JPA architecture.
	</para>
	<mediaobject>
	<imageobject>
	<!-- PNG image data 400 x 256 (see README) -->
	<imagedata fileref="img/jpa-arch.png" width="267px"/>

	</imageobject>
	<textobject>
	<phrase>
	JPA architecture
	</phrase>
	</textobject>
	</mediaobject>
	<note>
	<para>
	A number of the depicted interfaces are only required outside of an
	EJB3-compliant application server. In an application server, <classname>
	EntityManager</classname> instances are typically injected, rendering the
	<classname>EntityManagerFactory</classname> unnecessary. Also, transactions
	within an application server are handled using standard application server
	transaction controls. Thus, the <classname>EntityTransaction</classname> also
	goes unused.
	</para>
	</note>
	<itemizedlist>
	<listitem>
	<para>
	<indexterm>
	<primary>
	Persistence
	</primary>
	</indexterm>
	<emphasis role="bold"><link linkend="jpa_overview_persistence"><classname>
	Persistence</classname></link></emphasis>: The <classname>
	javax.persistence.Persistence</classname> class contains static helper methods
	to obtain <classname>EntityManagerFactory</classname> instances in a
	vendor-neutral fashion.
	</para>
	</listitem>
	<listitem>
	<para>
	<indexterm>
	<primary>
	EntityManagerFactory
	</primary>
	</indexterm>
	<emphasis role="bold"><link linkend="jpa_overview_emfactory"><classname>
	EntityManagerFactory</classname></link></emphasis>: The <classname>
	javax.persistence.EntityManagerFactory</classname> class is a factory for
	<classname> EntityManager</classname> s.
	</para>
	</listitem>
	<listitem>
	<para>
	<indexterm>
	<primary>
	EntityManager
	</primary>
	</indexterm>
	<emphasis role="bold"><link linkend="jpa_overview_em"><classname>EntityManager
	</classname></link></emphasis>: The <classname>javax.persistence.EntityManager
	</classname> is the primary JPA interface used by applications. Each
	<classname>EntityManager</classname> manages a set of persistent objects, and
	has APIs to insert new objects and delete existing ones. When used outside the
	container, there is a one-to-one relationship between an <classname>
	EntityManager</classname> and an <classname> EntityTransaction</classname>.
	<classname> EntityManager</classname>s also act as factories for <classname>
	Query</classname> instances.
	</para>
	</listitem>
	<listitem>
	<para>
	<indexterm>
	<primary>
	entity
	</primary>
	</indexterm>
	<emphasis role="bold"><link linkend="jpa_overview_pc"><classname>Entity
	</classname></link></emphasis>: Entites are persistent objects that represent
	datastore records.
	</para>
	</listitem>
	<listitem>
	<para>
	<indexterm>
	<primary>
	EntityTransaction
	</primary>
	</indexterm>
	<emphasis role="bold"><link linkend="jpa_overview_trans"><classname>
	EntityTransaction</classname></link></emphasis>: Each <classname>EntityManager
	</classname> has a one-to-one relation with a single <classname>
	javax.persistence.EntityTransaction</classname>. <classname>
	EntityTransaction</classname>s allow operations on persistent data to be
	grouped into units of work that either completely succeed or completely fail,
	leaving the datastore in its original state. These all-or-nothing operations
	are important for maintaining data integrity.
	</para>
	</listitem>
	<listitem>
	<para>
	<indexterm>
	<primary>
	Query
	</primary>
	</indexterm>
	<indexterm>
	<primary>
	Java Persistence Query Language
	</primary>
	<see>
	JPQL
	</see>
	</indexterm>
	<indexterm>
	<primary>
	JPQL
	</primary>
	</indexterm>
	<indexterm>
	<primary>
	JPA
	</primary>
	<secondary>
	query language
	</secondary>
	<see>
	JPQL
	</see>
	</indexterm>
	<indexterm>
	<primary>
	Structured Query Language
	</primary>
	<see>
	SQL
	</see>
	</indexterm>
	<indexterm>
	<primary>
	SQL
	</primary>
	</indexterm>
	<emphasis role="bold"><link linkend="jpa_overview_query"><classname>Query
	</classname></link></emphasis>: The <classname>javax.persistence.Query
	</classname> interface is implemented by each JPA vendor to find persistent
	objects that meet certain criteria. JPA standardizes support for queries using
	both the Java Persistence Query Language (JPQL) and the Structured Query
	Language (SQL). You obtain <classname>Query</classname> instances from an
	<classname>EntityManager</classname>.
	</para>
	</listitem>
	</itemizedlist>
	<para>
	The example below illustrates how the JPA interfaces interact to execute a JPQL
	query and update persistent objects. The example assumes execution outside a
	container.
	</para>
	<example id="jpa_overview_arch_interact_outside">
	<title>
	Interaction of Interfaces Outside Container
	</title>
	<programlisting>
	// get an EntityManagerFactory using the Persistence class; typically
	// the factory is cached for easy repeated use
	EntityManagerFactory factory = Persistence.createEntityManagerFactory(null);

	// get an EntityManager from the factory
	EntityManager em = factory.createEntityManager(PersistenceContextType.EXTENDED);

	// updates take place within transactions
	EntityTransaction tx = em.getTransaction();
	tx.begin();

	// query for all employees who work in our research division
	// and put in over 40 hours a week average
	Query query = em.createQuery("select e from Employee e where "
	+ "e.division.name = 'Research' AND e.avgHours > 40");
	List results = query.getResultList ();

	// give all those hard-working employees a raise
	for (Object res : results) {
	Employee emp = (Employee) res;
	emp.setSalary(emp.getSalary() * 1.1);
	}

	// commit the updates and free resources
	tx.commit();
	em.close();
	factory.close();
	</programlisting>
	</example>
	<para>
	Within a container, the <classname>EntityManager</classname> will be injected
	and transactions will be handled declaratively. Thus, the in-container version
	of the example consists entirely of business logic:
	</para>
	<example id="jpa_overview_arch_interact_inside">
	<title>
	Interaction of Interfaces Inside Container
	</title>
	<programlisting>
	// query for all employees who work in our research division
	// and put in over 40 hours a week average - note that the EntityManager em
	// is injected using a @Resource annotation
	Query query = em.createQuery("select e from Employee e where "
	+ "e.division.name = 'Research' and e.avgHours > 40");
	List results = query.getResultList();

	// give all those hard-working employees a raise
	for (Object res : results) {
	emp = (Employee) res;
	emp.setSalary(emp.getSalary() * 1.1);
	}
	</programlisting>
	</example>
	<para>
	The remainder of this document explores the JPA interfaces in detail. We present
	them in roughly the order that you will use them as you develop your
	application.
	</para>
	<section id="jpa_overview_arch_exceptions">
	<title>
	JPA Exceptions
	</title>
	<indexterm zone="jpa_overview_arch_exceptions">
	<primary>
	JPA
	</primary>
	<secondary>
	exceptions
	</secondary>
	<seealso>
	exceptions
	</seealso>
	</indexterm>
	<indexterm>
	<primary>
	exceptions
	</primary>
	<secondary>
	JPA
	</secondary>
	</indexterm>
	<mediaobject>
	<imageobject>
	<!-- PNG image data, 427 x 355 (see README) -->
	<imagedata fileref="img/jpa-exceptions.png" width="285px"/>

	</imageobject>
	<textobject>
	<phrase>
	JPA exception architecture
	</phrase>
	</textobject>
	</mediaobject>
	<para>
	The diagram above depicts the JPA exception architecture. All
	exceptions are unchecked. JPA uses standard exceptions where
	appropriate, most notably <classname>IllegalArgumentException</classname>s and
	<classname>IllegalStateException</classname>s. The specification also provides
	a few JPA-specific exceptions in the <literal>javax.persistence</literal>
	package. These exceptions should be self-explanatory. See the
	<ulink url="http://java.sun.com/javaee/5/docs/api">Javadoc</ulink> for
	additional details on JPA exceptions.
	</para>
	<note>
	<para>
	All exceptions thrown by OpenJPA implement
	<ulink url="../javadoc/org/apache/openjpa/util/ExceptionInfo.html"><classname>
	org.apache.openjpa.util.ExceptionInfo</classname></ulink> to provide you with
	additional error information.
	</para>
	</note>
	</section>
	</chapter>