Chapter 3. Harnessing Hibernate

Size: px

Start display at page:

Download "Chapter 3. Harnessing Hibernate"

Philip Davidson
6 years ago
Views:

1 Chapter 3. Harnessing Hibernate hibernate.cfg.xml session.save() session.createquery( from Track as track ) session.getnamedquery( tracksnolongerthan ); 1 / 20

2 Configuring Hibernate using XML (hibernate.cfg.xml)... <?xml version="1.0 encoding="utf-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" " <hibernate-configuration> <session-factory>  <property name="dialect">org.hibernate.dialect.hsqldialect</property>  <property name="connection.driver_class">org.hsqldb.jdbcdriver</property> <property name="connection.url">jdbc:hsqldb:data/music</property> <property name="connection.username">sa</property> <property name="connection.password"></property> <property name="connection.shutdown">true</property> <property name= hbm2ddl.auto">update</property>... 2 / 20

3 Configuring Hibernate using XML (hibernate.cfg.xml)  <property name="connection.pool_size">1</property>  <property name="current_session_context_class">thread</property>  <property name="cache.provider_class">org.hibernate.cache.nocacheprovider</property>  <property name="jdbc.batch_size">0</property>  <property name="show_sql">true</property>  <mapping resource="com/oreilly/hh/data/track.hbm.xml"/> </session-factory> </hibernate-configuration> 3 / 20

4 Creating Persistent Objects (CreateTest.java) package com.oreilly.hh; import org.hibernate.*; import org.hibernate.cfg.configuration; import com.oreilly.hh.data.*; import java.sql.time; import java.util.date; /** * Create sample data, letting Hibernate persist it for us. */ public class CreateTest { public static void main(string args[]) throws Exception { // Create a configuration based on the XML file we've put in the standard place. Configuration config = new Configuration(); config.configure(); // Get the session factory we can use for persistence SessionFactory sessionfactory = config.buildsessionfactory(); SessionFactory sessionfactory = HibernateUtil5.getSessionFactory(); // Ask for a session using the JDBC information we've configured Session session = sessionfactory.opensession(); Transaction tx = null;... 4 / 20

5 Creating Persistent Objects (CreateTest.java) try { // Create some data and persist it tx = session.begintransaction(); Track track = new Track("Russian Trance", "vol2/album610/track02.mp3", Time.valueOf("00:03:30"), new Date(), (short)0); session.save(track); track = new Track("Video Killed the Radio Star", "vol2/album611/track12.mp3", Time.valueOf("00:03:49"), new Date(), (short)0); session.save(track); track = new Track("Gravity's Angel", "vol2/album175/track03.mp3", Time.valueOf("00:06:06"), new Date(), (short)0); session.save(track); // We're done; make our changes permanent tx.commit(); catch (Exception e) { if (tx!= null) { tx.rollback(); throw new Exception("Transaction failed", e); finally { session.close(); sessionfactory.close(); 5 / 20

6 opensession() vs getcurrentsession() With hibernate.current_session_context_class = thread Session session = sessionfactory.opensession(); Transaction tx = null; try { tx = session.begintransaction(); // do some work tx.commit(); catch (Exception e) { if (tx!= null) { tx.rollback(); throw new Exception("Transaction failed", e); finally { session.close(); Session session = sessionfactory.getcurrentsession(); Transaction tx = null; try { tx = session.begintransaction(); // do some work tx.commit(); catch (Exception e) { if (tx!= null) { tx.rollback(); throw new Exception("Transaction failed", e); opensession() always returns a new session that you have to close once you are done with the operations. getcurrentsession() returns a session bound to the current thread and that will automatically be closed when the commit or rollback. For single thread execution, if you call another getcurrentsession() then it will return you a same session object. 6 / 20

7 Gradle Tasks to Run (ch03/build.gradle) task ctest(dependson: classes, type: JavaExec) { main = 'com.oreilly.hh.createtest' classpath = sourcesets.main.runtimeclasspath task qtest(dependson: classes, type: JavaExec) { main = 'com.oreilly.hh.querytest' classpath = sourcesets.main.runtimeclasspath 7 / 20

8 Invoking the CreateTest class $ gradle ctest :ch03:compilejava UP-TO-DATE :ch03:processresources :ch03:classes :ch03:ctest Hibernate: insert into TRACK (TRACK_ID, title, filepath, playtime, added, volume) values ( default,?,?,?,?,?) Hibernate: insert into TRACK (TRACK_ID, title, filepath, playtime, added, volume) values ( default,?,?,?,?,?) Hibernate: insert into TRACK (TRACK_ID, title, filepath, playtime, added, volume) values ( default,?,?,?,?,?) BUILD SUCCESSFUL Total time: secs 8 / 20

9 Result of the CreateTest Class $ gradle db 9 / 20

10 Finding Persistent Objects (QueryTest.java) package com.oreilly.hh; import org.hibernate.*; import org.hibernate.cfg.configuration; import com.oreilly.hh.data.*; import java.sql.time; import java.util.*; public class QueryTest { public static List tracksnolongerthan(time length, Session session) { Query query = session.createquery("from Track as track " + "where track.playtime <=?"); query.setparameter(0, length, Hibernate.TIME); return query.list(); / 20

11 Finding Persistent Objects (QueryTest.java)... public static void main(string args[]) throws Exception { Configuration config = new Configuration(); config.configure(); SessionFactory sessionfactory = config.buildsessionfactory(); Session session = sessionfactory.opensession(); try { // Print the tracks that will fit in five minutes List tracks = tracksnolongerthan(time.valueof("00:05:00"), session); for ( Track atrack : tracks ) { System.out.println("Track: \"" + atrack.gettitle() + "\", " + atrack.getplaytime()); finally { session.close(); sessionfactory.close(); 11 / 20

12 Running the Query Test $ gradle qtest :ch03:compilejava UP-TO-DATE :ch03:processresources UP-TO-DATE :ch03:classes UP-TO-DATE :ch03:qtest Hibernate: select track0_.track_id as TRACK1_0_, track0_.title as title0_, track0_.filepat h as filepath0_, track0_.playtime as playtime0_, track0_.added as added0_, track0_.volume as volume0_ from TRACK track0_ where track0_.playtime<=? Track: "Russian Trance", 00:03:30 Track: "Video Killed the Radio Star", 00:03:49 BUILD SUCCESSFUL Total time: secs 12 / 20

13 Saving Objects Session.save( transient-object ) save() method saves the transient entity. Session.update( detached-object ) update() method updates the entity for persistence using the identifier of detached object. Session.saveOrUpdate( transient-object-or-detached-object ) saveorupdate() method works as save() or update() method. Session.merge( transient-object-or-detached-object ) merge() method is used to merge an object with persistent object on the basis of same identifier. The object as an argument is not changed and method returns persistent object. 13 / 20

14 Reading Objects Session.load( class, id ) It will always return a proxy (Hibernate term) without hitting the database. In Hibernate, proxy is an object with the given identifier value, its properties are not initialized yet, it just look like a temporary fake object. If no row found, it will throws an ObjectNotFoundException. Session.get(class, id ) It always hit the database and return the real object, an object that represent the database row, not proxy. If no row found, it return null. 14 / 20

15 Deleting Objects A reference to a persistent object session.delete(atrack); An HQL deletion query Query query = session.createquery("delete from Track"); query.executeupdate(); 15 / 20

16 Hibernate Object State Transient: A new instance of a persistent class which is not associated with a Session and has no representation in the database and no identifier value is considered transient by Hibernate. Persistent: You can make a transient instance persistent by associating it with a Session. A persistent instance has a representation in the database, an identifier value and is associated with a Session. Detached: Once we close the Hibernate Session, the persistent instance will become a detached instance. 16 / 20

17 Better Ways to Build Queries Query to use a named parameter: public static List tracksnolongerthan(time length, Session session) { Query query = session.createquery("from Track as track " + "where track.playtime <= :length"); query.settime("length", length); return query.list(); Track.hbm.xml : <query name="com.oreilly.hh.tracksnolongerthan"> <![CDATA[ from Track as track where track.playtime <= :length ]]> </query> Query to use a named parameter: public static List tracksnolongerthan(time length, Session session) { Query query = session.getnamedquery("com.oreilly.hh.tracksnolongerthan"); query.settime("length", length); return query.list(); 17 / 20

18 Exercise #3: Re-use Employee.java ex03/src/main/java/com/oreilly/hh/data/employee.java : package com.oreilly.hh.data; import java.util.date; public class Employee implements java.io.serializable { private Long id; private String name; public Employee() { // getters and setters 18 / 20

19 Exercise #3: Create CreateTest.java and QueryTest.java - create ex03/src/main/java/com/oreilly/hh/createtest.java * Create two employees : Lim Si Wan, Lee Sung Min - create ex03/src/main/java/com/oreilly/hh/querytest.java $ gradle ctest :ex03-final:ctest BUILD SUCCESSFUL $ gradle qtest :ex03-final:qest Employee(id: 1, name: Lim Si Wan) Employee(id: 2, name: Lee Sung Min) BUILD SUCCESSFUL 19 / 20

20 Materials for Further Study Hibernate Home Hibernate Manual Hibernate Getting Started Guide Hibernate Reference Documentation Hibernate Reference Documentation 4.3 and 5.1 Hibernate Tutorial 20 / 20

Chapter 4. Collections and Associations

Chapter 4. Collections and Associations Collections Associations 1 / 51 Java Variable and Collection class Person { Address address; class Address { Set persons = new HashSet; 2 / 51 Java