JPA - Java Persistence API

1. JPA - Java Persistence API Thomas Wöhlke ObjectCode GmbH 12.03.2009

4. Object-Relational Mapping <ul><li>Analogie: OO  RDB </li></ul><ul><li>Klasse  Tabelle </li></ul><ul><li>Objekt  Zeile </li></ul><ul><li>Variable  Spalte </li></ul><ul><li>Wert  Feld </li></ul><ul><li>Domain Object Modell = ERD ? </li></ul>© 2009 ObjectCode GmbH

8. ... und die Physik? <ul><li>v(Harddisk) << v(RAM) </li></ul><ul><li>CPU 99% idle </li></ul><ul><li>Process 99% IO_WAIT </li></ul><ul><li>Page Impressions  SQL-Requests? </li></ul>© 2009 ObjectCode GmbH

10. Hibernate <ul><li>Mapping von POJO‘s: </li></ul><ul><li>Java Bean API </li></ul><ul><li>Collection API (Generics) </li></ul><ul><li>Mapping: XML oder Hibernate-Annotations </li></ul><ul><li>Hibernate ist ein JPA-Vendor: </li></ul><ul><li>Hibernate-Core </li></ul><ul><li>Hibernate-Annotations </li></ul><ul><li>Hibernate Entity Manager </li></ul>© 2009 ObjectCode GmbH

13. persistence.xml (Java EE) <ul><li><?xml version="1.0" encoding="UTF-8"?> </li></ul><ul><li><persistence xmlns="http://java.sun.com/xml/ns/persistence" </li></ul><ul><li>xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" </li></ul><ul><li>xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" </li></ul><ul><li>version="1.0"> </li></ul><ul><li><persistence-unit name="JPM_DB"> </li></ul><ul><li><provider>org.hibernate.ejb.HibernatePersistence</provider> </li></ul><ul><li><jta-data-source>java:/JpmDS</jta-data-source> </li></ul><ul><li><properties> </li></ul><ul><li><property name="hibernate.hbm2ddl.auto" value="create-drop"/> </li></ul><ul><li><property name="hibernate.show_sql" value="true"/> </li></ul><ul><li> </li></ul><ul><li><property name="hibernate.cache.provider_class" value="org.hibernate.cache.HashtableCacheProvider"/> </li></ul><ul><li><property name="hibernate.transaction.manager_lookup_class" </li></ul><ul><li>value="org.hibernate.transaction.JBossTransactionManagerLookup"/> </li></ul><ul><li></properties> </li></ul><ul><li></persistence-unit> </li></ul><ul><li></persistence> </li></ul>© 2009 ObjectCode GmbH

14. persistence.xml (Java SE) <ul><li><?xml version="1.0" encoding="UTF-8"?> </li></ul><ul><li><persistence xmlns="http://java.sun.com/xml/ns/persistence" </li></ul><ul><li>xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" </li></ul><ul><li>xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" </li></ul><ul><li>version="1.0"> </li></ul><ul><li><persistence-unit name="JPM_DB"> </li></ul><ul><li><provider>org.hibernate.ejb.HibernatePersistence</provider> <class>org.woehlke.projecteering.kernel.calendar.pao.Day</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.minutes.pao.Event</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.minutes.pao.Minutes</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.minutes.pao.MinutesItem</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.projects.pao.Project</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.projects.pao.ProjectCategory</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.timerecording.pao.TimeRecordingItem</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.userrights.pao.Company</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.userrights.pao.Team</class> </li></ul><ul><li><class>org.woehlke.projecteering.kernel.userrights.pao.User</class> </li></ul><ul><li><exclude-unlisted-classes>true</exclude-unlisted-classes> </li></ul><ul><li><properties> </li></ul><ul><li><property name="hibernate.hbm2ddl.auto" value="create-drop"/> </li></ul><ul><li><property name="hibernate.show_sql" value="true"/> </li></ul><ul><li><property name="hibernate.generate_statistics" value="true"/> </li></ul><ul><li><property name="hibernate.show_sql" value="true"/> </li></ul><ul><ul><li><property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/> </li></ul></ul><ul><li><property name="hibernate.connection.username" value="jpm"/> </li></ul><ul><li><property name="hibernate.connection.password" value="jpmpwd"/> </li></ul><ul><li><property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/jpm"/> </li></ul><ul><li><property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/> </li></ul><ul><li></properties> </li></ul><ul><li></persistence-unit> </li></ul><ul><li></persistence> </li></ul>© 2009 ObjectCode GmbH

15. Mapping der Klassen 1 <ul><li>public class Customer extends Person { </li></ul><ul><li>@OneToMany(mappedBy=“purchaser”) Set<Order> orders = </li></ul><ul><li>new HashSet<Order>(); </li></ul><ul><li>protected Customer() { } // for loading from db </li></ul><ul><li>public Customer(String fname, String lname) { </li></ul><ul><li>super(fname, lname); </li></ul><ul><li>} </li></ul><ul><li>public void addOrder(Order o) { orders.add(o); } </li></ul><ul><li>public Set<Order> getOrders() { return orders; } </li></ul><ul><li>} </li></ul>© 2009 ObjectCode GmbH

16. Mapping der Klassen 2 <ul><li>@Entity </li></ul><ul><li>@Table(name=“PRODUCTS”) </li></ul><ul><li>public class Product { </li></ul><ul><li>@Id @GeneratedValue </li></ul><ul><li>@Column(name=“PRODUCT_PK”) </li></ul><ul><li>long id; </li></ul><ul><li>@Version int oplock; // column defaults to “OPLOCK” </li></ul><ul><li>String name; // column defaults to “NAME” </li></ul><ul><li>@ManyToOne </li></ul><ul><li>@JoinColumn(name=“SUPP_FK”, referencedColumnName=“SUPP_PK”) </li></ul><ul><li>Supplier supplier; </li></ul><ul><li>... </li></ul><ul><li>} </li></ul>© 2009 ObjectCode GmbH

17. Mapping der Assoziationen <ul><li>Kardinalität: </li></ul><ul><li>1:1  OneToOne </li></ul><ul><li>1:n  OneToMany </li></ul><ul><li>n:m  ManyToMany </li></ul><ul><li>Richtung: </li></ul><ul><li>1:n -> OneToMany </li></ul><ul><li>N:1 <- ManyToOne </li></ul><ul><li>Sichtbarkeit: </li></ul><ul><li>Unidirektional -> </li></ul><ul><li>Bidirektional <-> </li></ul>© 2009 ObjectCode GmbH

18. Mapping der Vererbung <ul><li>Eine Tabelle pro Klassen-Hierarchie </li></ul><ul><li>Eine Tabelle pro konkrete Klasse </li></ul><ul><li>Eine Tabelle pro Subklasse </li></ul><ul><li>Non-Entity Vererbung </li></ul><ul><li>Keine Vererbung: Embbeding </li></ul>© 2009 ObjectCode GmbH

20. Einsatz von JPA im JBoss/EJB3 <ul><li>@Stateless </li></ul><ul><li>public class MinutesItemDao extends BaseDao<MinutesItem> implements IMinutesItemDao { </li></ul><ul><li>@PersistenceContext(unitName = "JPM_DB" ) </li></ul><ul><li>private EntityManager entityManager; </li></ul><ul><li>public MinutesItem findById(Long id) { </li></ul><ul><li>return entityManager.find(MinutesItem.class,id); </li></ul><ul><li>} </li></ul><ul><li>public EntityManager getEntityManager() { </li></ul><ul><li>return entityManager; </li></ul><ul><li>} </li></ul><ul><li>public void setEntityManager(EntityManager entityManager) { </li></ul><ul><li>this.entityManager = entityManager; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>© 2009 ObjectCode GmbH

21. Einsatz von JPA in Spring/Tomcat <ul><li>@Transactional </li></ul><ul><li>public class MinutesDao extends BaseDao<Minutes> implements IMinutesDao { </li></ul><ul><li>public Minutes findById(Long id) { </li></ul><ul><li>return jpaTemplate.find(Minutes.class,id); </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>© 2009 ObjectCode GmbH

22. EJB-QL <ul><li>Query q = em.createQuery(“select c from Customer c where c.firstName = :fname order by c.lastName”); </li></ul><ul><li>q.setParameter(“fname”, “Joe”); </li></ul><ul><li>q.setFirstResult(20); </li></ul><ul><li>q.setMaxResults(10); </li></ul><ul><li>List<Customer> customers = (List<Customer>) q.getResultList() ; </li></ul><ul><li>// all orders, as a named query </li></ul><ul><li>@Entity </li></ul><ul><li>@NamedQuery(name=“Order:findAllOrders”, </li></ul><ul><li>query=“select o from Order o”); </li></ul><ul><li>public class Order { ... } </li></ul><ul><li>Query q = em.createNamedQuery(“Order:findAllOrders”); </li></ul>© 2009 ObjectCode GmbH

23. Lebenszyklus Persistente Objekte <ul><li>Neu, transient (@Id id == null) </li></ul><ul><li>Persistent (@Id id != null) </li></ul><ul><li>Detached: </li></ul><ul><ul><li>Wie persistent (@Id id!= null) </li></ul></ul><ul><ul><li>Jedoch ausserhalb des EntityManager Kontext </li></ul></ul><ul><ul><li>Lazy Loading nicht möglich! </li></ul></ul><ul><ul><li>Änderungen in DB sichern mit merge </li></ul></ul>© 2009 ObjectCode GmbH

24. EJB-QL <ul><li>// all people, via a custom SQL statement </li></ul><ul><li>Query q = em.createNativeQuery(“SELECT ID, VERSION, SUBCLASS, FIRSTNAME, LASTNAME FROM PERSON”, Person.class); </li></ul><ul><li>List<Person> people = (List<Person>) q.getResultList() ; </li></ul><ul><li>// single-result aggregate: average order total price </li></ul><ul><li>Query q = em.createQuery( “select avg(i.price) from Item i” ); </li></ul><ul><li>Number avgPrice = (Number) q.getSingleResult(); </li></ul><ul><li>// traverse to-many relations </li></ul><ul><li>Query q = em.createQuery( “ select o from Order o left join o.items li where li.price > :price ”); </li></ul><ul><li>q.setParameter(“price”, 1000); </li></ul><ul><li>List<Order> orders = (List<Order>) q.getResultList(); </li></ul>© 2009 ObjectCode GmbH

25. Lazy Loading <ul><li>Supplier s = order.getItem().getProduct().getSupplier(); </li></ul><ul><li>Bei Aufruf eines Getters wird Objekt aus DB-Zeile nachgeladen. </li></ul><ul><li>Ohne Lazy Loading muss komplettes Objekt-Netz geladen werden. </li></ul><ul><li>Struktur des Objekt-Netzes variiert je nach Web-View </li></ul>© 2009 ObjectCode GmbH

27. Ausblick: Seam <ul><li>Kern-Entwickler von Hibernate sind nun im Seam-Projekt </li></ul><ul><li>O/R-Mapping von EJB3/JPA auch für die Webapplikation </li></ul><ul><li>OO im Datenbankbackend durch ORM </li></ul><ul><li>OO im Webfrontend durch JSF </li></ul><ul><li>Im Conversation-Scope ist Lazy-Loading möglich. </li></ul><ul><li>Detached Objects können für die Webview verwendet werden: Kein DTO-Antipattern </li></ul>© 2009 ObjectCode GmbH

28. <ul><li>RTFM: http://www.hibernate.org/ </li></ul><ul><li>O‘Reilly: Enterprise JavaBeans 3.0 </li></ul><ul><li>Manning: EJB3 in Action </li></ul><ul><li>Manning: Hibernate in Action </li></ul>Literatur © 2009 ObjectCode GmbH