JPA - Java Persistence API

JPA - Java Persistence API Thomas Wöhlke ObjectCode GmbH 12.03.2009

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

persistence.xml (Java EE) <?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="JPM_DB"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <jta-data-source>java:/JpmDS</jta-data-source> <properties> <property name="hibernate.hbm2ddl.auto" value="create-drop"/> <property name="hibernate.show_sql" value="true"/>  <property name="hibernate.cache.provider_class" value="org.hibernate.cache.HashtableCacheProvider"/> <property name="hibernate.transaction.manager_lookup_class" value="org.hibernate.transaction.JBossTransactionManagerLookup"/> </properties> </persistence-unit> </persistence> © 2009 ObjectCode GmbH

persistence.xml (Java SE) <?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="JPM_DB"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <class>org.woehlke.projecteering.kernel.calendar.pao.Day</class> <class>org.woehlke.projecteering.kernel.minutes.pao.Event</class> <class>org.woehlke.projecteering.kernel.minutes.pao.Minutes</class> <class>org.woehlke.projecteering.kernel.minutes.pao.MinutesItem</class> <class>org.woehlke.projecteering.kernel.projects.pao.Project</class> <class>org.woehlke.projecteering.kernel.projects.pao.ProjectCategory</class> <class>org.woehlke.projecteering.kernel.timerecording.pao.TimeRecordingItem</class> <class>org.woehlke.projecteering.kernel.userrights.pao.Company</class> <class>org.woehlke.projecteering.kernel.userrights.pao.Team</class> <class>org.woehlke.projecteering.kernel.userrights.pao.User</class> <exclude-unlisted-classes>true</exclude-unlisted-classes> <properties> <property name="hibernate.hbm2ddl.auto" value="create-drop"/> <property name="hibernate.show_sql" value="true"/> <property name="hibernate.generate_statistics" value="true"/> <property name="hibernate.show_sql" value="true"/> <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/> <property name="hibernate.connection.username" value="jpm"/> <property name="hibernate.connection.password" value="jpmpwd"/> <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/jpm"/> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/> </properties> </persistence-unit> </persistence> © 2009 ObjectCode GmbH

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

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

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

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

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

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

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

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

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

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

JPA - Java Persistence API

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