JPA Entities

CZJUG http://java.cz/jug

Java Persistence API

Martin Krajčí Systinet / HP

Content

● JPA introduction● Entities● Relationships, Inheritance, JPQL● Callbacks, Listeners, Transactions● EntityManager, PeristenceContext● Hibernate vs. Toplink, IDE support● Demo application

Java persistence comparision● September 2006 results

Primary features● Simple to use and intuitive to learn

– Configure by exception (smart defaults)● POJO development model● Object-oriented, inheritance, polymorphism, etc.● Standardized metadata for O/R mapping (annotations,

XML)● Entity detachment to other tier or JVMs● Java persistence query language ● Java SE and EE persitence model● Support pluggable persistence providers

JPA vendors● Toplink Essential (Oracle; CDDL)● Hibernate (JBoss; LGPL)● OpenJPA (Solarmetric/BEA; Apache 2.0)● Castor (Codehaus; Apache 2.0)● JPOX (JPOX; Apache 2.0)● Toplink (Oracle; commercial)● Kodo (BEA; commercial)● CocoBase (Thoughtinc; commercial)● SAP JPA (SAP; commercial)

Content

Entities● Serializable POJO annotated with

@Entity● Persistent state

– Defined by persistent fields or properties (Hibernate extension)

● @AccessType.FIELD, @AccessType.PROPERTY– Entities may also have transient state

● @Transient, transient– Optimistic locking - @Version – Can be a concrete or abstract class

Entity identification

● Persistent identity must be defined– @Id, @EmbeddedId, @IdClass

● Primary key generation - @GenerationType– TABLE, SEQUENCE, IDENTITY, AUTO

Cascade & Fetch type

● CascadeType– ALL, PERSIST, MERGE, REMOVE, REFRESH

● FetchType– LAZY, EAGER

Entity lifecycle

Update and Detach

● Updates are flushed– Before query is executed– Transaction commit– Explicit flush using EM.flush()

● Detach– Persistent context ends– EM.clear() is called– deserialized

Content

Relationships

● Supports composition and aggregation relationship– @Embedable, @ManyToOne, ...

● Relationships (uni/bi directional)– One-to-one, one-to-many, many-to-one, many-to-

many● Bidirectional relationships have

owning and inverse side● @JoinColumn for FK definition

Inheritance

● Mixed inheritance hierarchies, entities and non-entities, either concrete or abstract

● @MappedSuperclass– Doesn't map to any table, can not query

● @Inheritance– SINGLE_TABLE, JOINED, TABLE_PER_CLASS

Inheritance

JPQL● JPA supports static (named), dynamic

and native queries– @NamedQuery, precompiled, createNamedQuery()– createQuery()– @SQLResultSetMapping, createNativeQuery()

● Projection into non-existing classes● Aggregate functions, Subquery, Inner

and outer joins● Paging, Max result returned, Bind

parameter, Flush mode

Content

Callback & Listeners

● Attached to entity by @EntityListener– @PrePersist - when application calls persist()– @PostPersist – after the SQL insert– @PreRemove – when application calls remove()– @PostRemove – after the SQL delete– @PreUpdate – when a container detects that the

instance is dirty– @PostUpdate – after the SQL update– @PostLoad – after the instance was loaded

● Listener methods are defined on non-entity classes

Transactions

● In SE transactions and bootstraping must be handled by the application code– EntityTransaction

● begin(), commit(), setRollbackOnly(), rollback(), isActive()

● EE transactions are always JTA● @javax.ejb.TransactionAttribute

– REQUIRED, REQUIRES_NEW, SUPPORTS NOT_SUPPORTED, NEVER, MANDATORY

Content

Packaging

● persistence.xml● Defines

– Name of persistence unit– Transaction strategy for EM– Etities– Persistence provider– O/R mapping file (overrides annotations)

● Persistent Unit– Set of entities that are mapped to the single DB and

their mapping metadata

Entity Manager & Persistence context

● Two types of EntityManagers– Container managed in EE

● @PersistenceContext, @PersistenceUnit– Application managed in SE/EE

● EntityManager, EntityManagerFactory

● Two types of Persistence context– Transaction-scoped

● PersistenceContextType.TRANSACTION– Extended (new to java ORM)

● PersistenceContextType.EXTENDED

Content

Hibernate vs. Toplink Essential● 13 files, 4.2 MB● Cleaner DDL

generation

● 2 files, 2.5 MB● Better documentation● Checks integrity● Finer logging support● Showsql more

verbose

JPA IDE support

● Eclipse Dali plugin● Netbeans 5.5

Content

Demo application - UML

Demo application - Layers

JPA usage

● JPA + Spring using JpaDaoSupport● JPA + Spring in SE● JPA in SE● JPA in EE

● Run on Toplink Essential, Hibernate, JBoss

ReferencesNice Documentations

● http://www.oracle.com/technology/products/ias/toplink/jpa/resources-index.html● http://incubator.apache.org/openjpa/docs/openjpa-0.9.0-incubating/manual/manual.html

JPA Extensions● http://www.oracle.com/technology/products/ias/toplink/jpa/resources/toplink-jpa-extensions.html● http://www.hibernate.org/hib_docs/annotations/reference/en/html_single/#entity-hibspec

JPA IDE comparision● http://blogs.sun.com/klingo/entry/jpa_netbeans_5_5_vs

Java persistence comparision● http://www.java.net/pub/pq/122

● http://www.jpox.org/● http://jpa.hibernate.org/

Questions & Answers

● NowOR

● martin.krajci@gmail.com

Thanx for attention

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