Basic Fundamentals Conclusion

Hibernate: An Introduction

Cao Duc Nguyennguyen.cao-duc@hp.com

Software DesignerHP Software Products and Solution

May 3, 2012

Basic Fundamentals Conclusion

Talk Outline

1 BasicGetting StartedProblemChallenges

2 FundamentalsConceptsData ModelPersistent LifecycleHQLArchitecture

3 Conclusion

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Getting Started

Setting up the Environment

JDKAnt/MavenMySQL/PostgreSQL/Oracle, etc.JDBCEclipse Hibernate Tools

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Getting Started

Hibernate ORM distribution

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Problem

Hibernate - Definitions

by Hibernate.orgHibernate is concerned with helping yourapplication to achieve persistence. . . Persistencesimply means that we would like our application’sdata to outlive the applications process. . . wouldlike the state of (some of) our objects to livebeyond the scope of the JVM so that the samestate is available later.

by Wikipedia.orgHibernate is an object-relational mapping (ORM)library for the Java language, . . . a framework formapping an object-oriented domain model to atraditional relational database . . .

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Problem

Traditional View

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Problem

Traditional View (cont.)

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Problem

Hibernate View

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Challenges

Two Different Worlds

Object-Oriented SystemsSystem composed of objects interacting with each otherObjects encapsulate data and behaviors

Relational DatabasesData is stored in tables composed of rows

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Challenges

Obstacles

IdentityGranularityAssociationsNavigationInheritance & PolymorphismData type mismatches

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Concepts

Plain Old Java Object (POJOs)

In general, a POJO is a Java object not bound by any restrictionother than those forced by the Java Language Specification.However, due to technical difficulties and other reasons, in thecontext of Hibernate, a POJO is defined as follow:

No-argument class constructorProperty accessor (get/set) methodsClass is not declared final nor has final methods.Collection-typed attributes must be declared as interfacetypes.

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Data Model

Example Application: EventApp

Event-management application used to manage a conferencewith speakers, attendees, and various locations, among otherthings.

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Data Model

An Example: EventApp

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Data Model

Identity Mapping

<id name="id" column="id" type="long"><generator class="native"/></id>

Mapped classes must declare the primary key column ofthe database table.Generators using the native class will use identity orsequence columns depending on available databasesupport. If neither method is supported, the nativegenerator falls back to a high/low generator method tocreate unique primary key values.The native generator returns a short, integer, or long value.Hibernate documentation about Identity mapping here.

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Data Model

Property Mapping

<property name="startDate" column="start_date"type="date"/>

A typical Hibernate Property mapping defines a POJOproperty name, a database column name, and the name ofa Hibernate type, and it is often possible to omit the type.Hibernate uses reflection to determine the Java type of theproperty.Details about Hibernate Types mapping here.Hibernate documentation about Property mapping here.

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Data Model

Entity Mapping

<class name="Event" table="events"><!-- define identity, properties, components,collections, associations here... --></class>

A typical Hibernate Entity mapping defines a POJO classname, a database table name.By default, all class names are automatically “imported”into the namespace of HQLHibernate documentation about Entity mapping here.

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Data Model

Component Mapping

<component name="componentName"class="componentClass">

<!-- defines properties of the component herethese properties will be mapped to columns ofthe enclosing entity--></class>

A Hibernate Component mapping is defined within anEntity mapping several objects into one single table of theenclosing entity.Hibernate documentation about Component mapping here.

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Data Model

Put it all together

Hibernate Mapping files:

The Event.hbm.xml mapping file

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Data Model

Put it all together (cont.)

The Location.hbm.xml mapping file

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Data Model

Put it all together (cont.)

Hibernate Configuration hibernate.cfg.xml file:

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Data Model

Collection Mapping

Common Collections: sets, lists, bags, maps of value types.Value Type:

An object of value type has no database identity; it belongsto an entity instance, and its persistent state is embeddedin the table row of the owning entityValue-typed classes do not have identifiers or identifierproperties

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Data Model

Collection Mapping (cont.)

Hibernate persistent collections

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Data Model

Collection Mapping (cont.)

Example of persisting collections

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Data Model

Inheritance Mapping

Table per concrete class with union:

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Data Model

Inheritance Mapping (cont.)

Table per class hierarchy:

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Data Model

Inheritance Mapping (cont.)

Table per subclass:

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Persistent Lifecycle

Object States

TransientThe object is not associated with any persistencecontext. It has no persistent identity (primary keyvalue).

PersistentThe object is currently associated with apersistence context. It has a persistent identity(primary key value) and, perhaps, a correspondingrow in the database. Hibernate guarantees thatpersistent identity is equivalent to Java identity.

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Persistent Lifecycle

Object States (cont.)

DetachedThe instance was once associated with apersistence context, but that context was closed,or the instance was serialized to another process.It has a persistent identity and, perhaps, acorrsponding row in the database. For detachedinstances, Hibernate makes no guarantees aboutthe relationship between persistent identity andJava identity

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Persistent Lifecycle

State Transition Diagram

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Persistent Lifecycle

Case 1: Making an object persistent

Item item = new Item();item.setName("Playstation3 incl. all accessories");item.setEndDate( ... );Session session = sessionFactory.openSession();Transaction tx = session.beginTransaction();Serializable itemId = session.save(item);tx.commit();session.close();

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Persistent Lifecycle

Case 2: Retrieving a persistent object

Session session = sessionFactory.openSession();Transaction tx = session.beginTransaction();Item item = (Item) session.load(Item.class,new Long(1234));// Item item = (Item) session.get(Item.class,// new Long(1234));tx.commit();session.close();

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Persistent Lifecycle

Case 3: Modifying a persistent object

Session session = sessionFactory.openSession();Transaction tx = session.beginTransaction();Item item = (Item) session.get(Item.class,new Long(1234));item.setDescription("This Playstation isas good as new!");tx.commit();session.close();

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Persistent Lifecycle

Case 4: Making a persistent object transient

Session session = sessionFactory.openSession();Transaction tx = session.beginTransaction();Item item = (Item) session.load(Item.class,new Long(1234));session.delete(item);tx.commit();session.close();

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Persistent Lifecycle

Case 5: Reattaching a modified detached instance

// Loaded in previous Sessionitem.setDescription(...);Session sessionTwo = sessionFactory.openSession();Transaction tx = sessionTwo.beginTransaction();sessionTwo.update(item);item.setEndDate(...);tx.commit();sessionTwo.close();

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HQL

Query

HQL Query:

HQL SQLQuery:

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HQL

Parameter Binding

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HQL

Joins

Join:

Left Join:

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HQL

Criteria API

Some developers prefer to build queries dynamically, using anobject-oriented API, rather than building query strings.Hibernate provides an intuitive org.hibernate.Criteriarepresents a query against a particular persistent class:

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HQL

DetachedCriteria

A DetachedCriteria is used to express a subquery.

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Architecture

Structural Components

More in depth explanation can be found here.

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Architecture

Hibernate Flexibility and Extendibility

Extension points:Dialects (for different databases)Custom mapping typesID generatorsCache, CacheProviderTransaction, TransactionFactoryPropertyAccessorProxyFactoryConnectionProvider

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Why Hibernate?

Free, open source Java packageRelease developers from data persistent related tasks,help to focus on objects and features of applicationNo need for JDBC API for Result handlingDatabase almost-independenceEfficient queries

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THANK YOU *-*