Hibernate

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Hibernate
An object-relational mapping tool for Java
by Dan Kigelman
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Scenario

• Too many books, too few readers
• Want to share with friends (mock-library)
• Need to keep track of
• title
• author
• description
• available?
• current location

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It starts with an object
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Direct Java JDBC Approach

• Imagine
• more classes
• more methods

Cons

• Tedious
• Repetative
• Error-prone
• DB-specific

Pros

• Very flexible
• Direct access to SQL

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Object-relational mapping (ORM)

• Maps java objects to database
• tendency towards enlightened lazinesshttp//www
  .onjava.com/pub/a/onjava/2005/09/21/what-is-hibern
  ate.html
• Saves time and sanity
• Usually at the loss of flexibility
• (ORM controversy)
• Many ORM tools exist

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Hibernate features

• Unobtrusive few changes to java classes
• We keep our Plain Old Java Objects
• Class must have no-parameter constructor
• Class must follow java naming convention for
  attributes, getters, and setters
• Open-source (LGPL)
• Vendor-independent
• Oracle, DB2, Sybase, MS SQL Server, PostgreSQL,
  MySQL, HypersonicSQL, Mckoi SQL, SAP DB,
  Interbase, Pointbase, Progress, FrontBase,
  Ingres, Informix, Firebird
• Flexible supports object association,
  inheritance, and polymorphism

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Book.hbm.xml

• This tells Hibernate which classes to make
  persistent
• Mapping java class to db fields
• Hibernate uses get/set methods for each property
• Highly customizable

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Hibernate.cfg.xml

• Select DB Dialect(currently hsql)
• Creates / updates schema if needed

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Simple Queries
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Relations objects as attributes

• Supports one-to-many, many-to-many relationships
• Classes behave naturally
• Changes made to
• Book.hbm.xml
• Friend.hbm.xml

public class Friend private String
name private String address private Book
books ... public class Book private Long
id private String title ... private Friend
currentReader ...
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Advanced Queries

• Supports both HQL (Hibernate Query Language) and
  SQL
• Exampleselect count(payment), status.name from
  Payment as payment join payment.currentStatus
  as status join payment.statusChanges as
  statusChangewhere payment.status.name ltgt
  PaymentStatus.AWAITING_APPROVAL or (
  statusChange.timeStamp ( select
  max(change.timeStamp) from
  PaymentStatusChange change where
  change.payment payment ) and
  statusChange.user ltgt currentUser )group by
  status.name, status.sortOrderorder by
  status.sortOrder

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Resources and References

• Hibernate.org
• Getting started quicklyhttp//www.hibernate.org/
  152.html
• Tutorialhttp//www.hibernate.org/hib_docs/v3/refe
  rence/en/html/tutorial.html
• Eloquent overview http//www.onjava.com/pub/a/onj
  ava/2005/09/21/what-is-hibernate.html
• Another tutorialhttp//www.onjava.com/pub/a/onja
  va/2004/01/14/hibernate.html
• Wikipedia
• http//en.wikipedia.org/wiki/Object-relational_map
  pingObject-Relational_mapping_utilities
• http//en.wikipedia.org/wiki/Hibernate_28Java29
• HypersonicSQL - 100 Java Database (open-source)
• http//www.hsqldb.org