Blue Elephant Referee Scheduler

Using Hibernate

Intro:

This project uses a tool called Hibernate, which is an object-relationl mapping tool.  This tool allows us to write a model layer, which encapsulates the business logic of the application, using Java objects.  Hibernate transparently maps these objects into tables in a (MySQL) database.  The mappings are xml files, one per Java class.

Motivation:

Hibernate abstacts a large amount of the grunt work associated with persistence.  There is no hand-written JDBC code in our application. Hand-writing JDBC code is tedious, error-prone, and time-consuming. Hibernate also provides built-in implementations of other useful design patterns, such as lazy-load, and optimistic locking for concurrency control. Hibernate also provides a layer of abstraction which hides underlying transactional strategies, which in our case is JDBC database transactions.  We explain this more thoroughly in the short paper on concurrency and transactions.

Usage:

Our model layer components are located in the model package.  This package also contains the mapping files for these objects, which have corresponding filenames, with a .hbm suffix.  For example, the Referee type, which is implemented with the class Referee.java, is mapped in the file Referee.hbm.xml. 

We take advantage of the following Hibernate features:

• Automatic Primary Key Generation – Hibernate generates unique, meaningless primary keys that are optimized for the MySQL database.  Use of this feature requires each model object to have an ‘id’ field, which we include in a base class called ModelType.
• Optimistic Locking for concurrency – Hibernate manages a per object version number.  Attempted updates or deletes to database records must use the current version number to succeed. This feature requires each model object to have a ‘version’ field, which we again include in the base class ModelType.
• Mapping a class hierarchy into a single datavase table:  Hibernate maps the classes Referee and Administrator to the same table – user, and transparently manages keeping track of type. 

Links:

Getting started with Hibernate is pretty painless.  The online documentation is quite good, and a comprehensive book, Hibernate in Action, should be published by August 2004.  Also check out the following articles and tutorials listed on the Hibernate website.