Summary
Object-relational persistence layers offer the ability to retrieve objects from a database via an object-oriented query language. A recent IBM developerWorks tutorial by Murali Vivekanandan walks through an example of using the EJB Query Language in conjunction with Apache's Geronimo app server in constructing an online directory application.
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The EJB Query Language, or EJB-QL, was introduced in EJB 2.0, and underwent a major upgrade in the EJB 3.0 specifications. Heavily inspired by popular Java-centeric O/R mapping frameworks, such as Hibernate and Kodo, EJB-QL allows developers to express complex relational queries in an object-oriented fashion.Murali Vivekanandan's recent IBM DeveloperWorks article, Geronimo Beans and the EJB Query Language [IBM developerWorks registration required*] provides a complete example, including downloadable code, of designing and building an online directory application with EJB-QL and the open-source Apache Geronimo app server.
The tutorial offers the following sections:
Defining Entity Beans
Defining a bean class
Setting up a database
Specifying the relationships
Finders with EJB QL
Introduction to finders
Implementing a finder
Implementing a session facade
Implementing a controller layer
Building and deploying on Geronimo
Using Finders
Building a finder with parameters
Implementing finders inside business methods
Summary, Resources, and Downloadable Code
* Note: Although we pointed to this item solely because we thought our audience would find it useful, Artima is currently running a program for IBM to drive registrations at DeveloperWorks.
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