Reviews : Java Books :
Professional EJB : The EJB 2.0 Entity Model

How Relationships are Represented

One of the most exciting aspects of the EJB 2.0 persistence specification is the comprehensive support for relationships. Relationships are between two or more entity beans that use EJB 2.0 container managed persistence. They can be unidirectional:

or bi-directional:

(can be navigated in one or both directions), and can have a multiplicity of one-to-one:

or many-to-many:

The target of a relationship must be represented by a local interface, although the source of a unidirectional relationship does not absolutely need a local interface.

Relationships are used by the EJB component developer in the following three ways:

• Accessing objects and collections of objects that are associated, based on the business logic of the application
  For instance, there might be a Collection class that represents the line items associated with a particular order. The related objects and collections of objects are retrieved by using abstract accessor methods, as described earlier. For instance, the Order object would have a getLineItems() method and a setLineItems() method that had a java.util.Set or java.util.Collection as a return value or parameter.
• Navigating between associated objects using the new EJB query language syntax
  A query can declaratively traverse the relationships of objects defined in an EJB JAR file. For instance, a query might retrieve only those orders that have a line item for the product "Spam", without knowing anything about the structure of the underlying database.
• Managing the lifespan of entity objects
  An entity object in a relationship can be cascade-deleted when its containing object is deleted.

How to Add Java Applets to Your Site

New on the Java Boutique:

New Review:

Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling API boasts simplicity, ease-of-integration, a well-rounded feature set, and it's free!

New Applet:

Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA sequences into three useful formats.

Elsewhere on internet.com:

WebDeveloper Java
Lots of Java information on webdeveloper.com

WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.

ScriptSearch Java
Hundreds of free Java code files to download.

jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.