Apple WebObjects 3.5 - Manual (Page 80)

Chapter 3 Creating a WebObjects Database Application
80
Examining the Variables
1. Double-click Main.wo in Project Builder’s WebObjects Components category
to open the Main component in WebObjects Builder.
There are four variables in the object browser: the application and session
variables that are available in all components and two others, movie and
movieDisplayGroup .
The movie variable is an enterprise object that represents a row fetched from
the MOVIE table. movieDisplayGroup is a display group—an object that interacts
with a database, indirectly through classes in the Enterprise Objects
Framework. Display groups are used to fetch, insert, update, and delete
enterprise objects that are associated with a single entity.
movieDisplayGroup ’s
entity is Movie, which you specified in the wizard’s “Choose an entity”
page.
2. In Project Builder, look at the class file Main.java to see how movie is declared.
The movie declaration (shown below) declares movie to be an
EnterpriseObject—a Java interface that describes the general behavior that
all enterprise objects must have.
/** @TypeInfo Movie */ protected EnterpriseObject movie;
At run time, movie is a GenericRecord object. Recall that GenericRecord
is used to represent enterprise objects unless you specify a custom class.
Since you didn’t check the “Use custom enterprise objects” box in the
wizard’s “Choose what to include in your model” page, your application
defaults to using GenericRecord for all its entities.
The comment ( /** @TypeInfo Movie */ ) is used by WebObjects
Builder to identify movie ’s entity (Movie). Knowing the entity allows
WebObjects Builder to display movie ’s attributes ( category , dateReleased , and
so on). You can see movie ’s attributes if you select the movie variable in the
WebObjects Builder’s object browser.
3. In Project Builder, examine movieDisplayGroup ’s declaration in Main.java .
The declaration (shown below) declares movieDisplayGroup to be a
DisplayGroup.
protected DisplayGroup movieDisplayGroup;