Apple WebObjects 3.5 Manual de usuario descargar pdf (Pagina 80)

Chapter 3 Creating a WebObjects Database Application

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;

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Apple WebObjects 3.5 Manual de usuario Pagina 80

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