Apple WebObjects 3.5 Tools And Techniques - Manual (Page 63)

Chapter 3 Working With Dynamic Elements
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Note: To delete a key or action, you must delete it from the source code in Project
Builder. Also, the Add Variable/Method and Add Action commands apply only
to a component’s code file. To add variables and methods to the application and
session code files, or to any other code files, you must edit them directly in
Project Builder.
Adding Display Groups
A display group is an important type of variable that you use in WebObjects
applications that access databases. A display group is an object that can fetch,
insert, delete, display, update and search records in a database.
This section describes the mechanics of adding display groups to a WebObjects
project. For detailed information about display groups, see the DisplayGroup
(Java) or WODisplayGroup (Objective-C) class specification in the WebObjects
Class Reference. To learn more about how to create a WebObjects database
application, see “Creating a WebObjects Database Application” in Getting
Started With WebObjects.
WebObjects applications access databases through the Enterprise Objects
Framework, which represents database rows as enterprise objects. Enterprise
object classes typically correspond to database tables, and an enterprise object
instance corresponds to a single row or record in a table. For detailed
information on enterprise objects, read the Enterprise Objects Framework
Developer’s Guide.
In a database application, you use entity-relationship models. A model associates
database columns with instance variables of objects. You create a model with the
EOModeler application, or you can specify one when you use the Wizard to set
up your application (when you add a model to your project, it is added to the
Resources suitcase). A model is stored in a model file. For more information on
creating models, see the chapter “Using EOModeler” in Enterprise Objects
Framework Developer’s Guide.
A model contains entities, attributes, and relationships. An entity associates a
database table with an enterprise object class. Display groups manage objects
associated with a single entity. An attribute associates a database column with an
instance variable. A relationship is a link between two entities that’s based on
attributes of the entities.
If you used the Wizard to set up your application, a display group was set up for
you based on the model you specified. There are several other ways to create a
display group: