Introduction to WebObjects Enterprise Objects Programming Guide

An overview of the technology that combines object-oriented programming with database application development. Includes examples and solutions.

Who Should Read This Document

This document is appropriate for Enterprise Objects developers of all levels, but much of the material is more relevant to intermediate and advanced users who are working with fairly complex applications. However, the appendix Principal Methods and many of the tasks sections throughout the document provide introductory information to help new users get started with the Enterprise Objects frameworks.

New Enterprise Objects developers should consider the document EOModeler User Guide a prerequisite to this document. As well as teaching you how to use EOModeler, it is the best way to familiarize yourself with general database concepts and with the core concepts in the Enterprise Objects frameworks such as data modeling. It also discusses the most important characteristics of EOEnterpriseObjects, rather than discussing the mechanics of the Enterprise Objects frameworks, as this book does.

Road Map to Concepts and Road Map to Tasks provide road maps to help you decide which sections of this document are most relevant to you.

Terminology

This section provides a key to some of the overloaded terms in the Enterprise Objects frameworks:

the Enterprise Object technology is also referred to as “Enterprise Objects” (note capitalization) or as the “Enterprise Objects frameworks”

classes or instances of classes that implement the EOEnterpriseObject interface are referred to as “enterprise objects” (note capitalization)

The terms “Enterprise Objects,” “the Enterprise Objects frameworks,” and “the Enterprise Object technology” refer to all of the classes in WebObjects that begin with the prefix “EO.” This document speaks specifically to the core Enterprise Objects frameworks: classes in the package com.webobjects.eocontrol (referred to as the control layer ) and classes in the package com.webobjects.eoaccess (referred to as the access layer ).

How to Learn About Enterprise Objects

The Enterprise Objects frameworks provide a great deal of flexibility through an extensive API—most of which you’ll never need to use or know about. You can go far in building an Enterprise Objects application if you’re familiar with a handful of classes and a few dozen methods. The best way to learn about these particular classes and methods is by performing small, focused tasks to gradually get acquainted with the commonly used ones. By learning the technology through these tasks, you build up a set of mental tools that you can later use to build real, data-driven applications. This document provides a number of these tasks to help you get started.

While learning the technology, don’t be tempted to use classes and methods that you either don’t need or don’t understand. You’ll probably ever use only 10% of the public API throughout the technology, so don’t be too adventurous in the beginning. An axiom of Enterprise Objects development is that “he who writes the least code wins.” That is, if in dealing with a particular problem, you end up writing a lot of complicated, custom code, you’ve probably overlooked functionality that the frameworks provide.

When learning this technology, keep in mind that the learning curve is high but the productivity that results allows you to rapidly build sophisticated, elegant business solutions in a fraction of the time that other database application development systems require. To help tackle the high learning curve, don’t try to understand the whole system at once. Fortunately, the layered design of Enterprise Objects facilitates this approach. By working with one layer at a time, the whole system gradually comes into focus.

Part of the difficultly in learning Enterprise Objects is its abstract architecture. It is designed to allow you to work with data sources at an abstract level; it allows you to work with objects that are abstractions of data sources. The objects within the frameworks provide abstract representations of databases, of database transactions, and of the data retrieved from databases.

Although the abstractions within Enterprise Objects contribute to its high learning curve, once you understand the architecture, you’ll see that its abstract design provides huge benefits in terms of portability to different data sources and to various client-server application configurations. So if all the abstraction at first seems confusing, be patient—you’ll eventually come to appreciate it.

Road Map to Concepts

If you’ve read Using EOModeler or have a little experience building Enterprise Objects applications, you should read these chapters first:

Enterprise Objects Overview

Business Objects

Business Logic

If you are an intermediate developer who wants to know more about the mechanics of Enterprise Objects, read these chapters:

Fetching Data

Working With the Object Graph

Saving Data

If you are an advanced developer, you may be interested in these chapters, which discuss advanced topics:

Core Framework Stack

Update Strategies

Connecting to a Database

Concurrency

Road Map to Tasks

If you’ve read Using EOModeler or have a little experience building Enterprise Objects applications, you are probably interested in the tasks described in these sections:

Synchronizing Model Changes to Class Files

Instantiating Enterprise Objects

Providing Initial Values

Adding Validation

Writing Business Methods

Manipulating Relationships

Building a Reusable Framework

Constructing Fetch Specifications

Filtering Fetch Results in Memory

Sorting Fetch Results in Memory

Accessing WebObjects in Enterprise Objects

Intermediate and advanced developers are probably interested in the tasks in these sections:

Providing Separate Stacks

Accessing Lower-Level Objects

Generating Custom Primary Keys

Using Compound Primary Keys

Recovering and Refaulting

Recovering and Last Write Wins

Providing a Connection Dictionary in Code

Providing Multiple Database Channels

Closing Database Channels

Accessing Database Keys