php objects patterns and practice

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PHP Objects,
Patterns, and
Practice
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object-oriented enhancements, design patterns,
and essential development tools

THIRD EDITION
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Matt Zandstra

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PHP Objects, Patterns,
and Practice
Third Edition

■■■
Matt Zandstra

i

PHP Objects, Patterns, and Practice, Third Edition
Copyright © 2010 by Matt Zandstra
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ii

Contents at a Glance

■Contents at a Glance.......................................................................................................................iii

■Contents .......................................................................................................................................... v

■About the Author ......................................................................................................................... xvii

■About the Technical Reviewer .................................................................................................... xviii

■Acknowledgments ........................................................................................................................ xix

■Introduction to the Third Edition ................................................................................................... xx
Part 1: Introduction.............................................................................................................................1

■Chapter 1: PHP: Design and Management .......................................................................................3
Part 2: Objects ....................................................................................................................................9
■Chapter 2: PHP and Objects...........................................................................................................11
■Chapter 3: Object Basics ...............................................................................................................15
■Chapter 4: Advanced Features.......................................................................................................41
■Chapter 5: Object Tools..................................................................................................................71
■Chapter 6: Objects and Design ......................................................................................................99
Part 3: Patterns...............................................................................................................................121
■Chapter 7: What Are Design Patterns? Why Use Them? ..............................................................123
■Chapter 8: Some Pattern Principles ............................................................................................131
■Chapter 9: Generating Objects.....................................................................................................145
■Chapter 10: Patterns for Flexible Object Programming...............................................................169
■Chapter 11: Performing and Representing Tasks........................................................................189
■Chapter 12: Enterprise Patterns ..................................................................................................221
■Chapter 13: Database Patterns....................................................................................................275
Part 4: Practice...............................................................................................................................315
■Chapter 14: Good (and Bad) Practice ..........................................................................................317
■Chapter 15: An Introduction to PEAR and Pyrus..........................................................................323
■Chapter 16: Generating Documentation with phpDocumentor ....................................................347
■Chapter 17: Version Control with Subversion..............................................................................361

■Chapter 18: Testing with PHPUnit................................................................................................379
■Chapter 19: Automated Build with Phing ....................................................................................407
■Chapter 20: Continuous Integration.............................................................................................427
Part 5: Conclusion...........................................................................................................................451
■Chapter 21: Objects, Patterns, Practice ......................................................................................453
■Appendix A: Bibliography ............................................................................................................463
■Appendix B: A Simple Parser.......................................................................................................467
■Index............................................................................................................................................219

iii

iv

Contents

■Contents at a Glance ............................................................................................iii

■Contents ................................................................................................................v

■About the Author ............................................................................................... xvii

■About the Technical Reviewer.......................................................................... xviii

■Acknowledgments.............................................................................................. xix

■Introduction to the Third Edition ......................................................................... xx
Part 1: Introduction ..................................................................................................1
■Chapter 1: PHP: Design and Management.............................................................3
The Problem.................................................................................................................... 3
PHP and Other Languages .............................................................................................. 4
About This Book .............................................................................................................. 5
Objects ...................................................................................................................................................6
Patterns..................................................................................................................................................6
Practice ..................................................................................................................................................6
What’s New in the Third Edition.............................................................................................................7

Summary......................................................................................................................... 7
Part 2: Objects..........................................................................................................9
■Chapter 2: PHP and Objects ................................................................................11
The Accidental Success of PHP Objects ....................................................................... 11
In the Beginning: PHP/FI ......................................................................................................................11
Syntactic Sugar: PHP 3 ........................................................................................................................11
PHP 4 and the Quiet Revolution ...........................................................................................................12


v

■ CONTENTS

Change Embraced: PHP 5 ....................................................................................................................13

Into the Future .............................................................................................................. 14
Advocacy and Agnosticism: The Object Debate............................................................ 14
Summary....................................................................................................................... 14
■Chapter 3: Object Basics .....................................................................................15
Classes and Objects...................................................................................................... 15
A First Class .........................................................................................................................................15
A First Object (or Two) .........................................................................................................................16

Setting Properties in a Class........................................................................................ 17
Working with Methods .................................................................................................. 19
Creating a Constructor Method ............................................................................................................21

Arguments and Types ................................................................................................... 22
Primitive Types ....................................................................................................................................22
Taking the Hint: Object Types ..............................................................................................................25

Inheritance .................................................................................................................... 27
The Inheritance Problem......................................................................................................................27
Working with Inheritance.....................................................................................................................31
Public, Private, and Protected: Managing Access to Your Classes ......................................................35

Summary....................................................................................................................... 39
■Chapter 4: Advanced Features ............................................................................41
Static Methods and Properties...................................................................................... 41
Constant Properties ...................................................................................................... 44
Abstract Classes ........................................................................................................... 45
Interfaces ...................................................................................................................... 47
Late Static Bindings: The static Keyword.................................................................. 48
Handling Errors ............................................................................................................. 51
Exceptions............................................................................................................................................52

Final Classes and Methods ........................................................................................... 57
Working with Interceptors ............................................................................................ 58
Defining Destructor Methods ........................................................................................ 62

vi

■ CONTENTS

Copying Objects with __clone() .................................................................................... 63
Defining String Values for Your Objects........................................................................ 65
Callbacks, Anonymous Functions and Closures ........................................................... 66
Summary....................................................................................................................... 70
■Chapter 5: Object Tools .......................................................................................71
PHP and Packages ........................................................................................................ 71
PHP Packages and Namespaces..........................................................................................................71
Autoload ...............................................................................................................................................80

The Class and Object Functions.................................................................................... 81
Looking for Classes..............................................................................................................................82
Learning About an Object or Class.......................................................................................................83
Learning About Methods ......................................................................................................................84
Learning About Properties ...................................................................................................................85
Learning About Inheritance..................................................................................................................85
Method Invocation................................................................................................................................86

The Reflection API......................................................................................................... 87
Getting Started .....................................................................................................................................87
Time to Roll Up Your Sleeves ...............................................................................................................88
Examining a Class ..............................................................................................................................90
Examining Methods..............................................................................................................................91
Examining Method Arguments.............................................................................................................93
Using the Reflection API.......................................................................................................................94

Summary....................................................................................................................... 97
■Chapter 6: Objects and Design ............................................................................99
Defining Code Design.................................................................................................... 99
Object-Oriented and Procedural Programming........................................................... 100
Responsibility.....................................................................................................................................103
Cohesion ............................................................................................................................................104
Coupling .............................................................................................................................................104
Orthogonality......................................................................................................................................104

Choosing Your Classes................................................................................................ 105

vii

■ CONTENTS

Polymorphism ............................................................................................................. 106
Encapsulation ............................................................................................................. 107
Forget How to Do It ..................................................................................................... 108
Four Signposts ............................................................................................................ 109
Code Duplication ................................................................................................................................109
The Class Who Knew Too Much .........................................................................................................109
The Jack of All Trades........................................................................................................................109
Conditional Statements......................................................................................................................110

The UML ...................................................................................................................... 110
Class Diagrams ..................................................................................................................................110
Sequence Diagrams...........................................................................................................................117

Summary..................................................................................................................... 119
Part 3: Patterns ....................................................................................................121
■Chapter 7: What Are Design Patterns? Why Use Them?....................................123
What Are Design Patterns? ......................................................................................... 123
A Design Pattern Overview ......................................................................................... 125
Name..................................................................................................................................................125
The Problem.......................................................................................................................................125
The Solution .......................................................................................................................................126
Consequences....................................................................................................................................126

The Gang of Four Format ............................................................................................ 126
Why Use Design Patterns?.......................................................................................... 127
A Design Pattern Defines a Problem ..................................................................................................127
A Design Pattern Defines a Solution ..................................................................................................127
Design Patterns Are Language Independent......................................................................................127
Patterns Define a Vocabulary.............................................................................................................127
Patterns Are Tried and Tested ...........................................................................................................128
Patterns Are Designed for Collaboration............................................................................................128
Design Patterns Promote Good Design ..............................................................................................128

PHP and Design Patterns ............................................................................................ 129
Summary..................................................................................................................... 129

viii

■ CONTENTS

■Chapter 8: Some Pattern Principles ..................................................................131
The Pattern Revelation................................................................................................ 131
Composition and Inheritance ...................................................................................... 132
The Problem.......................................................................................................................................132
Using Composition .............................................................................................................................135

Decoupling .................................................................................................................. 137
The Problem.......................................................................................................................................137
Loosening Your Coupling ...................................................................................................................139

Code to an Interface, Not to an Implementation ......................................................... 141
The Concept That Varies ............................................................................................. 142
Patternitis.................................................................................................................... 143
The Patterns................................................................................................................ 143
Patterns for Generating Objects.........................................................................................................143
Patterns for Organizing Objects and Classes .....................................................................................143
Task-Oriented Patterns ......................................................................................................................143
Enterprise Patterns ............................................................................................................................144
Database Patterns..............................................................................................................................144

Summary..................................................................................................................... 144
■Chapter 9: Generating Objects ..........................................................................145
Problems and Solutions in Generating Objects........................................................... 145
The Singleton Pattern ................................................................................................. 149
The Problem.......................................................................................................................................149
Implementation ..................................................................................................................................150
Consequences....................................................................................................................................152

Factory Method Pattern .............................................................................................. 152
The Problem.......................................................................................................................................153
Implementation ..................................................................................................................................155
Consequences....................................................................................................................................157

Abstract Factory Pattern ............................................................................................. 157
The Problem.......................................................................................................................................158
Implementation ..................................................................................................................................159

ix

■ CONTENTS

Consequences....................................................................................................................................161
Prototype............................................................................................................................................162
The Problem.......................................................................................................................................163
Implementation ..................................................................................................................................163

But That’s Cheating! ................................................................................................... 166
Summary..................................................................................................................... 167
■Chapter 10: Patterns for Flexible Object Programming ....................................169
Structuring Classes to Allow Flexible Objects............................................................. 169
The Composite Pattern................................................................................................ 169
The Problem.......................................................................................................................................170
Implementation ..................................................................................................................................172
Consequences....................................................................................................................................175
Composite in Summary......................................................................................................................178

The Decorator Pattern................................................................................................. 179
The Problem.......................................................................................................................................179
Implementation ..................................................................................................................................181
Consequences....................................................................................................................................185

The Facade Pattern..................................................................................................... 185
The Problem.......................................................................................................................................185
Implementation ..................................................................................................................................186
Consequences....................................................................................................................................187

Summary..................................................................................................................... 187
■Chapter 11: Performing and Representing Tasks .............................................189
The Interpreter Pattern................................................................................................ 189
The Problem.......................................................................................................................................189
Implementation ..................................................................................................................................190
Interpreter Issues...............................................................................................................................197

The Strategy Pattern ................................................................................................... 198
The Problem.......................................................................................................................................198
Implementation ..................................................................................................................................199

The Observer Pattern .................................................................................................. 202

x

■ CONTENTS

Implementation ..................................................................................................................................204

The Visitor Pattern ...................................................................................................... 210
The Problem.......................................................................................................................................210
Implementation ..................................................................................................................................211
Visitor Issues......................................................................................................................................215

The Command Pattern ................................................................................................ 216
The Problem.......................................................................................................................................216
Implementation ..................................................................................................................................216

Summary..................................................................................................................... 220
■Chapter 12: Enterprise Patterns........................................................................221
Architecture Overview................................................................................................. 221
The Patterns.......................................................................................................................................222
Applications and Layers.....................................................................................................................222

Cheating Before We Start............................................................................................ 225
Registry..............................................................................................................................................225
Implementation ..................................................................................................................................226

The Presentation Layer ............................................................................................... 235
Front Controller ..................................................................................................................................235
Application Controller.........................................................................................................................245
Page Controller ..................................................................................................................................257
Template View and View Helper ........................................................................................................262

The Business Logic Layer ........................................................................................... 264
Transaction Script..............................................................................................................................265
Domain Model ....................................................................................................................................269

Summary..................................................................................................................... 273
■Chapter 13: Database Patterns .........................................................................275
The Data Layer ............................................................................................................ 275
Data Mapper ............................................................................................................... 275
The Problem.......................................................................................................................................276
Implementation ..................................................................................................................................276
Consequences....................................................................................................................................287

xi

■ CONTENTS

Identity Map ................................................................................................................ 288
The Problem.......................................................................................................................................288
Implementation ..................................................................................................................................289
Consequences....................................................................................................................................291

Unit of Work ................................................................................................................ 291
The Problem.......................................................................................................................................292
Implementation ..................................................................................................................................292
Consequences....................................................................................................................................296
Lazy Load ...........................................................................................................................................296
The Problem.......................................................................................................................................296
Implementation ..................................................................................................................................297
Consequences....................................................................................................................................298

Domain Object Factory................................................................................................ 298
The Problem.......................................................................................................................................298
Implementation ..................................................................................................................................299
Consequences....................................................................................................................................300

The Identity Object ...................................................................................................... 301
The Problem.......................................................................................................................................301
Implementation ..................................................................................................................................302
Consequences....................................................................................................................................307

The Selection Factory and Update Factory Patterns ................................................... 307
The Problem.......................................................................................................................................307
Implementation ..................................................................................................................................307
Consequences....................................................................................................................................311

What’s Left of Data Mapper Now? .............................................................................. 311
Summary..................................................................................................................... 313
Part 4: Practice ....................................................................................................315
■Chapter 14: Good (and Bad) Practice ................................................................317
Beyond Code ............................................................................................................... 317
Borrowing a Wheel..................................................................................................... 317
Playing Nice ................................................................................................................ 319

xii

■ CONTENTS

Giving Your Code Wings .............................................................................................. 319
Documentation............................................................................................................ 320
Testing ........................................................................................................................ 321
Continuous Integration................................................................................................ 322
Summary..................................................................................................................... 322
■Chapter 15: An Introduction to PEAR and Pyrus ...............................................323
What Is PEAR?............................................................................................................. 323
Phar Out with Pyrus .................................................................................................... 324
Installing a Package................................................................................................... 326
PEAR Channels...................................................................................................................................327

Using a PEAR Package................................................................................................ 329
Handling PEAR Errors.........................................................................................................................331

Creating Your Own PEAR Package .............................................................................. 334
package.xml.......................................................................................................................................334
Package Elements..............................................................................................................................334
The contents Element .....................................................................................................................336
Dependencies ....................................................................................................................................339
Tweaking Installation with phprelease ...........................................................................................340
Preparing a Package for Shipment ....................................................................................................341
Setting Up Your Own Channel ............................................................................................................341

Summary..................................................................................................................... 346
■Chapter 16: Generating Documentation with phpDocumentor..........................347
Why Document?.......................................................................................................... 347
Installation .................................................................................................................. 348
Generating Documentation ......................................................................................... 349
DocBlock Comments................................................................................................... 350
Documenting Classes ................................................................................................. 352
File-Level Documentation ........................................................................................... 353
Documenting Properties ............................................................................................. 353
Documenting Methods................................................................................................ 355

xiii

■ CONTENTS

Creating Links in Documentation................................................................................ 356
Summary..................................................................................................................... 359
■Chapter 17: Version Control with Subversion ...................................................361
Why Use Version Control?........................................................................................... 361
Getting Subversion...................................................................................................... 362
Configuring a Subversion Repository.......................................................................... 363
Creating a Repository.........................................................................................................................363

Beginning a Project..................................................................................................... 364
Updating and Committing ........................................................................................... 368
Adding and Removing Files and Directories ............................................................... 371
Adding a File ......................................................................................................................................371
Removing a File .................................................................................................................................372
Adding a Directory .............................................................................................................................372
Removing Directories.........................................................................................................................373

Tagging and Exporting a Release ............................................................................... 373
Tagging a Project ...............................................................................................................................373
Exporting a Project.............................................................................................................................374

Branching a Project..................................................................................................... 374
Summary..................................................................................................................... 378
■Chapter 18: Testing with PHPUnit .....................................................................379
Functional Tests and Unit Tests.................................................................................. 379
Testing by Hand .......................................................................................................... 380
Introducing PHPUnit .................................................................................................... 382
Creating a Test Case ..........................................................................................................................382
Assertion Methods .............................................................................................................................383
Testing Exceptions .............................................................................................................................384
Running Test Suites ...........................................................................................................................385
Constraints.........................................................................................................................................386
Mocks and Stubs ...............................................................................................................................388
Tests Succeed When They Fail ..........................................................................................................391

xiv

■ CONTENTS

Writing Web Tests....................................................................................................... 394
Refactoring a Web Application for Testing.........................................................................................394
Simple Web Testing ...........................................................................................................................397
Introducing Selenium .........................................................................................................................398

A Note of Caution ........................................................................................................ 403
Summary..................................................................................................................... 405
■Chapter 19: Automated Build with Phing ..........................................................407
What Is Phing? ............................................................................................................ 407
Getting and Installing Phing ........................................................................................ 408
Composing the Build Document.................................................................................. 408
Targets ...............................................................................................................................................410
Properties...........................................................................................................................................412
Types..................................................................................................................................................416
Tasks..................................................................................................................................................421

Summary.............................................................................................................