OReilly Building Web Apps with WordPress

459 Pages·2014·14.12 MB·English

Building Web Apps with
WordPress
Brian Messenlehner and Jason Coleman
Building Web Apps with WordPress
by Brian Messenlehner and Jason Coleman
Copyright © 2014 Brian Messenlehner and Jason Coleman. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are
also available for most titles (http://my.safaribooksonline.com). For more information, contact our corporate/
institutional sales department: 800-998-9938 or [e-mail].
Editors: Meghan Blanchette and Allyson MacDonald Indexer: Ellen Troutman
Production Editor: Nicole Shelby Cover Designer: Randy Comer
Copyeditor: Charles Roumeliotis Interior Designer: David Futato
Proofreader: Amanda Kersey Illustrator: Rebecca Demarest
April 2014: First Edition
Revision History for the First Edition:
2014-04-07: First release
See http://oreilly.com/catalog/errata.csp?isbn=9781449364076 for release details.
Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of O’Reilly
Media, Inc. Building Web Apps with WordPress, the picture of a common iguana, and related trade dress
are trademarks of O’Reilly Media, Inc.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as
trademarks. Where those designations appear in this book, and O’Reilly Media, Inc. was aware of a trademark
claim, the designations have been printed in caps or initial caps.
While every precaution has been taken in the preparation of this book, the publisher and authors assume
no responsibility for errors or omissions, or for damages resulting from the use of the information contained
herein.
ISBN: 978-1-449-36407-6
[LSI]
Table of Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
1. Building Web Apps with WordPress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What Is a Website? 1
What Is an App? 1
What Is a Web App? 1
Features of a Web App 2
Why Use WordPress? 3
You Are Already Using WordPress 4
Content Management Is Easy with WordPress 4
User Management Is Easy and Secure with WordPress 4
Plugins 5
Flexibility Is Important 5
Frequent Security Updates 6
Cost 6
.NET App 6
WordPress App 7
Responses to Some Common Criticisms of WordPress 7
When Not to Use WordPress 10
You Plan to License or Sell Your Site’s Technology 10
There Is Another Platform That Will Get You “There” Faster 10
Flexibility Is NOT Important to You 11
Your App Needs to Be Highly Real Time 11
WordPress as an Application Framework 11
WordPress Versus MVC Frameworks 12
Anatomy of a WordPress App 15
What Is SchoolPress? 15
SchoolPress Runs on a WordPress Multisite Network 15
iii
The SchoolPress Business Model 15
Membership Levels and User Roles 16
Classes Are BuddyPress Groups 16
Assignments Are a Custom Post Type 16
Submissions Are a (Sub)CPT for Assignments 17
Semesters Are a Taxonomy on the Class CPT 17
Departments Are a Taxonomy on the Class CPT 17
SchoolPress Has One Main Custom Plugin 17
SchoolPress Uses a Few Other Custom Plugins 18
SchoolPress Uses the StartBox Theme Framework 18
2. WordPress Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
WordPress Directory Structure 21
Root Directory 22
/wp-admin 22
/wp-includes 22
/wp-content 22
WordPress Database Structure 23
wp_options 23
Functions Found in /wp-includes/option.php 24
wp_users 26
Functions Found in /wp-includes/… 27
wp_usermeta 30
wp_posts 34
Functions found in /wp-includes/post.php 34
wp_postmeta 38
Functions Found in /wp-includes/post.php 38
wp_comments 42
Functions Found in /wp-includes/comment.php 42
wp_commentsmeta 46
Functions Found in /wp-includes/comment.php 47
wp_links 49
wp_terms 50
Functions Found in /wp-includes/taxonomy.php 50
wp_term_taxonomy 53
/wp-includes/taxonomy.php 53
wp_term_relationships 54
Extending WordPress 55
3. Leveraging WordPress Plugins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
The GPLv2 License 58
Installing WordPress Plugins 58
iv | Table of Contents
Building Your Own Plugin 59
File Structure for an App Plugin 60
/adminpages/ 61
/classes/ 61
/css/ 62
/js/ 63
/images/ 63
/includes/ 63
/includes/lib/ 64
/pages/ 64
/services/ 65
/scheduled/ 65
/schoolpress.php 65
Add-Ons to Existing Plugins 66
Use Cases and Examples 66
The WordPress Loop 66
WordPress Global Variables 67
Action Hooks 77
Filters 77
Free Plugins 79
All in One SEO Pack 79
BadgeOS 79
Custom Post Type UI 80
Posts 2 Posts 80
Members 81
W3 Total Cache 81
Premium Plugins 81
Gravity Forms 81
Backup Buddy 81
WP All Import 82
Community Plugins 82
BuddyPress 82
4. Themes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Themes Versus Plugins 95
When Developing Apps 95
When Developing Plugins 96
When Developing Themes 97
The Template Hierarchy 97
Page Templates 99
Sample Page Template 99
Using Hooks to Copy Templates 102
Table of Contents | v
When to Use a Theme Template 103
Theme-Related WP Functions 103
Using locate_template in Your Plugins 104
Style.css 106
Versioning Your Theme’s CSS Files 106
Functions.php 108
Themes and Custom Post Types 108
Popular Theme Frameworks 108
WP Theme Frameworks 109
Non-WP Theme Frameworks 110
Creating a Child Theme for StartBox 111
Including Bootstrap in Your App’s Theme 111
Menus 113
Nav Menus 113
Dynamic Menus 114
Responsive Design 115
Device and Display Detection in CSS 115
Device and Feature Detection in JavaScript 116
Device Detection in PHP 118
Final Note on Browser Detection 122
Versioning CSS and JS Files 122
5. Custom Post Types, Post Metadata, and Taxonomies. . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Default Post Types and Custom Post Types 125
Page 125
Post 125
Attachment 126
Revisions 126
Nav Menu Item 126
Defining and Registering Custom Post Types 126
register_post_type( $post_type, $args ); 127
What Is a Taxonomy and How Should I Use It? 135
Taxonomies Versus Post Meta 135
Creating Custom Taxonomies 137
register_taxonomy( $taxonomy, $object_type, $args ) 137
register_taxonomy_for_object_type( $taxonomy, $object_type ) 141
Using Custom Post Types and Taxonomies in Your Themes and Plugins 141
The Theme Archive and Single Template Files 142
Good Old WP_Query and get_posts() 142
Metadata with CPTs 145
add_meta_box( $id, $title, $callback, $screen, $context, $priority,
$callback_args ) 146
vi | Table of Contents
Custom Wrapper Classes for CPTs 148
Extending WP_Post Versus Wrapping It 150
Why Use Wrapper Classes? 151
Keep Your CPTs and Taxonomies Together 151
Keep It in the Wrapper Class 152
Wrapper Classes Read Better 154
6. Users, Roles, and Capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Getting User Data 156
Add, Update, and Delete Users 158
Hooks and Filters 161
What Are Roles and Capabilities? 162
Checking a User’s Role and Capabilities 163
Creating Custom Roles and Capabilities 164
Extending the WP_User Class 166
Adding Registration and Profile Fields 168
Customizing the Users Table in the Dashboard 172
Plugins 174
Theme My Login 174
Hide Admin Bar from Non-Admins 174
Paid Memberships Pro 174
PMPro Register Helper 174
Members 175
7. Other WordPress APIs, Objects, and Helper Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Shortcode API 177
Shortcode Attributes 178
Nested Shortcodes 179
Removing Shortcodes 180
Other Useful Shortcode-Related Functions 180
Widgets API 181
Before You Add Your Own Widget 182
Adding Widgets 182
Defining a Widget Area 186
Embedding a Widget Outside of a Dynamic Sidebar 188
Dashboard Widgets API 188
Removing Dashboard Widgets 189
Adding Your Own Dashboard Widget 191
Settings API 193
Do You Really Need a Settings Page? 194
Could You Use a Hook or Filter Instead? 194
Use Standards When Adding Settings 196
Table of Contents | vii
Ignore Standards When Adding Settings 196
Rewrite API 197
Adding Rewrite Rules 198
Flushing Rewrite Rules 199
Other Rewrite Functions 200
WP-Cron 202
Adding Custom Intervals 203
Scheduling Single Events 204
Kicking Off Cron Jobs from the Server 204
Using Server Crons Only 206
WP Mail 206
Sending Nicer Emails with WordPress 207
File Header API 209
Adding File Headers to Your Own Files 211
Adding New Headers to Plugins and Themes 212
8. Secure WordPress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Why It’s Important 215
Security Basics 216
Update Frequently 216
Don’t Use the Username “admin” 216
Use a Strong Password 217
Examples of Bad Passwords 217
Examples of Good Passwords 218
Hardening Your WordPress Install 218
Don’t Allow Admins to Edit Plugins or Themes 218
Change Default Database Tables Prefix 218
Move wp-config.php 219
Hide Login Error Messages 220
Hide Your WordPress Version 220
Don’t Allow Logins via wp-login.php 221
Add Custom .htaccess Rules for Locking Down wp-admin 221
Backup Everything! 222
Scan Scan Scan! 223
Useful Security Plugins 223
Spam-Blocking Plugins 223
Backup Plugins 224
Scanner Plugins 224
Login and Password-Protection Plugins 225
Writing Secure Code 225
Check User Capabilities 225
Custom SQL Statements 226
viii | Table of Contents