This is a slightly modified version of the talk I gave at the London Wordpress meetup. I'm putting it up here a) for people who were taking notes last night and b) to shame me into putting a polished version up here for people who couldn't make it. thanks for @folletto for providing the graphics that split up the endless code snippets.

1. Getting to The Loop
working with themes is commonplace, but
how WP gets there is still seen as magic.
it doesn’t need to be that hard. Here’s how it
gets there...

2. Load
Plugins
DB
Template
The Loop

3. Load in files for a bootstrap phase
set up Plugins
turn the request URL into a DB query
choose a Template
start The Loop

4. Load

5. important files for this
step:
• index.php
• blog-header.php
• wp-load.php
• wp-settings.php

6. index.php
<?php
/**
* Front to the WordPress application. This file doesn't
do anything, but loads
* wp-blog-header.php which does and tells WordPress to
load the theme.
*/
define('WP_USE_THEMES', true);
/** Loads the WordPress Environment and Template */
require('./wp-blog-header.php');
?>

7. blog-header.php
<?php
/**
* Loads the WordPress environment and template.
*/
require_once( dirname(__FILE__) . '/wp-load.php' );
wp();
require_once( ABSPATH . WPINC . '/template-loader.php' );
}
?>

8. wp-load.php
<?php
/** Define ABSPATH as this files directory */
define( 'ABSPATH', dirname(__FILE__) . '/' );
if ( file_exists( ABSPATH . 'wp-config.php') ) {
require_once( ABSPATH . 'wp-config.php' );
} else {
wp_die("There doesn't seem to be a wp-config.php file.
I need this before we can get started. );
}
?>

9. wp-load.php
<?php
/** Define ABSPATH as this files directory */
define( 'ABSPATH', dirname(__FILE__) . '/' );
if ( file_exists( ABSPATH . 'wp-config.php') ) {
require_once( ABSPATH . 'wp-config.php' );
} else {
wp_die("There doesn't seem to be a wp-config.php file.
I need this before we can get started. );
}
?>

10. wp-config.php
<?php
//
/** The name of the database for WordPress */
define('DB_NAME', 'database_name_here');
/** MySQL database username */
define('DB_USER', 'username_here');
/** MySQL database password */
define('DB_PASSWORD', 'password_here');
/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');

11. wp-config.php
<?php
//
/** The name of the database for WordPress */
define('DB_NAME', 'database_name_here');
/** MySQL database username */
define('DB_USER', 'username_here');
/** MySQL database password */
define('DB_PASSWORD', 'password_here');
/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');

12. wp-settings.php
<?php
// Load early WordPress files.
require( ABSPATH . WPINC . '/compat.php' );
require( ABSPATH . WPINC . '/functions.php' );
require( ABSPATH . WPINC . '/class-wp.php' );
require( ABSPATH . WPINC . '/class-wp-error.php' );
require( ABSPATH . WPINC . '/plugin.php' );
// Load most of WordPress.
require( ABSPATH . WPINC . '/class-wp-ajax-response.php' );
require( ABSPATH . WPINC . '/formatting.php' );
require( ABSPATH . WPINC . '/query.php' );

13. wp-settings.php
<?php
// Make taxonomies and posts available to plugins and themes.
create_initial_taxonomies();
create_initial_post_types();
// Load active plugins.
foreach ( wp_get_active_and_valid_plugins() as $plugin ) {
include_once( $plugin );
}
do_action( 'plugins_loaded' );
do_action( 'setup_theme' );
do_action( 'after_setup_theme' );
do_action( 'wp_loaded' );
?>

14. Plugins

15. plugins, hooks, actions
add_action( ‘hook’, ‘function’) do_action(‘admin_notices’)
apply_filter
add_filter(‘hook’, $template)
(‘template_redirect’)

16. loading plugins

17. hello_dolly_example.php
// Fetch a random song lyric and add it to the page
function hello_dolly() {
$chosen = hello_dolly_get_lyric();
echo "<p id='dolly'>$chosen</p>";
}
// Now we set that function up to execute when the
admin_notices action is called
add_action( 'admin_notices', 'hello_dolly' );

18. loading plugins

19. DB

20. turn the request URL
into a DB query
• from - http://mysite.com/category/something
• to - WP_Query(category=‘something’)

21. class-wp.php
<?php
class WP {
function main($query_args = '') {
$this->init();
$this->parse_request($query_args);
$this->send_headers();
$this->query_posts();
$this->handle_404();
$this->register_globals();
do_action_ref_array('wp', array(&
$this));
}

22. class-wp.php
<?php
class WP {
function main($query_args = '') {
$this->init();
$this->parse_request($query_args);
$this->send_headers();
$this->query_posts();
$this->handle_404();
$this->register_globals();
do_action_ref_array('wp', array(&
$this));
}

23. Template

24. blog-header.php
<?php
/**
* Loads the WordPress environment and template.
*/
require_once( dirname(__FILE__) . '/wp-load.php' );
wp();
require_once( ABSPATH . WPINC . '/template-loader.php' );
}
?>

25. blog-header.php
<?php
/**
* Loads the WordPress environment and template.
*/
require_once( dirname(__FILE__) . '/wp-load.php' );
wp();
require_once( ABSPATH . WPINC . '/template-loader.php' );
}
?>

26. template-loader.php
<?php
// (abridged version)
if ( is_single() && $template = get_single_template() ) :
elseif ( is_page() && $template = get_page_template() ) :
elseif ( is_category() && $template = get_category_template() ) :
elseif ( is_tag() && $template = get_tag_template() ) :
elseif ( is_author() && $template = get_author_template() ) :
elseif ( is_date() && $template = get_date_template() ) :
elseif ( is_archive() && $template = get_archive_template() ) :

27. The Loop

28. Start The Loop
• we now have our template, chosen inside
template-loader.php
• we now have our query results from wp() in
wp-blog-header.php
• now hand these over to The Loop - thanks
Keith!

29. Phew! Thank you!
c@headshift.com
@mrchrisadams