This is a presentation for the November WordPress Melbourne meetup. It shows how to modify your main WordPress query the right way, using the pre_get_posts hook, rather than using query_posts() or even WP_Query().

1. WordPress Queries
-the right way
Anthony Hortin
#wpmelb @maddisondesigns

2. How you’re probably querying
query_posts()
get_posts()
new WP_Query()

3. You’re doing it wrong!

4. The Loop
if ( have_posts() ) :
while ( have_posts() ) :
the_post();
endwhile;
endif;

5. The Loop
if ( have_posts() )
// Determines if there’s anything to iterate
while ( have_posts() ) :
the_post();
endwhile;
endif;

6. The Loop
if ( have_posts() )
while ( have_posts() ) :
// Sets up globals & continues iteration
the_post();
endwhile;
endif;

7. Anatomy of a WordPress Page
The Main Query

8. wp-blog-header.php
// Loads the WordPress bootstrap
// ie. Sets the ABSPATH constant.
// Loads the wp-config.php file etc.
require_once( dirname(__FILE__) . '/wp-load.php' );
wp();
// Decide which template files to load
// ie. archive.php, index.php etc
require_once( ABSPATH . WPINC . '/template-loader.php' );

9. wp-blog-header.php
// Loads the WordPress bootstrap
// ie. Sets the ABSPATH constant.
// Loads the wp-config.php file etc.
require_once( dirname(__FILE__) . '/wp-load.php' );
wp();
// Decide which template files to load
// ie. archive.php, index.php etc
require_once( ABSPATH . WPINC . '/template-loader.php' );

10. wp-blog-header.php
// Loads the WordPress bootstrap
// ie. Sets the ABSPATH constant.
// Loads the wp-config.php file etc.
require_once( dirname(__FILE__) . '/wp-load.php' );
wp();
// Decide which template files to load
// ie. archive.php, index.php etc
require_once( ABSPATH . WPINC . '/template-loader.php' );

11. wp-blog-header.php
// Loads the WordPress bootstrap
// ie. Sets the ABSPATH constant.
// Loads the wp-config.php file etc.
require_once( dirname(__FILE__) . '/wp-load.php' );
// Does ALL THE THINGS!
wp();
// Decide which template files to load
// ie. archive.php, index.php etc
require_once( ABSPATH . WPINC . '/template-loader.php' );

12. What is wp()?
wp();
- Parses the URL & runs it through WP_Rewrite
- Sets up query variables for WP_Query
- Runs the query

13. What is wp()?
wp();
- Parses the URL & runs it through WP_Rewrite
- Sets up query variables for WP_Query
- Runs the query

14. What is wp()?
wp();
- Parses the URL & runs it through WP_Rewrite
- Sets up query variables for WP_Query
- Runs the query

15. What is wp()?
wp();
- Parses the URL & runs it through WP_Rewrite
- Sets up query variables for WP_Query
- Runs the query

16. So, what does this mean?

17. It means...
Before the theme is even loaded,
WordPress already has your Posts!

18. Mind == Blown!

19. In the bootstrap
$wp_the_query = new WP_Query();
$wp_query =& $wp_the_query;

20. In the bootstrap
// Holds the real main query.
// It should never be modified
$wp_the_query
// A live reference to the main query
$wp_query

21. In the bootstrap
// Holds the real main query.
// It should never be modified
$wp_the_query
// A live reference to the main query
$wp_query

22. Back to our queries...

23. query_posts()
get_posts()
new WP_Query()
All three create new WP_Query objects

24. query_posts()
goes one step further though

25. query_posts()
function &query_posts($query) {
unset($GLOBALS['wp_query']);
$GLOBALS['wp_query'] = new WP_Query();
return $GLOBALS['wp_query']->query($query);
}

26. query_posts()
function &query_posts($query) {
// Destroys the Global $wp_query variable!
unset($GLOBALS['wp_query']);
$GLOBALS['wp_query'] = new WP_Query();
return $GLOBALS['wp_query']->query($query);
}

27. query_posts()
function &query_posts($query) {
unset($GLOBALS['wp_query']);
// Creates new $wp_query variable
$GLOBALS['wp_query'] = new WP_Query();
return $GLOBALS['wp_query']->query($query);
}

28. I’m sure you’ve all done this...
get_header();
query_posts( 'cat=-1,-2,-3' );
while( have_posts() ) :
the_post();
endwhile;
wp_reset_query();
get_footer();

29. That’s running 2* queries!

30. That’s running 2* queries!
It’s running the query WordPress
thinks you want.
It’s then running your new query
you actually want.

31. * In actual fact, WP_Query
doesn’t just run one query.
It runs four!
So, that means your template
is actually running eight queries!

32. Don’t forget to reset
// Restores the $wp_query reference to $wp_the_query
// Resets the globals
wp_reset_query();
// Resets the globals
wp_reset_postdata();

33. There’s a better way

34. Say hello to pre_get_posts
[From the Codex]
The pre_get_posts action gives developers
access to the $query object by reference.
(any changes you make to $query are made
directly to the original object)

35. Say hello to pre_get_posts
What this means is we can change our
main query before it’s run

36. pre_get_posts
pre_get_posts fires for every post query:
— get_posts()
— new WP_Query()
— Sidebar widgets
— Admin screen queries
— Everything!

37. How do we use it?

38. In functions.php
[example 1]
function my_pre_get_posts( $query ) {
// Check if the main query and home and not admin
if ( $query->is_main_query() && is_home() && !is_admin() ) {
// Display only posts that belong to a certain Category
$query->set( 'category_name', 'fatuity' );
// Display only 3 posts per page
$query->set( 'posts_per_page', '3' );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

39. In functions.php
[example 1]
function my_pre_get_posts( $query ) {
// Check if the main query and home and not admin
if ( $query->is_main_query() && is_home() && !is_admin() ) {
// Display only posts that belong to a certain Category
$query->set( 'category_name', 'fatuity' );
// Display only 3 posts per page
$query->set( 'posts_per_page', '3' );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

40. In functions.php
[example 1]
function my_pre_get_posts( $query ) {
// Check if the main query and home and not admin
if ( $query->is_main_query() && is_home() && !is_admin() ) {
// Display only posts that belong to a certain Category
$query->set( 'category_name', 'fatuity' );
// Display only 3 posts per page
$query->set( 'posts_per_page', '3' );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

41. In functions.php
[example 1]
function my_pre_get_posts( $query ) {
// Check if the main query and home and not admin
if ( $query->is_main_query() && is_home() && !is_admin() ) {
// Display only posts that belong to a certain Category
$query->set( 'category_name', 'fatuity' );
// Display only 3 posts per page
$query->set( 'posts_per_page', '3' );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

42. In functions.php
[example 1]
function my_pre_get_posts( $query ) {
// Check if the main query and home and not admin
if ( $query->is_main_query() && is_home() && !is_admin() ) {
// Display only posts that belong to a certain Category
$query->set( 'category_name', 'fatuity' );
// Display only 3 posts per page
$query->set( 'posts_per_page', '3' );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

43. In functions.php
[example 2]
function my_pre_get_posts( $query ) {
// Check if the main query and movie CPT archive and not admin
if($query->is_main_query() && is_post_type_archive('movie') && !is_admin()){
// Display only posts from a certain taxonomies
$query->set( 'tax_query', array(
array( 'taxonomy' => 'genre',
'field' => 'slug',
'terms' => array ( 'fantasy', 'sci-fi' )
)
) );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

44. In functions.php
[example 2]
function my_pre_get_posts( $query ) {
// Check if the main query and movie CPT archive and not admin
if($query->is_main_query() && is_post_type_archive('movie') && !is_admin()){
// Display only posts from a certain taxonomies
$query->set( 'tax_query', array(
array( 'taxonomy' => 'genre',
'field' => 'slug',
'terms' => array ( 'fantasy', 'sci-fi' )
)
) );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

45. In functions.php
[example 2]
function my_pre_get_posts( $query ) {
// Check if the main query and movie CPT archive and not admin
if($query->is_main_query() && is_post_type_archive('movie') && !is_admin()){
// Display only posts from a certain taxonomies
$query->set( 'tax_query', array(
array( 'taxonomy' => 'genre',
'field' => 'slug',
'terms' => array ( 'fantasy', 'sci-fi' )
)
) );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

46. In functions.php
[example 2]
function my_pre_get_posts( $query ) {
// Check if the main query and movie CPT archive and not admin
if($query->is_main_query() && is_post_type_archive('movie') && !is_admin()){
// Display only posts from a certain taxonomies
$query->set( 'tax_query', array(
array( 'taxonomy' => 'genre',
'field' => 'slug',
'terms' => array ( 'fantasy', 'sci-fi' )
)
) );
return;
}
}
// Add our function to the pre_get_posts hook
add_action( 'pre_get_posts', 'my_pre_get_posts' );

47. Remember...
Do:
— Use pre_get_posts
— Check if it’s the main query by using is_main_query()
— Check it’s not an admin query by using is_admin()
— Check for specific templates using is_home(), etc..
— Set up your query using same parameters as WP_Query()
Don’t:
— Use query_posts()
unless you have a very good reason AND you use wp_reset_query()
( if you really need a secondary query, use new WP_Query() )

48. References
// You Don’t Know Query - Andrew Nacin
http://wordpress.tv/2012/06/15/andrew-nacin-wp_query
http://www.slideshare.net/andrewnacin/you-dont-know-query-wordcamp-portland-2011
// Make sense of WP Query functions
http://bit.ly/wpsequery
// Querying Posts Without query_posts
http://developer.wordpress.com/2012/05/14/querying-posts-without-query_posts
// pre_get_posts on the WordPress Codex
http://codex.wordpress.org/Plugin_API/Action_Reference/pre_get_posts
// Example code on Github
https://github.com/maddisondesigns/wpmelb-nov

49. That’s all folks!☺
Thanks! Questions?