1. WordCamp Austin 2012

2. Chris Olbekson
WordPress Consultant
C3M Digital
@Chris_Olbekson on Twitter
chris@c3mdigital.com
WordCamp Austin 2012

3. The Query, The Whole
Query, & Nothing But
$the_query

4. What is the query?

5. What is the query?
The Loop

6. What is the query?
The Loop
while( have_posts() ): the_post();
the_content();
endwhile;

7. What is the query?
WP_Query class

8. What is the query?
$wp_query object

9. class WP_Query

10. $wp_query object
The WP Class gives the $wp_query object
information that defines the current
request.

11. class WP_Query
$wp_query object
The WP Class gives the $wp_query object
information that defines the current
request.
$wp_query determines the query based on
that information and fetches the
requested posts

12. class WP_Query
class WP {
function main() {
$this->init();
$this->parse_request();
$this->query_posts();
$this->handle_404();
$this->register_globals()
$wp_query object

13. class WP_Query
Properties
$query, $query_vars, $posts, $post_count,
$current_post, $queried_object_id, etc...
Booleans: is_single(), is_category(), is_paged(),
etc...

14. class WP_Query
Methods
init(), parse_query(), set( $query_var, $value ),
have_posts(), rewind_posts() etc...

15. class WP_Query
Interacting with WP_Query

16. class WP_Query
Interacting with WP_Query
Before the loop
Altering the query, filters

17. class WP_Query
Interacting with WP_Query
During the loop
Conditionals and template tags,
secondary queries, get_sidebar(), more
secondary queries, get_footer().

18. How do we Query?

19. How do we Query?
query_posts() alters the main query

20. How do we Query?
query_posts() alters the main query
new WP_Query() use for secondary queries

21. How do we Query?
query_posts() alters the main query
new WP_Query() use for secondary queries
WP_Query - returns an array of post objects

22. How do we Query?
query_posts() alters the main query
new WP_Query() use for secondary queries
WP_Query - returns an array of post objects
get_posts() use for secondary queries

23. How do we Query?
query_posts() alters the main query
new WP_Query() use for secondary queries
WP_Query - returns an array of post objects
get_posts() use for secondary queries
get_posts() - wrapper for a separate instance of WP_Query
returns an array of post objects

24. How do we Query?
query_posts() alters the main query
new WP_Query() use for secondary queries
WP_Query - returns an array of post objects
get_posts() use for secondary queries
get_posts() - wrapper for a separate instance of WP_Query
returns an array of post objects
$wpdb->roll your own

25. How do we Query?
query_posts() alters the main query
new WP_Query() use for secondary queries
WP_Query - returns an array of post objects
get_posts() use for secondary queries
get_posts() - wrapper for a separate instance of WP_Query
returns an array of post objects
$wpdb->roll your own
$wpdb uses the wpdb class to execute any SQL query on the
WordPress database

26. Secondary Loops

27. Secondary Loops
new WP_Query()
$my_query = new WP_Query();
while( $my_query->have_posts() ):
$my_query->the_post();
// do stuff
endwhile;

28. Secondary Loops
get_posts()
get_posts() uses the WP_Query class to
fetch an array of post objects
$post->post_content, $post->post_title
etc...

29. Secondary Loops
get_posts()
$post = get_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
! foreach( $posts as $post ) {
echo $post->post_title;
echo apply_filters( ‘the_content’, $post->post_content );
}

30. Secondary Loops
get_posts()
$post = get_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
/**
*
* To make post template tags ie: the_content()
* available when using get_posts() call the
* internal function setup_postdata() with the
* the $post array as its argument
*
*/

31. Secondary Loops
get_posts()
$post = get_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
foreach( $posts as $post ) {
! setup_postdata( $post );
the_title();
the_content();
}

32. Secondary Loops
get_posts()
$post = get_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
**/
*
* After looping through a separate query,
* wp_reset_postdata() restores the $post global
* to the current post in the main query
*
*/

33. Secondary Loops
get_posts()
$post = get_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
foreach( $posts as $post ) {
! setup_postdata( $post );
the_title();
the_content();
}
wp_reset_postdata();

34. query_posts()

35. query_posts()
query_posts() sets up The Loop with
query parameters. It also overrides the
current WordPress Loop.

36. query_posts()
query_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
if ( have_posts() ) : while ( have_posts() : the_post();
the_title();
the_content();
endwhile; endif;

37. query_posts()
query_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
**/
* If you use query_posts() you HAVE to use
* wp_reset_query() to restore the $post globals
*
*/

38. query_posts()
query_posts( array(
‘posts_per_page’ => 7
! ! ‘cat’ => -3,
));
if ( have_posts() ) : while ( have_posts() : the_post();
the_title();
the_content();
endwhile; endif; wp_reset_query();

39. query_posts()
query_posts() alters destroys the
global $wp_query variables
/**
*
* This will cause WordPress to run the query it
* thought you wanted and the one you’re actually going
* to use.
*
* breaks widgets
* pagination breaks
* conditional tags will not work
* and more...
*
*/

40. When should we use
query_posts()?

41. query_posts()
The Problem with query_posts() is that it
is always a secondary loop that tries to
be the main one and fails miserably.

42. When should we use
query_posts()?

43. When should we use
query_posts()?
NEVER USE query_posts()

44. When should we use
query_posts()?
NEVER USE query_posts()
query_posts()

45. What if I want to alter
the query?

46. pre_get_posts()

47. pre_get_posts()
pre_get_posts fires every time WordPress
fetches posts from the database.
nav menus, new wp_query, query_posts,
get_posts, that slider plugin your client
installed, everything.

48. What if I only want to
alter the main query?

49. is_main_query()

50. is_main_query()
function alter_query( $query ) {
! if ( $query->is_main_query() && $query->is_home() )
! ! $query->set( ‘cat’, ‘-3’ );
}
add_action( ‘pre_get_posts’, ‘alter_query’ );

51. What happens when we
run a query?

52. What happens when we
run a query?
WordPress actually runs 4 SQL queries
every time a query is run

53. $my_query = new WP_Query();
while( $my_query->have_posts() ):
$my_query->the_post();

54. $my_query = new WP_Query();
while( $my_query->have_posts() ):
$my_query->the_post();
1)Gets the posts:
SELECT SQL_CALC_FOUND_ROWS...
FROM wp_post LIMIT 0, 10

55. $my_query = new WP_Query();
while( $my_query->have_posts() ):
$my_query->the_post();
1)Gets the posts:
SELECT SQL_CALC_FOUND_ROWS...
FROM wp_post LIMIT 0, 10
2)Counts the posts for pagination:
SELECT FOUND_ROWS()

56. $my_query = new WP_Query();
while( $my_query->have_posts() ):
$my_query->the_post();
1)Gets the posts:
SELECT SQL_CALC_FOUND_ROWS...
FROM wp_post LIMIT 0, 10
2)Counts the posts for pagination:
SELECT FOUND_ROWS()
3)Gets all the metadata:
SELECT post_id, meta_key, meta_value FROM
wp_postmeta WHERE post_id IN...

57. $my_query = new WP_Query();
while( $my_query->have_posts() ):
$my_query->the_post();
1)Gets the posts:
SELECT SQL_CALC_FOUND_ROWS...
FROM wp_post LIMIT 0, 10
2)Counts the posts for pagination:
SELECT FOUND_ROWS()
3)Gets all the metadata:
SELECT post_id, meta_key, meta_value FROM
wp_postmeta WHERE post_id IN...
4)Gets all the terms
SELECT… AS… INNER JOIN wp_term_taxonomy
AS... INNER JOIN wp_term_relationships
AS... ON... IN...

58. What if I don’t need
pagination, meta, or
terms?

59. What if I don’t need
pagination, meta, or
terms?
You can selectively turn these off

60. What if I don’t need
pagination, meta, or
terms?
You can selectively turn these off
$my_query = new WP_Query( array(
‘no_found_rows’ = true,
‘update_post_meta_cache’ => false,
‘update_post_term_cache’ => false,
) );

61. <review>
$wp_query is always the main query
if you use query_posts(), $wp_query now holds the query
you just created.

62. <review>
$wp_query is always the main query
if you use query_posts(), $wp_query now holds the query
you just created.
Use pre_get_posts() when you need to alter the main query.
It’s cleaner the “right” way to do it and your clients and
fellow developers will love you.

63. <review>
$wp_query is always the main query
if you use query_posts(), $wp_query now holds the query
you just created.
Use pre_get_posts() when you need to alter the main query.
It’s cleaner the “right” way to do it and your clients and
fellow developers will love you.
For secondary queries - custom sliders, sidebars, etc...
use get_posts() or create a new WP_Query

64. <review>
$wp_query is always the main query
if you use query_posts(), $wp_query now holds the query
you just created.
Use pre_get_posts() when you need to alter the main query.
It’s cleaner the “right” way to do it and your clients and
fellow developers will love you.
For secondary queries - custom sliders, sidebars, etc...
use get_posts() or create a new WP_Query
If you call the_post(), or set_up_postdata() use
wp_reset_postdata(). If you have to use query_posts() use
wp_reset_query().

65. </review>

66. questions?