1. WordCamp Pune 2013

2. Savita Soni, co-founder AmiWorks & chief-poet for WPoets
Twitter @savitas

3. Power of WP_Query

4. Ways to fetch posts & related data
• query_posts()
• new WP_Query()
• get_posts()
• $wpdb global db object

5. query_posts()

6. How query_posts() looks
query_posts( $args );
while ( have_posts() ) :
the_post();
//the_title(), the_ID(), the_permalink() etc..
endwhile;
// Reset Query
wp_reset_query();

7. new WP_Query()

8. How WP_Query() looks
// The Query
$the_query = new WP_Query( $args );
// The Loop
while ( $the_query->have_posts() ) :
$the_query->the_post();
echo '<li>' . get_the_title() . '</li>';
endwhile;
wp_reset_postdata();

9. get_posts()

10. How get_posts() looks
<?php
global $post;
$args = array( 'numberposts' => 5, 'offset'=> 1, 'category' => 1 );
$myposts = get_posts( $args );
foreach( $myposts as $post ) :
setup_postdata($post); ?>
<li><a href="<?php the_permalink(); ?>">
<?php the_title(); ?></a></li>
<?php endforeach;
?>

11. This all we already know?

12. So lets see something which we may not know...

13. Conditional tags
is_author()
is_home()
is_archive()
we know this as well and use them frequently…

14. But have you seen this?
$wp_query = new WP_Query( $args );
$wp_query->is_author()
$wp_query->is_home()
$wp_query->is_archive()
Yes every query object has its own methods

15. so we can do this as well
$my_query = new WP_Query( $args );
while( $my_query->have_posts() ):
$my_query->the_post();
if( $my_query->is_author()){
// do something for author
}
endwhile;
wp_reset_postdata();

16. why we always needs to call
wp_reset_query()
wp_reset_postdata();
with query_posts() or WP_Query()

17. because when we do this
query_posts( 'cat=5');
while ( have_posts() ) :
the_post();
//the_title(), the_ID(), the_permalink() etc..
endwhile;
We have altered the main query...

18. How?
global $wp_query; //this is the main query object
Do anyone know this?
$wp_the_query
So the real main query object $wp_the_query
and $wp_query is the live copy of $wp_the_query

19. it is something like
$wp_the_query = new WP_Query();
$wp_query = &$wp_the_query;

20. when we call query_posts(), it works like this
function query_posts($query) {
$GLOBALS['wp_query'] = new WP_Query();
return $GLOBALS['wp_query']->query($query);
}

21. and when we call wp_reset_query()
function wp_reset_query() {
$GLOBALS['wp_query'] = $GLOBALS['wp_the_query'];
wp_reset_postdata();
}

23. how many query(s) get called when we call
WP_Query()?
Is it running only one query with your passed
arguments????

24. it is running 4 queries
1. Select SQL_CALC_FOUND_ROWS....FROM wp_posts
limit 0,10
2. Select FOUND_ROWS();
3. Get all metadata attached to these posts.
4. Get all terms for these posts.

25. off some arguments selectively
new WP_Query(
array(
'no_found_rows' => false,
'update_post_meta_cache' => false,
'update_post_term_cache' => false
)
)

26. what if I need to modify the main query only?
Use pre_get_posts hook

27. function exclude_category( $query ) {
$query->set( 'cat', '-1,-1347' );
}
add_action( 'pre_get_posts', 'exclude_category' );

28. Now problem with this...
it gets called for every post query
get_posts()
WP_Query()
query_posts()

29. what if I just need it for home page query?
now $wp_the_query object will help
function exclude_category( $query ) {
global $wp_the_query;
if( $wp_the_query == $query
and $query->home()){
$query->set( 'cat', '-1,-1347' );
}
}
add_action( 'pre_get_posts', 'exclude_category' );

30. After WordPress 3.3 we have an awesome function
is_main_query()

31. So rather than writing
function exclude_category( $query ) {
global $wp_the_query;
//if( $wp_the_query == $query and $query->home())
if( $query->is_main_query() and $query->home()) {
$query->set( 'cat', '-1,-1347' );
}

32. Conclusion
 Try to avoid using query_posts()
 If query_posts() is used then reset it with
wp_reset_query()
 Use pre_get_posts hook to alter main query &
use it with is_main_query() condition tag

33. Thanks
Email: savita@amiworks.com
Twitter: @savitas