You Don't Know Query (WordCamp Netherlands 2012)

WordCamp Netherlands 2012

Andrew NacinCore Developer of WordPressand Tech Ninja at Audrey Capital@nacin on Twitternacin@wordpress.org

You Don’t Know Query

What do you know?

Conditional Tagsis_author( ), is_home( ), etc.

query_posts( )

Ways to queryquery_posts( )new WP_Query( )get_posts( )

The Loopwhile ( have_posts( ) ) : the_post( );endwhile;

A secondary loop$query = new WP_Query( … );while ( $query->have_posts( ) ) : $query->the_post( );endwhile;

An array of posts$result = get_posts( … );foreach ( $result as $post_obj ) {}

What don’t you know?

Every query object has itsown methodsis_author( ) is the same as calling$wp_query->is_author( )

function is_author( ) { global $wp_query; return $wp_query->is_author( );}

With the regular loopwhile ( have_posts( ) ) : the_post( ); if ( is_author( ) ) echo "An author query.";endwhile;

With the regular loopwhile ( have_posts( ) ) : the_post( ); if ( $wp_query->is_author( ) ) echo "An author query.";endwhile;

A secondary loop$query = new WP_Query( … );while ( $query->have_posts( ) ) : $query->the_post( ); if ( $query->is_author( ) ) echo "An author query.";endwhile;

If you do:$my_query = new WP_Query( $query );You can do:while ( $my_query->have_posts( ) ) : $my_query->the_post( );endwhile;wp_reset_postdata( );

Why do we call functions likewp_reset_postdata( ) andwp_reset_query( )?What about using query_posts( )?How can you alter a query? Howcan you alter the main query?

What is the main query,and why should I care?

wp-blog-header.php// Load the WordPress bootstraprequire ./wp-load.php;// Do magicwp( );// Decide which template ﬁles to loadrequire WPINC . /template-loader.php;

Lets look in the bootstrap:$wp_the_query = new WP_Query();$wp_query =& $wp_the_query;

Quick lesson on PHP references$a = 4;$b =& $a;$b = 2;var_dump( $a ); // int(2)$a = 6;var_dump( $b ); // int(6)

So:So the real main query is in$wp_the_query.And a live copy of it is stored in$wp_query.

wp-blog-header.php// Load the WordPress bootstraprequire ./wp-load.php;// Do magicwp( );// Decide which template ﬁles to loadrequire WPINC . /template-loader.php;

What is that wp( ) call?function wp( $query_vars = ) { global $wp; $wp->main( $query_vars );}

Holy $!@?, what justhappened?

In the bootstrap:$wp = new WP( );So theres a wp( ) function,and a WP class.

class WP { . . . function main( ) { $this->init( ); $this->parse_request( ); $this->send_headers( ); $this->query_posts( ); $this->handle_404( ); $this->register_globals( ); . . .

WP::parse_request( )— Parses the URL using WP_Rewrite— Sets up query variables for WP_QueryWP::query_posts( ) { global $wp_the_query; $wp_the_query->query( $this->query_vars );}

Boom.SELECT SQL_CALC_FOUND_ROWS wp_posts.*FROM wp_postsWHERE 1=1 AND wp_posts.post_type = post AND wp_posts.post_status = publishORDER BY wp_posts.post_date DESCLIMIT 0, 10

wp-blog-header.php// Load WordPress.require ./wp-load.php;// Parse what to query. Then query it.wp( );// Load the theme.require WPINC . /template-loader.php;

Before we get to the theme,we have your posts.Got it?

Then why do we do this?query_posts( author=-5 );get_header( );while( have_posts( ) ) : the_post( );endwhile;get_footer( );

Thats running 2* queries!One, the query WordPressthought we wanted.Two, this new one youreactually going to use.

* Actually, WP_Querydoesnt run just one query.It usually runs four.

1. Get me my posts: SELECT SQL_CALC_FOUND_ROWS … FROM wp_posts LIMIT 0, 102. How many posts exist? SELECT FOUND_ROWS( )3. Get all metadata for these posts.4. Get all terms for these posts.

(You can turn these oﬀ selectively…)$my_query = new WP_Query( array( no_found_rows => true, update_post_meta_cache => false, update_post_term_cache => false,) );

</aside>

PROTIP‘Measure twice, cut once’is bad for performance.

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You Don't Know Query (WordCamp Netherlands 2012)

by andrewnacin on Apr 01, 2012

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