WordPress London 16 May 2012 - You don’t know query

You Don’t Know Query

WordPress London
WordPress London
May 16, 2012

Scott Cariss aka Brady
Scott Cariss aka Brady
• Lead developer at Philosophy Design.
dd l hil h i

• Moderator at WordPress Answers
( p
(http://wordpress.stackexchange.com/)
p g )

• WordPress plugin developer and enthusiast
WordPress plugin developer and enthusiast

scott@philosophydesign
@ hil h d i
@l3rady on Twitter

You Don t Know Query
You Don’t Know Query

What do you know?
What do you know?

Conditional Tags
Conditional Tags
is_author(), is_home(), etc.

Who has ever heard of query_posts()?
Who has ever heard of query posts()?

Ways to query
Ways to query
query_posts()
new WP_Query()
new WP Query()
get_posts()

The loop
The loop
if( have_posts() )
while( have_posts() ):
while( have posts() ):
the_post();

endwhile();

What don t you know?
What don’t you know?

Every query object has its own
methods
is_author() is the same as calling
$wp_query >is_author()
$wp query‐>is author()

function is_author()
{
global $wp_query;

return $wp_query >is_author();
return $wp query‐>is author();
}

If you do:
$my_query new WP Query( $query );
$my query = new WP_Query( $query );

You can do:
while ( $my_query >have_posts( ) ) :
while ( $my query‐>have posts( ) ) :
$my_query‐>the_post( ); endwhile;
wp_reset_postdata( );

But why do we call things like
h d ll hi lik
wp_reset_postdata( ) and
p_ _p ()
wp_reset_query( )?

What about using query_posts( )?

How can you alter a query? What about
How can you alter a query? What about
the main query?

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

wp‐blog‐header.php
wp blog header php
// Load the WordPress bootstrap require
// d h d b i
dirname( __FILE__ ) . '/wp‐load.php';
( __ __ ) p p p

// Decide which template ﬁles to load
ABSPATH . WPINC . '/template‐loader.php';

Let s look in the bootstrap:
Let’s look in the bootstrap:
$wp_the_query = new WP_Query();
$wp_query & $wp_the_query;
$wp query =& $wp the query;

Quick lesson on PHP references
Quick lesson on PHP references
// References in PHP are a means to access the same variable content
// R f i PHP t th i bl t t
by different names.

$a = 4;
$b =& $a;

// It means that $a and $b now point to the same content.

$b = 2;
$b 2
var_dump( $a ); // int(2)

$a = 6;
var_dump( $b ); // int(6)

So:
The real main query is in
$wp_the_query.
$wp the query.

And a live copy of it is stored in
$wp_query
$wp query

wp blog header php
// Load the WordPress bootstrap require
// d h d b i
( __ __ ) p p p

// Do magic
// Do magic
wp();


What is that wp() call?
What is that wp() call?
function wp( $query_vars = '' )
{
global $wp;

$wp >main( $query_vars
$wp‐>main( $query vars );
}

Holy $!@?, what just happened?
Holy $!@? what just happened?

In the bootstrap:
In the bootstrap:
$wp = new WP()

So there’s a wp() function, and a WP class.

class WP
class WP
{
...
function main( )
f ()
{
$this‐>init( );
$this‐>parse_request( );
$this‐>send_headers( );
$
$this‐>query posts( );
q y_p ( );
$this‐>handle_404( );
$this‐>register_globals( );
}
. . .
}

WP::parse_request( )
WP t( )
Parses the URL using WP_Rewrite
Sets up query variables for WP_Query

WP::query_posts( )
{
global $wp_the_query;
$ p_
$wp the_q y q y( $
query‐>query( $this‐>query vars );
q y_ );
}

What do we get?
What do we get?
SELECT SQL_CALC_FOUND_ROWS
wp_posts. FROM
wp posts.* FROM
wp_posts WHERE 1=1
AND wp_posts.post_type = 'post‘
AND wp_posts.post_status = publish ORDER
AND wp posts post status = 'publish' ORDER
BY wp_posts.post_date DESC LIMIT 0, 10

wp blog header php
// Load WordPress
// d d
( __ __ ) p p p

// Parse what to query, and query it.
// Parse what to query and query it
wp();

// Load the theme.
// Load the theme

Before we get to the theme, we have
your posts.
Are we clear so far?

Then why do we do this?
Then why do we do this?
query_posts( 'author=5' );
(' h ')
g _
get_header( );
()

while( have_posts( ) ) :
while( have posts( ) ) :
the_post( );
endwhile;

get_footer( );

That s running 2 queries!
That’s running 2* queries!
One, the query WordPress
thought we wanted.
thought we wanted.

Two, this new one you’re
actually going to use.
actually going to use

* Actually, WP_Query doesn't run just one
query. It usually runs four.
query. It usually runs four.

1. Get me my posts: SELECT
_ _ _
SQL_CALC_FOUND_ROWS …
FROM wp_posts LIMIT 0, 10
2. How many posts exist?
2 How many posts exist?
SELECT FOUND_ROWS()
3. Pull down all metadata for these posts.
4. Pull down all terms for these posts.
4 Pull down all terms for these posts

Instead of query_posts()?
Instead of query posts()?
We can use this:

// In WP::parse_request()

$this >query_vars = apply_ﬁlters( request
$this‐>query vars = apply ﬁlters( 'request',
$this‐>query_vars );

We can modify query variables in mid
air:
function brady_filter_out_author( $qvs )
{
if( ! Isset( $qvs[‘author’] ) )
$qvs[‘author’] = ‘‐5’;

return $qvs;
}

Powerful, but lacks context.
Powerful but lacks context
Problems:

1. Conditional tags don’t work yet.

2. Only works on the main query.
2 Only works on the main query

3. WP_Query is way cooler.

Introducing pre_get_posts
Introducing pre get posts
class WP_Query
l WP Q
{
. . .
function &get_posts()
{
{
$this‐>parse_query();
// OMG! Conditional tags are available!!
do_action_ref_array( 'pre_get_posts', array( &$this ) );
}
. . .
}

Lets kill off query_posts()!
Lets kill off query posts()!
function brady_alter_home( $query )
{
if ( $query‐>is_home( ) )
$query‐>set( 'author', '‐5' );
}
add_action( 'pre_get_posts',
‘brady_alter_home' );

Still with us?
Still with us?
Good ‘cause here’s where things get hairy.

‘request’ fires for the main query only.
‘ ’ fi f h i l

‘pre_get_posts’ fires for every post query:

• get_posts()
• new WP_Query()
• That random recent posts widget.
That random recent posts widget
• Everything.

What if I just want it on the
main query?

$wp_the_query makes a
triumphant return.

Main query only!
Main query only!
function brady_alter_home( $query )
f i b d l h ($ )
{
if ( $query‐>is_home( ) &&
$wp_the_query === $query )
$wp the query === $query )
$query‐>set( 'author', '‐5' );
}
add_action( pre_get_posts
add action( 'pre get posts',
‘brady_alter_home' );

Hmm. How does this work?
Hmm How does this work?
$wp_the_query should never be modiﬁed. It
q y
holds the main query, forever.

$wp_query k
$ keeps a live reference to
li f
$wp_the_query, unless you use query_posts().

query_posts( 'author=‐5' );
while ( have_posts( ) ) :
while ( have posts( ) ) :
the_post( );
endwhile;
wp_reset_query( );
wp reset query( );

class WP_Query
l WP Q
{
. . .
function &query_posts( $query )
{
// Break the reference to $wp_the_query
// Break the reference to $wp the query
unset( $wp_query );
$wp_query =& new WP_Query( $query );
...
}
...
}

class WP_Query
class WP Query
{
. . .
function wp_reset_query( )
f ()
{
// Restore the reference to $wp_the_query
unset( $wp_query );
$wp_query =& $wp_the_query;
//
// Reset the globals, too.
g ,
wp_reset_postdata( );
. . .
}
....
}

Calling the_post( )? wp_reset_query( ) will reset
$wp_query and and the globals.
p_q y g

Calling $my_query‐>the_post( )?
C lli $ h ( )?
wp_reset_postdata( ) will reset the globals.

Since WordPress 3.3!
Since WordPress 3 3!
Rather than:
$wp_the_query
$wp the query === $other_query_object
$other query object

You‘re able to call:
$other_query_object >is_main_query( )
$other query object‐>is main query( )

Some Lessons
Some Lessons
Every WP_Query object has methods that mimic
g g
the global conditional tags.

The global conditional tags apply to $wp_query,
Th l b l di i l l $
the main or current query.

$wp_query i l
$ is always the main query, unless you
th i l
use query_posts( ). Restore it with
wp_reset_query( ).

And finally
And finally
request is a nice hook. pre_get_posts is more
p
powerful and ﬂexible. Just use it properly.
p p y

Always check if you're modifying the main query
Al h k if ' dif i h i
using $query‐>is_main_query( )

$query === $wp_the_query b f
$ $ th before 3.3
33

Thank you! Any questions?
Thank you! Any questions?
Further in‐depth discussion on query_posts():
• @l3rady on Twitter.
@l3rady on Twitter.
• Down the pub after presentations.

WordPress London 16 May 2012 - You don’t know query

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