<?php
/**
* Meta API: WP_Metadata_Lazyloader class
*
* @package WordPress
* @subpackage Meta
* @since 4.5.0
*/
/**
* Core class used for lazy-loading object metadata.
*
* When loading many objects of a given type, such as posts in a WP_Query loop, it often makes
* sense to prime various metadata caches at the beginning of the loop. This means fetching all
* relevant metadata with a single database query, a technique that has the potential to improve
* performance dramatically in some cases.
*
* In cases where the given metadata may not even be used in the loop, we can improve performance
* even more by only priming the metadata cache for affected items the first time a piece of metadata
* is requested - ie, by lazy-loading it. So, for example, comment meta may not be loaded into the
* cache in the comments section of a post until the first time get_comment_meta() is called in the
* context of the comment loop.
*
* WP uses the WP_Metadata_Lazyloader class to queue objects for metadata cache priming. The class
* then detects the relevant get_*_meta() function call, and queries the metadata of all queued objects.
*
* Do not access this class directly. Use the wp_metadata_lazyloader() function.
*
* @since 4.5.0
*/
class WP_Metadata_Lazyloader {
/**
* Pending objects queue.
*
* @since 4.5.0
* @var array
*/
protected $pending_objects;
/**
* Settings for supported object types.
*
* @since 4.5.0
* @var array
*/
protected $settings = array();
/**
* Constructor.
*
* @since 4.5.0
*/
public function __construct() {
$this->settings = array(
'term' => array(
'filter' => 'get_term_metadata',
'callback' => array( $this, 'lazyload_term_meta' ),
),
'comment' => array(
'filter' => 'get_comment_metadata',
'callback' => array( $this, 'lazyload_comment_meta' ),
),
);
}
/**
* Adds objects to the metadata lazy-load queue.
*
* @since 4.5.0
*
* @param string $object_type Type of object whose meta is to be lazy-loaded. Accepts 'term' or 'comment'.
* @param array $object_ids Array of object IDs.
* @return void|WP_Error WP_Error on failure.
*/
public function queue_objects( $object_type, $object_ids ) {
if ( ! isset( $this->settings[ $object_type ] ) ) {
return new WP_Error( 'invalid_object_type', __( 'Invalid object type.' ) );
}
$type_settings = $this->settings[ $object_type ];
if ( ! isset( $this->pending_objects[ $object_type ] ) ) {
$this->pending_objects[ $object_type ] = array();
}
foreach ( $object_ids as $object_id ) {
// Keyed by ID for faster lookup.
if ( ! isset( $this->pending_objects[ $object_type ][ $object_id ] ) ) {
$this->pending_objects[ $object_type ][ $object_id ] = 1;
}
}
add_filter( $type_settings['filter'], $type_settings['callback'] );
/**
* Fires after objects are added to the metadata lazy-load queue.
*
* @since 4.5.0
*
* @param array $object_ids Array of object IDs.
* @param string $object_type Type of object being queued.
* @param WP_Metadata_Lazyloader $lazyloader The lazy-loader object.
*/
do_action( 'metadata_lazyloader_queued_objects', $object_ids, $object_type, $this );
}
/**
* Resets lazy-load queue for a given object type.
*
* @since 4.5.0
*
* @param string $object_type Object type. Accepts 'comment' or 'term'.
* @return void|WP_Error WP_Error on failure.
*/
public function reset_queue( $object_type ) {
if ( ! isset( $this->settings[ $object_type ] ) ) {
return new WP_Error( 'invalid_object_type', __( 'Invalid object type.' ) );
}
$type_settings = $this->settings[ $object_type ];
$this->pending_objects[ $object_type ] = array();
remove_filter( $type_settings['filter'], $type_settings['callback'] );
}
/**
* Lazy-loads term meta for queued terms.
*
* This method is public so that it can be used as a filter callback. As a rule, there
* is no need to invoke it directly.
*
* @since 4.5.0
*
* @param mixed $check The `$check` param passed from the 'get_term_metadata' hook.
* @return mixed In order not to short-circuit `get_metadata()`. Generally, this is `null`, but it could be
* another value if filtered by a plugin.
*/
public function lazyload_term_meta( $check ) {
if ( ! empty( $this->pending_objects['term'] ) ) {
update_termmeta_cache( array_keys( $this->pending_objects['term'] ) );
// No need to run again for this set of terms.
$this->reset_queue( 'term' );
}
return $check;
}
/**
* Lazy-loads comment meta for queued comments.
*
* This method is public so that it can be used as a filter callback. As a rule, there is no need to invoke it
* directly, from either inside or outside the `WP_Query` object.
*
* @since 4.5.0
*
* @param mixed $check The `$check` param passed from the {@see 'get_comment_metadata'} hook.
* @return mixed The original value of `$check`, so as not to short-circuit `get_comment_metadata()`.
*/
public function lazyload_comment_meta( $check ) {
if ( ! empty( $this->pending_objects['comment'] ) ) {
update_meta_cache( 'comment', array_keys( $this->pending_objects['comment'] ) );
// No need to run again for this set of comments.
$this->reset_queue( 'comment' );
}
return $check;
}
}