/** * 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 * @access protected * @var array */ protected $pending_objects; /** * Settings for supported object types. * * @since 4.5.0 * @access protected * @var array */ protected $settings = array(); /** * Constructor. * * @since 4.5.0 * @access public */ 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 * @access public * * @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 bool|WP_Error True on success, 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 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 * @access public * * @param string $object_type Object type. Accepts 'comment' or 'term'. * @return bool|WP_Error True on success, 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 * @access public * * @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; } }