Lazy load post meta

src/wp-includes/class-wp-metadata-lazyloader.php

@@ -63,7 +63,7 @@ public function __construct() {
 			),
 			'post'    => array(
 				'filter'   => 'get_post_metadata',
-				'callback' => array( $this, 'lazyload_post_meta' ),
+				'callback' => array( $this, 'lazyload_meta_callback' ),
 			),
 			'blog'    => array(
 				'filter'   => 'get_blog_metadata',
@@ -167,41 +167,6 @@ public function lazyload_comment_meta( $check ) {
 		return $this->lazyload_meta_callback( $check, 0, '', false, 'comment' );
 	}
 
-	/**
-	 * Lazy-loads post meta for queued posts.
-	 *
-	 * 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 6.8.0
-	 *
-	 * @param mixed  $check     The `$check` param passed from the 'get_*_metadata' hook.
-	 * @param int    $object_id ID of the object metadata is for.
-	 * @param string $meta_key  Unused.
-	 * @param bool   $single    Unused.
-	 * @param string $meta_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
-	 *                          or any other object type with an associated meta table.
-	 * @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_post_meta( $check, $object_id, $meta_key, $single, $meta_type ) {
-		if ( empty( $this->pending_objects[ $meta_type ] ) ) {
-			return $check;
-		}
-
-		$object_ids = array_keys( $this->pending_objects[ $meta_type ] );
-		if ( $object_id && ! in_array( $object_id, $object_ids, true ) ) {
-			return $check;
-		}
-
-		update_meta_cache( $meta_type, $object_ids );
-
-		// No need to run again for this set of objects.
-		$this->reset_queue( $meta_type );
-
-		return $check;
-	}
-
 	/**
 	 * Lazy-loads meta for queued objects.
 	 *
@@ -226,6 +191,10 @@ public function lazyload_meta_callback( $check, $object_id, $meta_key, $single,
 
 		$object_ids = array_keys( $this->pending_objects[ $meta_type ] );
 		if ( $object_id && ! in_array( $object_id, $object_ids, true ) ) {
+			// Only load in the post meta value is in the queue.
+			if ( 'post' === $meta_type ) {
+				return $check;
+			}
 			$object_ids[] = $object_id;
 		}
 

src/wp-includes/class-wp-query.php

@@ -797,9 +797,8 @@ public function fill_query_vars( $query_vars ) {
 	 *                                                   disable cache priming for term meta, so that each
 	 *                                                   get_term_meta() call will hit the database.
 	 *                                                   Defaults to the value of `$update_post_term_cache`.
-	 *     @type bool            $lazy_load_post_meta    Whether to lazy-load post meta. Setting to false will
-	 *                                                   disable cache priming for post meta, so that each
-	 *                                                   get_post_meta() call will hit the database.
+	 *     @type bool            $lazy_load_post_meta    Whether to lazy-load post meta. If set to false, post meta priming will
+	 *                                                   fallback to the default behavior of priming post meta.
 	 *     @type int             $w                      The week number of the year. Default empty. Accepts numbers 0-53.
 	 *     @type int             $year                   The four-digit year. Default empty. Accepts any four-digit year.
 	 * }
@@ -1295,7 +1294,7 @@ public function parse_tax_query( &$q ) {
 		if ( ! empty( $q['category__not_in'] ) ) {
 			$q['category__not_in'] = array_map( 'absint', array_unique( (array) $q['category__not_in'] ) );
 			sort( $q['category__not_in'] );
-			$tax_query[]           = array(
+			$tax_query[] = array(
 				'taxonomy'         => 'category',
 				'terms'            => $q['category__not_in'],
 				'operator'         => 'NOT IN',
@@ -1364,7 +1363,7 @@ public function parse_tax_query( &$q ) {
 		if ( ! empty( $q['tag__not_in'] ) ) {
 			$q['tag__not_in'] = array_map( 'absint', array_unique( (array) $q['tag__not_in'] ) );
 			sort( $q['tag__not_in'] );
-			$tax_query[]      = array(
+			$tax_query[] = array(
 				'taxonomy' => 'post_tag',
 				'terms'    => $q['tag__not_in'],
 				'operator' => 'NOT IN',
@@ -2000,9 +1999,12 @@ public function get_posts() {
 			$q['update_post_meta_cache'] = true;
 		}
 
+		// Default lazy loading post meta to false, as this `update_post_meta_cache` defaults to true.
+		// To correctly use the lazy_load_post_meta parameter, you must set update_post_meta_cache to false first.
 		if ( ! isset( $q['lazy_load_post_meta'] ) ) {
 			$q['lazy_load_post_meta'] = false;
 		} elseif ( $q['lazy_load_post_meta'] ) {
+			// Lazy loading post meta only works if post meta caches are not primed.
 			$q['update_post_meta_cache'] = false;
 		}
 

tests/phpunit/tests/query/cacheResults.php

@@ -720,7 +720,7 @@ public function data_query_cache_duplicate() {
 					'update_menu_item_cache' => false,
 				),
 			),
-			'lazy load post meta'       => array(
+			'lazy load post meta'                          => array(
 				'query_vars1' => array( 'lazy_load_post_meta' => true ),
 				'query_vars2' => array( 'lazy_load_post_meta' => false ),
 			),