Lazy load post meta

src/wp-admin/includes/dashboard.php

@@ -976,14 +976,15 @@ function wp_dashboard_site_activity() {
  */
 function wp_dashboard_recent_posts( $args ) {
 	$query_args = array(
-		'post_type'      => 'post',
-		'post_status'    => $args['status'],
-		'orderby'        => 'date',
-		'order'          => $args['order'],
-		'posts_per_page' => (int) $args['max'],
-		'no_found_rows'  => true,
-		'cache_results'  => true,
-		'perm'           => ( 'future' === $args['status'] ) ? 'editable' : 'readable',
+		'post_type'           => 'post',
+		'post_status'         => $args['status'],
+		'orderby'             => 'date',
+		'order'               => $args['order'],
+		'posts_per_page'      => (int) $args['max'],
+		'no_found_rows'       => true,
+		'cache_results'       => true,
+		'lazy_load_post_meta' => true,
+		'perm'                => ( 'future' === $args['status'] ) ? 'editable' : 'readable',
 	);
 
 	/**

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

@@ -61,6 +61,10 @@ public function __construct() {
 				'filter'   => 'get_comment_metadata',
 				'callback' => array( $this, 'lazyload_meta_callback' ),
 			),
+			'post'    => array(
+				'filter'   => 'get_post_metadata',
+				'callback' => array( $this, 'lazyload_meta_callback' ),
+			),
 			'blog'    => array(
 				'filter'   => 'get_blog_metadata',
 				'callback' => array( $this, 'lazyload_meta_callback' ),
@@ -187,6 +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

@@ -660,6 +660,7 @@ public function fill_query_vars( $query_vars ) {
 	 * @since 5.3.0 Introduced the `$meta_type_key` parameter.
 	 * @since 6.1.0 Introduced the `$update_menu_item_cache` parameter.
 	 * @since 6.2.0 Introduced the `$search_columns` parameter.
+	 * @since 6.8.0 Introduced the `$lazy_load_post_meta` parameter.
 	 *
 	 * @param string|array $query {
 	 *     Optional. Array or string of Query parameters.
@@ -796,6 +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. 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             $year                   The four-digit year. Default empty. Accepts any four-digit year.
 	 * }
@@ -1291,7 +1294,7 @@ public function parse_tax_query( &$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'            => $q['category__not_in'],
 				'operator'         => 'NOT IN',
@@ -1360,7 +1363,7 @@ public function parse_tax_query( &$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',
@@ -1996,6 +1999,15 @@ 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;
+		}
+
 		if ( ! isset( $q['post_type'] ) ) {
 			if ( $this->is_search ) {
 				$q['post_type'] = 'any';
@@ -3295,6 +3307,10 @@ public function get_posts() {
 			$this->post_count = count( $this->posts );
 			$this->set_found_posts( $q, $limits );
 
+			if ( $q['lazy_load_post_meta'] ) {
+				wp_lazyload_post_meta( $this->posts );
+			}
+
 			if ( $q['cache_results'] && $id_query_is_cacheable ) {
 				$cache_value = array(
 					'posts'         => $this->posts,
@@ -3333,6 +3349,10 @@ public function get_posts() {
 			// Prime post parent caches, so that on second run, there is not another database query.
 			wp_cache_add_multiple( $post_parents_cache, 'posts' );
 
+			if ( $q['lazy_load_post_meta'] ) {
+				wp_lazyload_post_meta( $post_ids );
+			}
+
 			if ( $q['cache_results'] && $id_query_is_cacheable ) {
 				$cache_value = array(
 					'posts'         => $post_ids,
@@ -3587,6 +3607,7 @@ public function get_posts() {
 						'update_post_meta_cache' => $q['update_post_meta_cache'],
 						'update_post_term_cache' => $q['update_post_term_cache'],
 						'lazy_load_term_meta'    => $q['lazy_load_term_meta'],
+						'lazy_load_post_meta'    => $q['lazy_load_post_meta'],
 					)
 				);
 
@@ -3644,6 +3665,11 @@ public function get_posts() {
 			wp_queue_posts_for_term_meta_lazyload( $this->posts );
 		}
 
+		if ( $q['lazy_load_post_meta'] ) {
+			$post_ids = wp_list_pluck( $this->posts, 'ID' );
+			wp_lazyload_post_meta( $post_ids );
+		}
+
 		return $this->posts;
 	}
 
@@ -3744,6 +3770,9 @@ public function the_post() {
 			$post_ids = array_filter( $post_ids );
 			if ( $post_ids ) {
 				_prime_post_caches( $post_ids, $this->query_vars['update_post_term_cache'], $this->query_vars['update_post_meta_cache'] );
+				if ( $this->query_vars['lazy_load_post_meta'] ) {
+					wp_lazyload_post_meta( $post_ids );
+				}
 			}
 			$post_objects = array_map( 'get_post', $this->posts );
 			update_post_author_caches( $post_objects );
@@ -4935,6 +4964,7 @@ protected function generate_cache_key( array $args, $sql ) {
 			$args['cache_results'],
 			$args['fields'],
 			$args['lazy_load_term_meta'],
+			$args['lazy_load_post_meta'],
 			$args['update_post_meta_cache'],
 			$args['update_post_term_cache'],
 			$args['update_menu_item_cache'],

src/wp-includes/nav-menu.php

@@ -807,7 +807,8 @@ function update_menu_item_cache( $menu_items ) {
 	}
 
 	if ( ! empty( $post_ids ) ) {
-		_prime_post_caches( $post_ids, false );
+		_prime_post_caches( $post_ids, false, false );
+		wp_lazyload_post_meta( $post_ids );
 	}
 
 	if ( ! empty( $term_ids ) ) {

src/wp-includes/post.php

@@ -2665,6 +2665,21 @@ function get_post_meta( $post_id, $key = '', $single = false ) {
 	return get_metadata( 'post', $post_id, $key, $single );
 }
 
+/**
+ * Queue post meta for lazy-loading.
+ *
+ * @since 6.8.0
+ *
+ * @param array $post_ids List of post IDs.
+ */
+function wp_lazyload_post_meta( array $post_ids ) {
+	if ( empty( $post_ids ) ) {
+		return;
+	}
+	$lazyloader = wp_metadata_lazyloader();
+	$lazyloader->queue_objects( 'post', $post_ids );
+}
+
 /**
  * Updates a post meta field based on the given post ID.
  *
@@ -7763,7 +7778,8 @@ function update_post_parent_caches( $posts ) {
 	$parent_ids = array_unique( array_filter( $parent_ids ) );
 
 	if ( ! empty( $parent_ids ) ) {
-		_prime_post_caches( $parent_ids, false );
+		_prime_post_caches( $parent_ids, false, false );
+		wp_lazyload_post_meta( $parent_ids );
 	}
 }
 

src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -411,6 +411,9 @@ static function ( $format ) {
 		// Force the post_type argument, since it's not a user input variable.
 		$args['post_type'] = $this->post_type;
 
+		// Lazy load post meta.
+		$args['lazy_load_post_meta'] = true;
+
 		/**
 		 * Filters WP_Query arguments when querying posts via the REST API.
 		 *

src/wp-includes/revision.php

@@ -670,9 +670,10 @@ function wp_get_post_revisions( $post = 0, $args = null ) {
 	$args = array_merge(
 		$args,
 		array(
-			'post_parent' => $post->ID,
-			'post_type'   => 'revision',
-			'post_status' => 'inherit',
+			'post_parent'         => $post->ID,
+			'post_type'           => 'revision',
+			'post_status'         => 'inherit',
+			'lazy_load_post_meta' => true,
 		)
 	);
 

tests/phpunit/includes/abstract-testcase.php

@@ -287,6 +287,7 @@ protected function reset_lazyload_queue() {
 		$lazyloader = wp_metadata_lazyloader();
 		$lazyloader->reset_queue( 'term' );
 		$lazyloader->reset_queue( 'comment' );
+		$lazyloader->reset_queue( 'post' );
 		$lazyloader->reset_queue( 'blog' );
 	}
 

tests/phpunit/tests/post/nav-menu.php

@@ -267,13 +267,13 @@ public function test_update_menu_item_cache_primes_posts() {
 
 		wp_cache_delete( $post_id, 'posts' );
 		$action = new MockAction();
-		add_filter( 'update_post_metadata_cache', array( $action, 'filter' ), 10, 2 );
+		add_action( 'metadata_lazyloader_queued_objects', array( $action, 'action' ) );
 
 		update_menu_item_cache( $query_result );
 
 		$args = $action->get_args();
 		$last = end( $args );
-		$this->assertSameSets( array( $post_id ), $last[1], '_prime_post_caches() was not executed.' );
+		$this->assertSameSets( array( $post_id ), $last[0], 'wp_lazyload_post_meta() was not executed.' );
 	}
 
 	/**
@@ -336,17 +336,20 @@ public function test_wp_get_nav_menu_items_cache_primes_posts() {
 		wp_cache_delete_multiple( $post_ids, 'posts' );
 		wp_cache_delete_multiple( $post_ids, 'post_meta' );
 
-		$action = new MockAction();
-		add_filter( 'update_post_metadata_cache', array( $action, 'filter' ), 10, 2 );
+		$action1 = new MockAction();
+		$action2 = new MockAction();
+		add_filter( 'update_post_metadata_cache', array( $action1, 'filter' ), 10, 2 );
+		add_action( 'metadata_lazyloader_queued_objects', array( $action2, 'action' ) );
 
 		$start_num_queries = get_num_queries();
 		wp_get_nav_menu_items( $this->menu_id, array( 'nopaging' => false ) );
 		$queries_made = get_num_queries() - $start_num_queries;
-		$this->assertSame( 7, $queries_made, 'Only does 7 database queries when running wp_get_nav_menu_items.' );
+		$this->assertSame( 6, $queries_made, 'Only does 6 database queries when running wp_get_nav_menu_items.' );
 
-		$args = $action->get_args();
-		$this->assertSameSets( $menu_nav_ids, $args[0][1], '_prime_post_caches() was not executed.' );
-		$this->assertSameSets( $post_ids, $args[2][1], '_prime_post_caches() was not executed.' );
+		$args1 = $action1->get_args();
+		$args2 = $action2->get_args();
+		$this->assertSameSets( $menu_nav_ids, $args1[0][1], '_prime_post_caches() was not executed.' );
+		$this->assertSameSets( $post_ids, $args2[0][0], 'lazy_load_post_meta() was not executed.' );
 	}
 
 	/**

tests/phpunit/tests/query/cacheResults.php

@@ -720,6 +720,10 @@ public function data_query_cache_duplicate() {
 					'update_menu_item_cache' => false,
 				),
 			),
+			'lazy load post meta'                          => array(
+				'query_vars1' => array( 'lazy_load_post_meta' => true ),
+				'query_vars2' => array( 'lazy_load_post_meta' => false ),
+			),
 		);
 	}
 

tests/phpunit/tests/query/lazyLoadPostMeta.php

@@ -0,0 +1,102 @@
+<?php
+
+/**
+ * @group query
+ * @group meta
+ */
+class Tests_Lazy_Load_Post_Meta extends WP_UnitTestCase {
+	/**
+	 * Post IDs.
+	 *
+	 * @var int[]
+	 */
+	private static $post_ids = array();
+
+	public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
+		// Register CPT for use with shared fixtures.
+		register_post_type( 'wptests_pt' );
+
+		self::$post_ids = $factory->post->create_many( 5, array( 'post_type' => 'wptests_pt' ) );
+		foreach ( self::$post_ids as $post_id ) {
+			update_post_meta( $post_id, 'foo', 'bar' );
+		}
+	}
+
+	/**
+	 * @dataProvider data_lazy_load_post_meta
+	 * @ticket 57496
+	 */
+	public function test_lazy_load_post_meta( $query_args ) {
+		wp_cache_delete_multiple( self::$post_ids, 'posts' );
+		wp_cache_delete_multiple( self::$post_ids, 'post_meta' );
+		$action1 = new MockAction();
+		$action2 = new MockAction();
+		add_filter( 'update_post_metadata_cache', array( $action1, 'filter' ), 10, 2 );
+		add_action( 'metadata_lazyloader_queued_objects', array( $action2, 'action' ) );
+
+		new WP_Query( $query_args );
+
+		$args1 = $action1->get_args();
+		$args2 = $action2->get_args();
+		$last  = end( $args2 );
+		$this->assertSameSets( self::$post_ids, $last[0], 'wp_lazyload_post_meta() was not executed.' );
+		$this->assertSameSets( array(), $args1, 'update_meta_cache() was executed.' );
+		$num_queries = get_num_queries();
+		get_post_meta( self::$post_ids[0], 'foo', true );
+		$this->assertSame( $num_queries + 1, get_num_queries(), 'wp_lazyload_post_meta() was not executed.' );
+		$args1 = $action1->get_args();
+		$last  = end( $args1 );
+		$this->assertSameSets( self::$post_ids, $last[1], 'update_meta_cache() was not executed.' );
+	}
+
+	/**
+	 * Provides test data for lazy loading post metadata.
+	 *
+	 * @return array
+	 */
+	public function data_lazy_load_post_meta() {
+		return array(
+			'lazy load post meta'                       => array(
+				array(
+					'post_type'           => 'wptests_pt',
+					'lazy_load_post_meta' => true,
+				),
+			),
+			'lazy load post meta fields id'             => array(
+				array(
+					'post_type'           => 'wptests_pt',
+					'fields'              => 'ids',
+					'lazy_load_post_meta' => true,
+				),
+			),
+			'lazy load post meta fields id=>parent'     => array(
+				array(
+					'post_type'           => 'wptests_pt',
+					'fields'              => 'id=>parent',
+					'lazy_load_post_meta' => true,
+				),
+			),
+			'lazy load post meta - update_post_meta_cache true' => array(
+				array(
+					'post_type'              => 'wptests_pt',
+					'update_post_meta_cache' => true,
+					'lazy_load_post_meta'    => true,
+				),
+			),
+			'lazy load post meta - update_post_meta_cache false' => array(
+				array(
+					'post_type'              => 'wptests_pt',
+					'update_post_meta_cache' => false,
+					'lazy_load_post_meta'    => true,
+				),
+			),
+			'lazy load post meta - cache_results false' => array(
+				array(
+					'post_type'           => 'wptests_pt',
+					'cache_results'       => false,
+					'lazy_load_post_meta' => true,
+				),
+			),
+		);
+	}
+}

tests/phpunit/tests/query/stickies.php

@@ -123,6 +123,7 @@ public function test_stickies_should_obey_parameters_from_the_main_query() {
 		$this->assertSame( $query_vars['update_post_meta_cache'], $sticky_query_vars['update_post_meta_cache'] );
 		$this->assertSame( $query_vars['update_post_term_cache'], $sticky_query_vars['update_post_term_cache'] );
 		$this->assertSame( $query_vars['lazy_load_term_meta'], $sticky_query_vars['lazy_load_term_meta'] );
+		$this->assertSame( $query_vars['lazy_load_post_meta'], $sticky_query_vars['lazy_load_post_meta'] );
 		$this->assertTrue( $sticky_query_vars['ignore_sticky_posts'] );
 		$this->assertTrue( $sticky_query_vars['no_found_rows'] );
 	}