spacedmonkey · Feb 26, 2025 · Sep 19, 2025 · Sep 19, 2025 · Sep 29, 2025 · Sep 29, 2025
diff --git a/src/wp-includes/class-wp-metadata-lazyloader.php b/src/wp-includes/class-wp-metadata-lazyloader.php
@@ -65,6 +65,10 @@ public function __construct() {
 				'filter'   => 'get_blog_metadata',
 				'callback' => array( $this, 'lazyload_meta_callback' ),
 			),
+			'user'    => array(
+				'filter'   => 'get_user_metadata',
+				'callback' => array( $this, 'lazyload_meta_callback' ),
+			),
 		);
 	}
 

diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
@@ -131,7 +131,8 @@ function get_user_by( $field, $value ) {
 	function cache_users( $user_ids ) {
 		global $wpdb;
 
-		update_meta_cache( 'user', $user_ids );
+		$user_ids = array_unique( array_map( 'intval', $user_ids ), SORT_NUMERIC );
+		wp_lazyload_user_meta( $user_ids );
 
 		$clean = _get_non_cached_ids( $user_ids, 'users' );
 

diff --git a/src/wp-includes/user.php b/src/wp-includes/user.php
@@ -1357,6 +1357,21 @@ function update_user_meta( $user_id, $meta_key, $meta_value, $prev_value = '' )
 	return update_metadata( 'user', $user_id, $meta_key, $meta_value, $prev_value );
 }
 
+/**
+ * Queue user meta for lazy-loading.
+ *
+ * @since 6.9.0
+ *
+ * @param int[] $user_ids List of user IDs.
+ */
+function wp_lazyload_user_meta( array $user_ids ) {
+	if ( empty( $user_ids ) ) {
+		return;
+	}
+	$lazyloader = wp_metadata_lazyloader();
+	$lazyloader->queue_objects( 'user', $user_ids );
+}
+
 /**
  * Counts number of users who have each of the user roles.
  *

diff --git a/tests/phpunit/includes/abstract-testcase.php b/tests/phpunit/includes/abstract-testcase.php
@@ -368,6 +368,7 @@ protected function reset_lazyload_queue() {
 		$lazyloader->reset_queue( 'term' );
 		$lazyloader->reset_queue( 'comment' );
 		$lazyloader->reset_queue( 'blog' );
+		$lazyloader->reset_queue( 'user' );
 	}
 
 	/**

diff --git a/tests/phpunit/tests/post/updatePostAuthorCaches.php b/tests/phpunit/tests/post/updatePostAuthorCaches.php
@@ -67,6 +67,28 @@ public function test_update_post_author_caches() {
 			$q->the_post();
 		}
 
+		$this->assertSame( 0, $action->get_call_count(), 'Ensure that user meta are not primed' );
+	}
+
+	/**
+	 * @ticket 63021
+	 */
+	public function test_update_post_author_caches_force_load_meta() {
+		$action = new MockAction();
+		add_filter( 'update_user_metadata_cache', array( $action, 'filter' ), 10, 2 );
+
+		$q = new WP_Query(
+			array(
+				'post_type'      => 'post',
+				'posts_per_page' => self::$post_author_count,
+			)
+		);
+
+		while ( $q->have_posts() ) {
+			$q->the_post();
+			get_the_author_meta(); // Force loading of author meta.
+		}
+
 		$args      = $action->get_args();
 		$last_args = end( $args );
 

diff --git a/tests/phpunit/tests/query/cacheResults.php b/tests/phpunit/tests/query/cacheResults.php
@@ -1981,11 +1981,10 @@ public function test_author_cache_warmed_by_the_loop( $fields ) {
 		$query_1->the_post();
 		$num_loop_queries = get_num_queries() - $start_loop_queries;
 		/*
-		 * Two expected queries:
-		 * 1: User meta data,
-		 * 2: User data.
+		 * One expected query:
+		 * 1: User data.
 		 */
-		$this->assertSame( 2, $num_loop_queries, 'Unexpected number of queries while initializing the loop.' );
+		$this->assertSame( 1, $num_loop_queries, 'Unexpected number of queries while initializing the loop.' );
 
 		$start_author_queries = get_num_queries();
 		get_user_by( 'ID', self::$author_id );

diff --git a/tests/phpunit/tests/query/thePost.php b/tests/phpunit/tests/query/thePost.php
@@ -265,10 +265,10 @@ public function test_the_loop_primes_the_author_cache( $fields, $expected_querie
 	 */
 	public function data_the_loop_fields() {
 		return array(
-			'all fields'                => array( 'all', 2 ),
-			'all fields (empty fields)' => array( '', 2 ),
-			'post IDs'                  => array( 'ids', 4 ),
-			'post ids and parent'       => array( 'id=>parent', 4 ),
+			'all fields'                => array( 'all', 1 ),
+			'all fields (empty fields)' => array( '', 1 ),
+			'post IDs'                  => array( 'ids', 3 ),
+			'post ids and parent'       => array( 'id=>parent', 3 ),
 		);
 	}
 

diff --git a/tests/phpunit/tests/user/lazyLoadMeta.php b/tests/phpunit/tests/user/lazyLoadMeta.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * @group user
+ * @covers ::wp_lazyload_user_meta
+ */
+class Tests_User_Lazy_Load_Meta extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 63021
+	 */
+	public function test_lazy_load_meta() {
+		$user_ids = self::factory()->user->create_many( 3 );
+		// Clear any existing cache.
+		wp_cache_delete_multiple( $user_ids, 'user_meta' );
+		wp_lazyload_user_meta( $user_ids );
+		$filter = new MockAction();
+		add_filter( 'update_user_metadata_cache', array( $filter, 'filter' ), 10, 2 );
+		get_user_meta( $user_ids[0] );
+
+		$args          = $filter->get_args();
+		$first         = reset( $args );
+		$load_user_ids = end( $first );
+		$this->assertSameSets( $user_ids, $load_user_ids, 'Ensure all user IDs are loaded in a single batch' );
+	}
+
+	/**
+	 * @ticket 63021
+	 */
+	public function test_lazy_load_meta_sets() {
+		$user_ids1 = self::factory()->user->create_many( 3 );
+		$user_ids2 = self::factory()->user->create_many( 3 );
+		$user_ids  = array_merge( $user_ids1, $user_ids2 );
+		// Clear any existing cache.
+		wp_cache_delete_multiple( $user_ids, 'user_meta' );
+		wp_lazyload_user_meta( $user_ids );
+		$filter = new MockAction();
+		add_filter( 'update_user_metadata_cache', array( $filter, 'filter' ), 10, 2 );
+		get_user_meta( $user_ids[0] );
+
+		$args          = $filter->get_args();
+		$first         = reset( $args );
+		$load_user_ids = end( $first );
+		$this->assertSameSets( $user_ids, $load_user_ids, 'Ensure all user IDs are loaded in a single batch' );
+	}
+
+	/**
+	 * @ticket 63021
+	 */
+	public function test_lazy_load_meta_not_in_queue() {
+		$user_ids1   = self::factory()->user->create_many( 3 );
+		$user_ids2   = self::factory()->user->create_many( 3 );
+		$user_ids    = array_merge( $user_ids1, $user_ids2 );
+		$new_user_id = self::factory()->user->create();
+		wp_lazyload_user_meta( $user_ids );
+		// Add a user not in the lazy load queue.
+		$user_ids[] = $new_user_id;
+		// Clear any existing cache including the new user not in the queue.
+		wp_cache_delete_multiple( $user_ids, 'user_meta' );
+
+		$filter = new MockAction();
+		add_filter( 'update_user_metadata_cache', array( $filter, 'filter' ), 10, 2 );
+		get_user_meta( $new_user_id );
+
+		$args          = $filter->get_args();
+		$first         = reset( $args );
+		$load_user_ids = end( $first );
+		$this->assertSameSets( $user_ids, $load_user_ids, 'Ensure all user IDs are loaded, including the one not in the queue' );
+	}
+}