Prime users cache in WP_Query and post REST API controller.

For a call to `WP_Query` or a post REST API request that contains posts from multiple authors, call the `cache_users` function, to ensure that all user data for post authors is primed in 
a single database query. This results in far fewer database queries on multiple author sites. 

Props spacedmonkey, timothyblynjacobs, peterwilsoncc.
Fixes #55716.


git-svn-id: https://develop.svn.wordpress.org/trunk@53482 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -3434,6 +3434,9 @@ class WP_Query {
 	 */
 	public function the_post() {
 		global $post;
+		if ( ! $this->in_the_loop ) {
+			update_post_author_caches( $this->posts );
+		}
 		$this->in_the_loop = true;
 
 		if ( -1 == $this->current_post ) { // Loop has just started.

src/wp-includes/pluggable.php

@@ -132,6 +132,8 @@ if ( ! function_exists( 'cache_users' ) ) :
 	function cache_users( $user_ids ) {
 		global $wpdb;
 
+		update_meta_cache( 'user', $user_ids );
+
 		$clean = _get_non_cached_ids( $user_ids, 'users' );
 
 		if ( empty( $clean ) ) {
@@ -141,13 +143,9 @@ if ( ! function_exists( 'cache_users' ) ) :
 		$list = implode( ',', $clean );
 
 		$users = $wpdb->get_results( "SELECT * FROM $wpdb->users WHERE ID IN ($list)" );
-
-		$ids = array();
 		foreach ( $users as $user ) {
 			update_user_caches( $user );
-			$ids[] = $user->ID;
 		}
-		update_meta_cache( 'user', $ids );
 	}
 endif;
 

src/wp-includes/post.php

@@ -7474,6 +7474,20 @@ function update_post_caches( &$posts, $post_type = 'post', $update_term_cache =
 	}
 }
 
+/**
+ * Prime post author user caches.
+ *
+ * @since 6.1.0
+ *
+ * @param WP_Post[] $posts Array of Post objects
+ */
+function update_post_author_caches( $posts ) {
+	$author_ids = wp_list_pluck( $posts, 'post_author' );
+	$author_ids = array_map( 'absint', $author_ids );
+	$author_ids = array_unique( array_filter( $author_ids ) );
+	cache_users( $author_ids );
+}
+
 /**
  * Updates metadata cache for list of post IDs.
  *

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

@@ -369,6 +369,8 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 
 		$posts = array();
 
+		update_post_author_caches( $query_result );
+
 		foreach ( $query_result as $post ) {
 			if ( ! $this->check_read_permission( $post ) ) {
 				continue;

tests/phpunit/tests/query.php

@@ -620,6 +620,39 @@ class Tests_Query extends WP_UnitTestCase {
 		$this->assertSame( array( $p2 ), $q->posts );
 	}
 
+	/**
+	 * @ticket 55716
+	 */
+	public function test_prime_user_cache() {
+		$action = new MockAction();
+		add_filter( 'update_user_metadata_cache', array( $action, 'filter' ), 10, 2 );
+		$user_ids = array();
+		$count    = 5;
+		for ( $i = 0; $i < $count; $i ++ ) {
+			$user_ids[ $i ] = self::factory()->user->create();
+			self::factory()->post->create(
+				array(
+					'post_type'   => 'post',
+					'post_author' => $user_ids[ $i ],
+				)
+			);
+		}
+
+		$q = new WP_Query(
+			array(
+				'post_type'      => 'post',
+				'posts_per_page' => $count,
+			)
+		);
+		while ( $q->have_posts() ) {
+			$q->the_post();
+		}
+
+		$args      = $action->get_args();
+		$last_args = end( $args );
+		$this->assertSameSets( $user_ids, $last_args[1], 'Ensure that user ids are primed' );
+	}
+
 	/**
 	 * @ticket 35601
 	 */