Query: Cache the result when get_pages() doesn't find anything in t…

…he database.

Props flixos90, soulseekah.
Fixes #43514.



git-svn-id: https://develop.svn.wordpress.org/trunk@44587 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post.php

@@ -5057,7 +5057,8 @@ function get_pages( $args = array() ) {
 	$last_changed = wp_cache_get_last_changed( 'posts' );
 
 	$cache_key = "get_pages:$key:$last_changed";
-	if ( $cache = wp_cache_get( $cache_key, 'posts' ) ) {
+	$cache     = wp_cache_get( $cache_key, 'posts' );
+	if ( false !== $cache ) {
 		// Convert to WP_Post instances.
 		$pages = array_map( 'get_post', $cache );
 		/** This filter is documented in wp-includes/post.php */
@@ -5218,6 +5219,8 @@ function get_pages( $args = array() ) {
 	$pages = $wpdb->get_results( $query );
 
 	if ( empty( $pages ) ) {
+		wp_cache_set( $cache_key, array(), 'posts' );
+
 		/** This filter is documented in wp-includes/post.php */
 		$pages = apply_filters( 'get_pages', array(), $r );
 		return $pages;

tests/phpunit/tests/post/getPages.php

@@ -700,4 +700,26 @@ function test_exclude_tree() {
 		$exclude6 = get_pages( array( 'exclude_tree' => array( $post_id1, $post_id3 ) ) );
 		$this->assertCount( 2, $exclude6 );
 	}
+
+	/**
+	 * @ticket 43514
+	 */
+	function test_get_pages_cache_empty() {
+		global $wpdb;
+
+		wp_cache_delete( 'last_changed', 'posts' );
+		$this->assertFalse( wp_cache_get( 'last_changed', 'posts' ) );
+
+		$num_queries = $wpdb->num_queries;
+
+		$pages = get_pages(); // Database gets queried
+
+		$this->assertEquals( $num_queries + 1, $wpdb->num_queries );
+
+		$num_queries = $wpdb->num_queries;
+
+		$pages = get_pages(); // Database should not get queried
+
+		$this->assertEquals( $num_queries, $wpdb->num_queries );
+	}
 }