Allow term meta lazy-loading to be selectively disabled in WP_Query.

The process of lazy-loading can be resource intensive for object that have
terms in large numbers of taxonomies and are running a persistent object cache.
This new parameter allows the feature to be disabled in these cases.

Props DBrumbaugh10Up.
See #36953.

git-svn-id: https://develop.svn.wordpress.org/trunk@37589 602fd350-edb4-49c9-b593-d223f7449a82

Author: boonebgorges

src/wp-includes/query.php

@@ -1468,7 +1468,7 @@ public function fill_query_vars($array) {
 	 * @since 4.5.0 Removed the `$comments_popup` parameter.
 	 *              Introduced the `$comment_status` and `$ping_status` parameters.
 	 *              Introduced `RAND(x)` syntax for `$orderby`, which allows an integer seed value to random sorts.
-	 * @since 4.6.0 Added 'post_name__in' support for `$orderby`.
+	 * @since 4.6.0 Added 'post_name__in' support for `$orderby`. Introduced `$lazy_load_term_meta`.
 	 * @access public
 	 *
 	 * @param string|array $query {
@@ -1567,6 +1567,10 @@ public function fill_query_vars($array) {
 	 *     @type string       $title                   Post title.
 	 *     @type bool         $update_post_meta_cache  Whether to update the post meta cache. Default true.
 	 *     @type bool         $update_post_term_cache  Whether to update the post term cache. Default true.
+	 *     @type bool         $lazy_load_term_meta     Whether to lazy-load term meta. Setting to false will
+	 *                                                 disable cache priming for term meta, so that each
+	 *                                                 get_term_meta() call will hit the database.
+	 *                                                 Defaults to the value of `$update_post_term_cache`.
 	 *     @type int          $w                       The week number of the year. Default empty. Accepts numbers 0-53.
 	 *     @type int          $year                    The four-digit year. Default empty. Accepts any four-digit year.
 	 * }
@@ -2545,6 +2549,10 @@ public function get_posts() {
 		if ( !isset($q['update_post_term_cache']) )
 			$q['update_post_term_cache'] = true;
 
+		if ( ! isset( $q['lazy_load_term_meta'] ) ) {
+			$q['lazy_load_term_meta'] = $q['update_post_term_cache'];
+		}
+
 		if ( !isset($q['update_post_meta_cache']) )
 			$q['update_post_meta_cache'] = true;
 
@@ -3782,7 +3790,7 @@ public function get_posts() {
 			$this->posts = array();
 		}
 
-		if ( $q['update_post_term_cache'] ) {
+		if ( $q['lazy_load_term_meta'] ) {
 			wp_queue_posts_for_term_meta_lazyload( $this->posts );
 		}
 

tests/phpunit/tests/term/meta.php

@@ -150,6 +150,61 @@ public function test_term_meta_should_be_lazy_loaded_for_all_terms_in_wp_query_l
 		}
 	}
 
+	/**
+	 * @ticket 36593
+	 */
+	public function test_lazy_load_term_meta_should_fall_back_on_update_post_term_cache() {
+		$q = new WP_Query( array(
+			'update_post_term_cache' => true,
+		) );
+
+		$this->assertTrue( $q->get( 'lazy_load_term_meta' ) );
+
+		$q = new WP_Query( array(
+			'update_post_term_cache' => false,
+		) );
+
+		$this->assertFalse( $q->get( 'lazy_load_term_meta' ) );
+	}
+
+	/**
+	 * @ticket 36593
+	 */
+	public function test_lazy_load_term_meta_false() {
+		global $wpdb;
+
+		$p = self::factory()->post->create( array( 'post_status' => 'publish' ) );
+
+		register_taxonomy( 'wptests_tax', 'post' );
+		$terms = self::factory()->term->create_many( 3, array( 'taxonomy' => 'wptests_tax' ) );
+		wp_set_object_terms( $p, $terms, 'wptests_tax' );
+		foreach ( $terms as $t ) {
+			add_term_meta( $t, 'foo', 'bar' );
+		}
+
+		$q = new WP_Query( array(
+			'cache_results' => true,
+			'update_post_term_cache' => true,
+			'lazy_load_term_meta' => false,
+		) );
+
+		if ( $q->have_posts() ) {
+			while ( $q->have_posts() ) {
+				$q->the_post();
+
+				// Requests will hit the database.
+				$num_queries = $wpdb->num_queries;
+				$this->assertSame( 'bar', get_term_meta( $terms[0], 'foo', true ) );
+				$num_queries++;
+				$this->assertSame( $num_queries, $wpdb->num_queries );
+
+				$this->assertSame( 'bar', get_term_meta( $terms[1], 'foo', true ) );
+				$num_queries++;
+				$this->assertSame( $num_queries, $wpdb->num_queries );
+			}
+		}
+	}
+
 	public function test_adding_term_meta_should_bust_get_terms_cache() {
 		$terms = self::factory()->term->create_many( 2, array( 'taxonomy' => 'wptests_tax' ) );