Improve post field lazyloading for comments.

[34583] modified comment queries so that all post fields are no longer loaded
by default. Instead, they are loaded only when requested on individual comment
objects. This changeset improves that flow:

* `WP_Comment` magic methods `__isset()` and `__get()` should only load the post when a post field is being requested.
* The new `update_comment_post_cache` argument for `WP_Comment_Query` allows developers to specify that, when comments are queried, all of the posts matching those comments should be loaded into cache with a single DB hit. This parameter defaults to false, since typical comment queries are linked to a single post.

Fixes #27571.

git-svn-id: https://develop.svn.wordpress.org/trunk@34599 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -138,7 +138,7 @@ class WP_Comment_Query {
 	 * @since 4.2.0
 	 * @since 4.4.0 `$parent__in` and `$parent__not_in` were added.
 	 * @since 4.4.0 Order by `comment__in` was added. `$update_comment_meta_cache`, `$no_found_rows`,
-	 *              and `$hierarchical` were added.
+	 *              `$hierarchical`, and `$update_comment_post_cache` were added.
 	 * @access public
 	 *
 	 * @param string|array $query {
@@ -238,6 +238,8 @@ class WP_Comment_Query {
 	 *                                                   'flat', or false. Default: false.
 	 *     @type bool         $update_comment_meta_cache Whether to prime the metadata cache for found comments.
 	 *                                                   Default true.
+	 *     @type bool         $update_comment_post_cache Whether to prime the cache for comment posts.
+	 *                                                   Default false.
 	 * }
 	 */
 	public function __construct( $query = '' ) {
@@ -281,6 +283,7 @@ class WP_Comment_Query {
 			'date_query' => null, // See WP_Date_Query
 			'hierarchical' => false,
 			'update_comment_meta_cache' => true,
+			'update_comment_post_cache' => false,
 		);
 
 		if ( ! empty( $query ) ) {
@@ -414,6 +417,16 @@ class WP_Comment_Query {
 			}
 		}
 
+		// Prime comment post caches.
+		if ( $this->query_vars['update_comment_post_cache'] ) {
+			$comment_post_ids = array();
+			foreach ( $_comments as $_comment ) {
+				$comment_post_ids[] = $_comment->comment_post_ID;
+			}
+
+			_prime_post_caches( $comment_post_ids, false, false );
+		}
+
 		/**
 		 * Filter the comment query results.
 		 *

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

@@ -158,6 +158,15 @@ final class WP_Comment {
 	 */
 	protected $children;
 
+	/**
+	 * Post fields.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 * @var array
+	 */
+	protected $post_fields = array( 'post_author', 'post_date', 'post_date_gmt', 'post_content', 'post_title', 'post_excerpt', 'post_status', 'comment_status', 'ping_status', 'post_name', 'to_ping', 'pinged', 'post_modified', 'post_modified_gmt', 'post_content_filtered', 'post_parent', 'guid', 'menu_order', 'post_type', 'post_mime_type', 'comment_count' );
+
 	/**
 	 * Retrieves a WP_Comment instance.
 	 *
@@ -322,30 +331,27 @@ final class WP_Comment {
 	}
 
 	/**
-	 * Whether a comment has post from which to retrieve magic properties
+	 * Check whether a non-public property is set.
+	 *
+	 * If `$name` matches a post field, the comment post will be loaded and the post's value checked.
 	 *
 	 * @since 4.4.0
 	 * @access public
 	 *
-	 * @param string $name
+	 * @param string $name Property name.
 	 * @return bool
 	 */
 	public function __isset( $name ) {
-		if (
-			0 === (int) $this->comment_post_ID
-			|| property_exists( $this, $name )
-		) {
-			return;
-		}
-
-		$post = get_post( $this->comment_post_ID );
-		if ( $post ) {
+		if ( in_array( $name, $this->post_fields ) && 0 !== (int) $this->comment_post_ID ) {
+			$post = get_post( $this->comment_post_ID );
 			return property_exists( $post, $name );
 		}
 	}
 
 	/**
-	 * Magic getter for $post properties
+	 * Magic getter.
+	 *
+	 * If `$name` matches a post field, the comment post will be loaded and the post's value returned.
 	 *
 	 * @since 4.4.0
 	 * @access public
@@ -354,8 +360,8 @@ final class WP_Comment {
 	 * @return mixed
 	 */
 	public function __get( $name ) {
-		$post = get_post( $this->comment_post_ID );
-		if ( $post ) {
+		if ( in_array( $name, $this->post_fields ) ) {
+			$post = get_post( $this->comment_post_ID );
 			return $post->$name;
 		}
 	}

tests/phpunit/tests/comment.php

@@ -339,4 +339,23 @@ class Tests_Comment extends WP_UnitTestCase {
 		// Direct descendants of $c2.
 		$this->assertEquals( array( $c3 ), array_values( wp_list_pluck( $children[ $c2 ]->get_children(), 'comment_ID' ) ) );
 	}
+
+	/**
+	 * @group 27571
+	 */
+	public function test_post_properties_should_be_lazyloaded() {
+		$p = $this->factory->post->create();
+
+		$c = $this->factory->comment->create( array( 'comment_post_ID' => $p ) );
+
+		$post = get_post( $p );
+		$comment = get_comment( $c );
+
+		$post_fields = array( 'post_author', 'post_date', 'post_date_gmt', 'post_content', 'post_title', 'post_excerpt', 'post_status', 'comment_status', 'ping_status', 'post_name', 'to_ping', 'pinged', 'post_modified', 'post_modified_gmt', 'post_content_filtered', 'post_parent', 'guid', 'menu_order', 'post_type', 'post_mime_type', 'comment_count' );
+
+		foreach ( $post_fields as $pf ) {
+			$this->assertTrue( isset( $comment->$pf ), $pf );
+			$this->assertSame( $post->$pf, $comment->$pf, $pf );
+		}
+	}
 }

tests/phpunit/tests/comment/query.php

@@ -2108,4 +2108,41 @@ class Tests_Comment_Query extends WP_UnitTestCase {
 		// Direct descendants of $c2.
 		$this->assertEqualSets( array(), array_values( wp_list_pluck( $q->comments[ $c1 ]->get_child( $c2 )->get_children( $args ), 'comment_ID' ) ) );
 	}
+
+	/**
+	 * @ticket 27571
+	 */
+	public function test_update_comment_post_cache_should_be_disabled_by_default() {
+		global $wpdb;
+
+		$p = $this->factory->post->create();
+		$c = $this->factory->comment->create( array( 'comment_post_ID' => $p ) );
+
+		$q = new WP_Comment_Query( array(
+			'post_ID' => $p,
+		) );
+
+		$num_queries = $wpdb->num_queries;
+		$this->assertTrue( isset( $q->comments[0]->post_name ) );
+		$this->assertSame( $num_queries + 1, $wpdb->num_queries );
+	}
+
+	/**
+	 * @ticket 27571
+	 */
+	public function test_should_respect_update_comment_post_cache_true() {
+		global $wpdb;
+
+		$p = $this->factory->post->create();
+		$c = $this->factory->comment->create( array( 'comment_post_ID' => $p ) );
+
+		$q = new WP_Comment_Query( array(
+			'post_ID' => $p,
+			'update_comment_post_cache' => true,
+		) );
+
+		$num_queries = $wpdb->num_queries;
+		$this->assertTrue( isset( $q->comments[0]->post_name ) );
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+	}
 }