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<title>[59993] trunk: Query: Fix performance regression starting the loop for `all` fields.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/59993">59993</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/59993","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>peterwilsoncc</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2025-03-16 22:55:11 +0000 (Sun, 16 Mar 2025)</dd>
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<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Query: Fix performance regression starting the loop for `all` fields.

Fixes a performance regression starting the loop after calling `WP_Query( [ 'fields' => 'all' ] )`. This changes how `WP_Query::the_post()` determines whether there is a need to traverse the posts for cache warming.

If IDs are queried, `WP_Query::$posts` is assumed to be an array of post IDs. If all fields are queried, `WP_Query::$posts` is assumed to be an array of fully populated post objects.

Follow up to <a href="https://core.trac.wordpress.org/changeset/59919">[59919]</a>, <a href="https://core.trac.wordpress.org/changeset/59937">[59937]</a>.

Props joemcgill, peterwilsoncc, SirLouen.
Fixes <a href="https://core.trac.wordpress.org/ticket/56992">#56992</a>.</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludesclasswpqueryphp">trunk/src/wp-includes/class-wp-query.php</a></li>
<li><a href="#trunktestsphpunittestsquerythePostphp">trunk/tests/phpunit/tests/query/thePost.php</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunksrcwpincludesclasswpqueryphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/class-wp-query.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/class-wp-query.php  2025-03-16 22:47:49 UTC (rev 59992)
+++ trunk/src/wp-includes/class-wp-query.php    2025-03-16 22:55:11 UTC (rev 59993)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -2067,6 +2067,15 @@
</span><span class="cx" style="display: block; padding: 0 10px">                        case 'id=>parent':
</span><span class="cx" style="display: block; padding: 0 10px">                                $fields = "{$wpdb->posts}.ID, {$wpdb->posts}.post_parent";
</span><span class="cx" style="display: block; padding: 0 10px">                                break;
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+                        case '':
+                               /*
+                                * Set the default to 'all'.
+                                *
+                                * This is used in `WP_Query::the_post` to determine if the
+                                * entire post object has been queried.
+                                */
+                               $q['fields'] = 'all';
+                               // Falls through.
</ins><span class="cx" style="display: block; padding: 0 10px">                         default:
</span><span class="cx" style="display: block; padding: 0 10px">                                $fields = "{$wpdb->posts}.*";
</span><span class="cx" style="display: block; padding: 0 10px">                }
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -3739,28 +3748,30 @@
</span><span class="cx" style="display: block; padding: 0 10px">                global $post;
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px">                if ( ! $this->in_the_loop ) {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-                        // Get post IDs to prime incomplete post objects.
-                       $post_ids = array_reduce(
-                               $this->posts,
-                               function ( $carry, $post ) {
-                                       if ( is_numeric( $post ) && $post > 0 ) {
-                                               // Query for post ID.
-                                               $carry[] = $post;
-                                       }
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+                 if ( 'all' === $this->query_vars['fields'] ) {
+                               // Full post objects queried.
+                               $post_objects = $this->posts;
+                       } else {
+                               if ( 'ids' === $this->query_vars['fields'] ) {
+                                       // Post IDs queried.
+                                       $post_ids = $this->posts;
+                               } else {
+                                       // Only partial objects queried, need to prime the cache for the loop.
+                                       $post_ids = array_reduce(
+                                               $this->posts,
+                                               function ( $carry, $post ) {
+                                                       if ( isset( $post->ID ) ) {
+                                                               $carry[] = $post->ID;
+                                                       }
</ins><span class="cx" style="display: block; padding: 0 10px"> 
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-                                        if ( is_object( $post ) && isset( $post->ID ) ) {
-                                               // Query for object, either WP_Post or stdClass.
-                                               $carry[] = $post->ID;
-                                       }
-
-                                       return $carry;
-                               },
-                               array()
-                       );
-                       if ( $post_ids ) {
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+                                                 return $carry;
+                                               },
+                                               array()
+                                       );
+                               }
</ins><span class="cx" style="display: block; padding: 0 10px">                                 _prime_post_caches( $post_ids, $this->query_vars['update_post_term_cache'], $this->query_vars['update_post_meta_cache'] );
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+                                $post_objects = array_map( 'get_post', $post_ids );
</ins><span class="cx" style="display: block; padding: 0 10px">                         }
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-                        $post_objects = array_map( 'get_post', $post_ids );
</del><span class="cx" style="display: block; padding: 0 10px">                         update_post_author_caches( $post_objects );
</span><span class="cx" style="display: block; padding: 0 10px">                }
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -3781,12 +3792,19 @@
</span><span class="cx" style="display: block; padding: 0 10px">                $post = $this->next_post();
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px">                // Ensure a full post object is available.
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-                if ( $post instanceof stdClass ) {
-                       // stdClass indicates that a partial post object was queried.
-                       $post = get_post( $post->ID );
-               } elseif ( is_numeric( $post ) ) {
-                       // Numeric indicates that only post IDs were queried.
-                       $post = get_post( $post );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+         if ( 'all' !== $this->query_vars['fields'] ) {
+                       if ( 'ids' === $this->query_vars['fields'] ) {
+                               // Post IDs queried.
+                               $post = get_post( $post );
+                       } elseif ( isset( $post->ID ) ) {
+                               /*
+                                * Partial objecct queried.
+                                *
+                                * The post object was queried with a partial set of
+                                * fields, populate the entire object for the loop.
+                                */
+                               $post = get_post( $post->ID );
+                       }
</ins><span class="cx" style="display: block; padding: 0 10px">                 }
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px">                // Set up the global post object for the loop.
</span></span></pre></div>
<a id="trunktestsphpunittestsquerythePostphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/phpunit/tests/query/thePost.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/phpunit/tests/query/thePost.php       2025-03-16 22:47:49 UTC (rev 59992)
+++ trunk/tests/phpunit/tests/query/thePost.php 2025-03-16 22:55:11 UTC (rev 59993)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -49,6 +49,86 @@
</span><span class="cx" style="display: block; padding: 0 10px">        }
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px">        /**
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+         * Ensure custom 'fields' values are respected.
+        *
+        * @ticket 56992
+        */
+       public function test_wp_query_respects_custom_fields_values() {
+               global $wpdb;
+               add_filter(
+                       'posts_fields',
+                       function ( $fields, $query ) {
+                               global $wpdb;
+
+                               if ( $query->get( 'fields' ) === 'custom' ) {
+                                       $fields = "$wpdb->posts.ID,$wpdb->posts.post_author";
+                               }
+
+                               return $fields;
+                       },
+                       10,
+                       2
+               );
+
+               $query = new WP_Query(
+                       array(
+                               'fields'    => 'custom',
+                               'post_type' => 'page',
+                               'post__in'  => self::$page_child_ids,
+                       )
+               );
+
+               $this->assertNotEmpty( $query->posts, 'The query is expected to return results' );
+               $this->assertSame( $query->get( 'fields' ), 'custom', 'The WP_Query class is expected to use the custom fields value' );
+               $this->assertStringContainsString( "$wpdb->posts.ID,$wpdb->posts.post_author", $query->request, 'The database query is expected to use the custom fields value' );
+       }
+
+       /**
+        * Ensure custom 'fields' populates the global post in the loop.
+        *
+        * @ticket 56992
+        */
+       public function test_wp_query_with_custom_fields_value_populates_the_global_post() {
+               global $wpdb;
+               add_filter(
+                       'posts_fields',
+                       function ( $fields, $query ) {
+                               global $wpdb;
+
+                               if ( $query->get( 'fields' ) === 'custom' ) {
+                                       $fields = "$wpdb->posts.ID,$wpdb->posts.post_author";
+                               }
+
+                               return $fields;
+                       },
+                       10,
+                       2
+               );
+
+               $query = new WP_Query(
+                       array(
+                               'fields'    => 'custom',
+                               'post_type' => 'page',
+                               'post__in'  => self::$page_child_ids,
+                               'orderby'   => 'id',
+                               'order'     => 'ASC',
+                       )
+               );
+
+               $query->the_post();
+
+               // Get the global post and specific post.
+               $global_post   = get_post();
+               $specific_post = get_post( self::$page_child_ids[0], ARRAY_A );
+
+               $this->assertSameSetsWithIndex( $specific_post, $global_post->to_array(), 'The global post is expected to be fully populated.' );
+
+               $this->assertNotEmpty( get_the_title(), 'The title is expected to be populated.' );
+               $this->assertNotEmpty( get_the_content(), 'The content is expected to be populated.' );
+               $this->assertNotEmpty( get_the_excerpt(), 'The excerpt is expected to be populated.' );
+       }
+
+       /**
</ins><span class="cx" style="display: block; padding: 0 10px">          * Ensure that a secondary loop populates the global post completely regardless of the fields parameter.
</span><span class="cx" style="display: block; padding: 0 10px">         *
</span><span class="cx" style="display: block; padding: 0 10px">         * @ticket 56992
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -75,11 +155,11 @@
</span><span class="cx" style="display: block; padding: 0 10px">                $global_post   = get_post();
</span><span class="cx" style="display: block; padding: 0 10px">                $specific_post = get_post( self::$page_child_ids[0], ARRAY_A );
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+                $this->assertSameSetsWithIndex( $specific_post, $global_post->to_array(), 'The global post is expected to be fully populated.' );
+
</ins><span class="cx" style="display: block; padding: 0 10px">                 $this->assertNotEmpty( get_the_title(), 'The title is expected to be populated.' );
</span><span class="cx" style="display: block; padding: 0 10px">                $this->assertNotEmpty( get_the_content(), 'The content is expected to be populated.' );
</span><span class="cx" style="display: block; padding: 0 10px">                $this->assertNotEmpty( get_the_excerpt(), 'The excerpt is expected to be populated.' );
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-
-               $this->assertSameSetsWithIndex( $specific_post, $global_post->to_array(), 'The global post is expected to be fully populated.' );
</del><span class="cx" style="display: block; padding: 0 10px">         }
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px">        /**
</span></span></pre>
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