Refactor WP_Query to ensure consistent ordering by appending ID as a secondary sort field in various scenarios. Update unit tests to reflect changes in expected SQL output for orderby cases, enhancing determinism in query results.

Author: ramonjd

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

@@ -2595,7 +2595,7 @@ public function get_posts() {
 			if ( empty( $orderby_array ) ) {
 				$orderby = "{$wpdb->posts}.post_date " . $query_vars['order'] . ', ' . "{$wpdb->posts}.ID " . $query_vars['order'];
 			} else {
-				$orderby = implode( ', ', $orderby_array );
+				$orderby = trim( implode( ', ', $orderby_array ) );
 			}
 		}
 
@@ -3311,7 +3311,18 @@ public function get_posts() {
 		}
 
 		if ( $query_vars['cache_results'] && $id_query_is_cacheable ) {
-			$new_request = str_replace( $fields, "{$wpdb->posts}.*", $this->request );
+			$new_request = $this->request;
+			// Split SQL into parts.
+			$parts = explode( 'ORDER BY', $new_request );
+			if ( count( $parts ) === 2 ) {
+				// Replace only in the SELECT part, preserve ORDER BY.
+				$select_part = str_replace( $fields, "{$wpdb->posts}.*", $parts[0] );
+				$new_request = $select_part . 'ORDER BY' . $parts[1];
+			} else {
+				// No ORDER BY clause, safe to replace.
+				$new_request = str_replace( $fields, "{$wpdb->posts}.*", $new_request );
+			}
+
 			$cache_key   = $this->generate_cache_key( $query_vars, $new_request );
 
 			$cache_found = false;
@@ -5099,8 +5110,8 @@ protected function generate_cache_key( array $args, $sql ) {
 		}
 
 		// Add a default orderby value of date to ensure same cache key generation.
-		if ( ! isset( $q['orderby'] ) ) {
-			$args['orderby'] = 'date';
+		if ( ! isset( $args['orderby'] ) ) {
+			$args['orderby'] = 'date, ID';
 		}
 
 		$placeholder = $wpdb->placeholder_escape();

tests/phpunit/tests/rest-api/rest-posts-controller.php

@@ -488,7 +488,7 @@ public function test_get_items_include_query( $method ) {
 			$this->assertSame( 2, $headers['X-WP-Total'], 'Failed asserting that the number of posts is correct.' );
 		}
 
-		$this->assertPostsOrderedBy( '{posts}.post_date DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_date DESC, {posts}.ID DESC' );
 
 		// 'orderby' => 'include'.
 		$request->set_param( 'orderby', 'include' );
@@ -544,7 +544,7 @@ public function test_get_items_orderby_author_query() {
 		$this->assertSame( self::$editor_id, $data[1]['author'] );
 		$this->assertSame( self::$editor_id, $data[2]['author'] );
 
-		$this->assertPostsOrderedBy( '{posts}.post_author DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_author DESC, {posts}.ID DESC' );
 	}
 
 	public function test_get_items_orderby_modified_query() {
@@ -568,7 +568,7 @@ public function test_get_items_orderby_modified_query() {
 		$this->assertSame( $id3, $data[1]['id'] );
 		$this->assertSame( $id2, $data[2]['id'] );
 
-		$this->assertPostsOrderedBy( '{posts}.post_modified DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_modified DESC, {posts}.ID DESC' );
 	}
 
 	public function test_get_items_orderby_parent_query() {
@@ -606,7 +606,7 @@ public function test_get_items_orderby_parent_query() {
 		$this->assertSame( 0, $data[1]['parent'] );
 		$this->assertSame( 0, $data[2]['parent'] );
 
-		$this->assertPostsOrderedBy( '{posts}.post_parent DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_parent DESC, {posts}.ID DESC' );
 	}
 
 	public function test_get_items_exclude_query() {
@@ -976,14 +976,14 @@ public function test_get_items_order_and_orderby() {
 		$response = rest_get_server()->dispatch( $request );
 		$data     = $response->get_data();
 		$this->assertSame( 'Apple Sauce', $data[0]['title']['rendered'] );
-		$this->assertPostsOrderedBy( '{posts}.post_title DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_title DESC, {posts}.ID DESC' );
 
 		// 'order' => 'asc'.
 		$request->set_param( 'order', 'asc' );
 		$response = rest_get_server()->dispatch( $request );
 		$data     = $response->get_data();
 		$this->assertSame( 'Apple Cobbler', $data[0]['title']['rendered'] );
-		$this->assertPostsOrderedBy( '{posts}.post_title ASC' );
+		$this->assertPostsOrderedBy( '{posts}.post_title ASC, {posts}.ID ASC' );
 
 		// 'order' => 'asc,id' should error.
 		$request->set_param( 'order', 'asc,id' );
@@ -1068,7 +1068,7 @@ public function test_get_items_with_orderby_slug() {
 		// Default ORDER is DESC.
 		$this->assertSame( 'xyz', $data[0]['slug'] );
 		$this->assertSame( 'abc', $data[1]['slug'] );
-		$this->assertPostsOrderedBy( '{posts}.post_name DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_name DESC, {posts}.ID DESC' );
 	}
 
 	public function test_get_items_with_orderby_slugs() {
@@ -1120,7 +1120,7 @@ public function test_get_items_with_orderby_relevance() {
 		$this->assertCount( 2, $data );
 		$this->assertSame( $id1, $data[0]['id'] );
 		$this->assertSame( $id2, $data[1]['id'] );
-		$this->assertPostsOrderedBy( '{posts}.post_title LIKE \'%relevant%\' DESC, {posts}.post_date DESC' );
+		$this->assertPostsOrderedBy( '{posts}.post_title LIKE \'%relevant%\' DESC, {posts}.post_date DESC, {posts}.ID DESC' );
 	}
 
 	public function test_get_items_with_orderby_relevance_two_terms() {
@@ -1148,7 +1148,7 @@ public function test_get_items_with_orderby_relevance_two_terms() {
 		$this->assertCount( 2, $data );
 		$this->assertSame( $id1, $data[0]['id'] );
 		$this->assertSame( $id2, $data[1]['id'] );
-		$this->assertPostsOrderedBy( '(CASE WHEN {posts}.post_title LIKE \'%relevant content%\' THEN 1 WHEN {posts}.post_title LIKE \'%relevant%\' AND {posts}.post_title LIKE \'%content%\' THEN 2 WHEN {posts}.post_title LIKE \'%relevant%\' OR {posts}.post_title LIKE \'%content%\' THEN 3 WHEN {posts}.post_excerpt LIKE \'%relevant content%\' THEN 4 WHEN {posts}.post_content LIKE \'%relevant content%\' THEN 5 ELSE 6 END), {posts}.post_date DESC' );
+		$this->assertPostsOrderedBy( '(CASE WHEN {posts}.post_title LIKE \'%relevant content%\' THEN 1 WHEN {posts}.post_title LIKE \'%relevant%\' AND {posts}.post_title LIKE \'%content%\' THEN 2 WHEN {posts}.post_title LIKE \'%relevant%\' OR {posts}.post_title LIKE \'%content%\' THEN 3 WHEN {posts}.post_excerpt LIKE \'%relevant content%\' THEN 4 WHEN {posts}.post_content LIKE \'%relevant content%\' THEN 5 ELSE 6 END), {posts}.post_date DESC, {posts}.ID DESC' );
 	}
 
 	public function test_get_items_with_orderby_relevance_missing_search() {