From 0338c8b3a3133198d76c27fadf8ab28ae3d71131 Mon Sep 17 00:00:00 2001
From: Boone Gorges <boonebgorges@git.wordpress.org>
Date: Tue, 23 Feb 2016 16:39:50 +0000
Subject: [PATCH] Query: Allow a seed value to be passed when using 'rand'
 `$orderby`.

`WP_Query` allows random ordering; `'orderby' => 'rand'` translates to
`ORDER BY RAND()`. This syntax results in random ordering that is not
consistent from request to request. MySQL supports the passing of a seed value
to random sorts, such as `ORDER BY RAND(3)`, which will return the same
random value each time it's called. `WP_Query` now supports this syntax, by
passing `RAND(3)` (or whatever integer seed value you'd like) as the value
of `'orderby'`.

Props hlashbrooke.
Fixes #35692.

git-svn-id: https://develop.svn.wordpress.org/trunk@36632 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/query.php          | 12 +++++++++++
 tests/phpunit/tests/post/query.php | 33 ++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/src/wp-includes/query.php b/src/wp-includes/query.php
index 70d02378d9..99df782336 100644
--- a/src/wp-includes/query.php
+++ b/src/wp-includes/query.php
@@ -1467,6 +1467,7 @@ class WP_Query {
 	 *              search terms, by prepending a hyphen.
 	 * @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.
 	 * @access public
 	 *
 	 * @param string|array $query {
@@ -1520,6 +1521,7 @@ class WP_Query {
 	 *                                                 specific `$meta_query` clause, use that clause's array key.
 	 *                                                 Default 'date'. Accepts 'none', 'name', 'author', 'date',
 	 *                                                 'title', 'modified', 'menu_order', 'parent', 'ID', 'rand',
+	 *                                                 'RAND(x)' (where 'x' is an integer seed value),
 	 *                                                 'comment_count', 'meta_value', 'meta_value_num', 'post__in',
 	 *                                                 and the array keys of `$meta_query`.
 	 *     @type int          $p                       Post ID.
@@ -2332,6 +2334,14 @@ class WP_Query {
 			$allowed_keys   = array_merge( $allowed_keys, array_keys( $meta_clauses ) );
 		}
 
+		// If RAND() contains a seed value, sanitize and add to allowed keys.
+		$rand_with_seed = false;
+		if ( preg_match( '/RAND\(([0-9]+)\)/i', $orderby, $matches ) ) {
+			$orderby = sprintf( 'RAND(%s)', intval( $matches[1] ) );
+			$allowed_keys[] = $orderby;
+			$rand_with_seed = true;
+		}
+
 		if ( ! in_array( $orderby, $allowed_keys, true ) ) {
 			return false;
 		}
@@ -2368,6 +2378,8 @@ class WP_Query {
 					// $orderby corresponds to a meta_query clause.
 					$meta_clause = $meta_clauses[ $orderby ];
 					$orderby_clause = "CAST({$meta_clause['alias']}.meta_value AS {$meta_clause['cast']})";
+				} elseif ( $rand_with_seed ) {
+					$orderby_clause = $orderby;
 				} else {
 					// Default: order by post field.
 					$orderby_clause = "$wpdb->posts.post_" . sanitize_key( $orderby );
diff --git a/tests/phpunit/tests/post/query.php b/tests/phpunit/tests/post/query.php
index bc0e865e47..357153847b 100644
--- a/tests/phpunit/tests/post/query.php
+++ b/tests/phpunit/tests/post/query.php
@@ -303,6 +303,39 @@ class Tests_Post_Query extends WP_UnitTestCase {
 		$this->assertNotContains( 'ASC', $q5->request );
 	}
 
+	/**
+	 * @ticket 35692
+	 */
+	public function test_orderby_rand_with_seed() {
+		$q = new WP_Query( array(
+			'orderby' => 'RAND(5)',
+		) );
+
+		$this->assertContains( 'ORDER BY RAND(5)', $q->request );
+	}
+
+	/**
+	 * @ticket 35692
+	 */
+	public function test_orderby_rand_should_ignore_invalid_seed() {
+		$q = new WP_Query( array(
+			'orderby' => 'RAND(foo)',
+		) );
+
+		$this->assertNotContains( 'ORDER BY RAND', $q->request );
+	}
+
+	/**
+	 * @ticket 35692
+	 */
+	public function test_orderby_rand_with_seed_should_be_case_insensitive() {
+		$q = new WP_Query( array(
+			'orderby' => 'rand(5)',
+		) );
+
+		$this->assertContains( 'ORDER BY RAND(5)', $q->request );
+	}
+
 	/**
 	 * Tests the post_name__in attribute of WP_Query.
 	 *