[wp-trac] [WordPress Trac] #20236: Improper testing of cache retrievals causes wasted queries.

[WordPress Trac]

#20236: Improper testing of cache retrievals causes wasted queries.
--------------------------+-----------------------------
 Reporter:  andy          |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  General       |    Version:
 Severity:  normal        |   Keywords:
--------------------------+-----------------------------
 `wp_cache_get()` can retrieve values such as the empty array which is
 considered false by the `!` test. The following function is incorrect
 because it will always ignore the cache and repeat the `get_col` and
 `wp_cache_add` when the cache contains the empty array. This occurs on
 sites which have no pages.

 {{{
 function get_all_page_ids() {
         global $wpdb;

         if ( ! $page_ids = wp_cache_get('all_page_ids', 'posts') ) {
                 $page_ids = $wpdb->get_col("SELECT ID FROM $wpdb->posts
 WHERE post_type = 'page'");
                 wp_cache_add('all_page_ids', $page_ids, 'posts');
         }

         return $page_ids;
 }
 }}}

 The cache check should be written with an understanding of the return type
 of `$wpdb->get_col()` (array). Here it is with the check fixed:

 {{{
 function get_all_page_ids() {
         global $wpdb;

         $page_ids = wp_cache_get('all_page_ids', 'posts');
         if ( ! is_array( $page_ids ) ) {
                 $page_ids = $wpdb->get_col("SELECT ID FROM $wpdb->posts
 WHERE post_type = 'page'");
                 wp_cache_add('all_page_ids', $page_ids, 'posts');
         }

         return $page_ids;
 }
 }}}

 Patch 1 fixes this occurrence. Please keep this ticket open until all
 similar occurrences are found and fixed.

-- 
Ticket URL: <http://core.trac.wordpress.org/ticket/20236>
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