Order by custom field (numeric) in WP_Query

Question

I am using following query to get all posts with post_type 'portfolio'.

$args = array( 
           'posts_per_page' => -1, 
           'offset'=> 0,
           'post_type' => 'portfolio'
         );

$all_posts = new WP_Query($args);

Where $args is:

$args = array( 
               'posts_per_page' => -1, 
               'offset'=> 0,
               'post_type' => 'portfolio',
               'orderby' => 'up_count', //up_count is numeric field from posts table
               'order' => DESC
             );

This should sort the results by up_count. But that's not the case. The codex for wp_query doesn't clearly state about sorting with custom field (or may be I am missing something?).

This is the query I get when debugging wp_query request.

SELECT ap_posts.* FROM ap_posts  WHERE 1=1  AND ap_posts.post_type = 'portfolio' AND (ap_posts.post_status = 'publish' OR ap_posts.post_status = 'private')  ORDER BY ap_posts.post_date DESC  

EDIT: up_count is an extra field of type int in table posts table.

P.S. I am using wordpress ver. 3.5.2

Answer 1

WP_Query Arguments should be:

$args = array( 
    'posts_per_page' => -1, 
    'offset'         => 0,    
    'post_type'      => 'portfolio',
    'meta_key'       => 'up_count',
    'orderby'        => 'meta_value_num',
    'order'          => 'DESC'
);

All this is written in the Codex, but you need to read many times to understand.