title: Wordpress search custom fields
body: <p>I have a custom field with meta_name is product_id. I am trying to determine how to search that field when using the wordpress search. </p>
  
  <p>I know the wordpress search results page uses query_string which contains the "s" value for the keyword searched I just don't know how to change my code below to search the custom field mentioned.</p>
  
  <pre><code>$loop = new WP_Query("$query_string . '&amp;posts_per_page=-1&amp;post_type=product'"); ?&gt; 
  </code></pre>