title: WordPress WP_Query: Display custom post type based on custom meta value, and also order on another custom meta value
body: <p>I am using the WordPress plug-ins <a href="http://www.advancedcustomfields.com/" rel="nofollow">Advanced Custom Fields</a>, and <a href="http://webdevstudios.com/plugin/custom-post-type-ui/" rel="nofollow">Custom Post Type UI</a>.</p>
  
  <p>I have built a WP_Query to display a particular post type, filtered by a particular custom field value.</p>
  
  <pre><code>$loop = new WP_Query( array( 
      'post_type' =&gt; 'news', 
      'meta_key' =&gt; 'news_story_type', 
      'meta_value' =&gt; 'release', 
      'posts_per_page' =&gt; 3 
  ) );
  </code></pre>
  
  <p>I now want to sort the resulting posts by another custom field, <code>date_of_publication</code> rather than use WordPress's menu_order or date. The <a href="http://www.advancedcustomfields.com/resources/how-to/orde-posts-by-custom-fields/" rel="nofollow">ACF documentation</a> says to specify <code>orderby</code> and <code>meta_key</code> in the query args. </p>
  
  <blockquote>
    <p>$args = array(</p>
    
    <p>'post_type'     => 'event',</p>
    
    <p>'posts_per_page'    => -1,</p>
    
    <p>'meta_key'      => 'start_date',</p>
    
    <p>'orderby'       => 'meta_value_num',</p>
    
    <p>'order'         => 'DESC' );</p>
  </blockquote>
  
  <p>But alas, doing so conflicts with the <code>meta_key</code> I've already supplied to filter.</p>
  
  <p>Has anyone encountered this before and found a solution?</p>