title: Wordpress, multiple meta_key in pre_get_posts
body: <p>is it possible to add two <code>meta_key's</code> in <code>pre_get_posts</code>?</p>
  
  <p><strong>my current query</strong></p>
  
  <pre><code>$query-&gt;set('s', '' ); 
  $query-&gt;set( 'meta_key', 'cat_adresse_stadtteil' );
  $query-&gt;set( 'meta_value', array('charlottenburg', 'wilmersdorf', 'schmargendorf') ); 
  </code></pre>
  
  <p><strong>add this</strong></p>
  
  <pre><code>$query-&gt;set('orderby','meta_value_num');
  $query-&gt;set('meta_key', 'rank');
  $query-&gt;set('order', 'ASC');  
  </code></pre>
  
  <p><br /><br />
  <strong>EDIT</strong><br />
  Ok, i found this solution (<a href="http://www.advancedcustomfields.com/resources/how-to-query-posts-filtered-by-custom-field-values/">link</a> #example 2)</p>
  
  <pre><code>$args = array(
      'numberposts' =&gt; -1,
      'post_type' =&gt; 'event',
      'meta_query' =&gt; array(
          'relation' =&gt; 'AND',
          array(
              'key' =&gt; 'location',
              'value' =&gt; 'Melbourne',
              'compare' =&gt; '='
          ),
          array(
              'key' =&gt; 'attendees',
              'value' =&gt; 100,
              'type' =&gt; 'NUMERIC',
              'compare' =&gt; '&gt;'
          )
      )
  );
  </code></pre>
  
  <p>but it doesnt work, any ideas what is wrong?</p>
  
  <pre><code>$query-&gt;set('meta_query',array(
               array( 'key' =&gt; 'cat_adresse_stadtteil',
                      'value' =&gt; array('charlottenburg', 'wilmersdorf', 'schmargendorf'), ),
              array(  'key' =&gt; 'rank'
                      'orderby' =&gt; 'meta_value_num',
                      'order' =&gt; 'ASC' ) ) ); 
  </code></pre>