title: zf2 : select columns dont work on tablegateway
body: <p>I created the method 'fetchAll()' in my model in this way</p>
  
  <pre><code>public function fetchAll(){
  
      $resultSet = $this-&gt;tableGateway-&gt;select( function (Select $select) {
  
          $select-&gt;columns(array('my_alias'=&gt;'my_field'));
  
      });
  
      return $resultSet;
  
  }
  </code></pre>
  
  <p>so, i get the results in controller</p>
  
  <pre><code>...
  
  $items = $this-&gt;getMyTable()-&gt;fetchAll();
  
  ...
  </code></pre>
  
  <p>and i sendo to my action</p>
  
  <pre><code>...
  
  foreach( $items =&gt; $item ){ print $item-&gt;my_alias; } 
  
  ...
  </code></pre>
  
  <p>but '$item->my_alias' is not defined. Without 'columns' method, its work. Whats wrong ?</p>