controller_test.php

<?php

class My_Controller extends Page_Controller
{
  
  private static $allowed_actions = array(
    'index',
    'TestFunction',
  );
  
  public function index(SS_HTTPRequest $request)
  {
    return array(
      'MyTemplateVar' => $this->TestFunction($request)
    );
  }
  
  public function TestFunction(SS_HTTPRequest $request)
  {
    $filter = ($request->getVar('f'))
      ? array('SomeAttribute' => explode(',' $request->getVar('f')))
      : array();
    
    $objects = MyObjet::get()->filter($filter);
    
    if($request->isAjax()){
      return $this->customise(
        array(
          'MyTemplateVar' => $objects
        )
      )->renderWith('MyCustomTemplate');
    }
    
    return $objects;
  }
  
}