public function facets($facets)
    {
        $this->params['facets'] = array();
        if (is_array($facets)){
            $args = $facets;
        }else{
            $args = func_get_args();
        }
        foreach ($args as $arg) {
            if ($arg instanceof FacetInterface) {
                $this->params['facets'][] = $arg;
            }
        }

        return $this;
    }