public function limit($offset = null, $limit = null)
    {
    	$args = func_get_args();
    	if (count($args) === 0) {
    		throw new Exception('At least 1 argument');
    	}
    	if (count($args) == 1) {
    		$this->limit =  $args[0];
    	} else {
    		list($this->offset, $this->limit) = $args;
    	}
        return $this;
    }