public function addClass($class, $options = array())
    {
        if ($this->fulltextFields || $this->filterFields || $this->sortFields) {
            throw new Exception('Can\'t add class to Index after fields have already been added');
        }

        $options = array_merge(array(
            'include_children' => true
        ), $options);

        $this->classes[$class] = $options;
    }