how to delete all user roles? Need ORM changes

orm-remove.php

/**
	 * Removes a relationship between this model and another (or delete all relationships).
	 *
	 * @param   string   alias of the has_many "through" relationship
	 * @param   mixed    related ORM model or NULL to clear relationship
	 * @return  ORM
	 */
	public function remove($alias, ORM $model = NULL)
	{
		$query = DB::delete($this->_has_many[$alias]['through'])
			->where($this->_has_many[$alias]['foreign_key'], '=', $this->pk());

		if ( ! is_null($model))
		{
			// delete $model only
			$query->where($this->_has_many[$alias]['far_key'], '=', $model->pk());
		}

		$query->execute($this->_db);

		return $this;
	}