def get_controller_by_id(self, id):
        """Get the controller object given the id.

        This method returns the controller object for given id.

        :param id: id of the controller, for example
            'Smart Array P822 in Slot 2'
        :returns: Controller object which has the id or None if the
            controller is not found.
        """
        for controller in self.controllers:
            if controller.id == id:
                return controller
        return None