Kenapa tidak bisa panggil fungsi model dari controller?

class MY_Model extends CI_Model {
 
	/**
	 * The database table to use, only
	 * set if you want to bypass the magic
	 *
	 * @var string
	 */
	protected $_table;
 
	/**
	 * The primary key, by default set to
	 * `id`, for use in some functions.
	 *
	 * @var string
	 */
	protected $primary_key = 'id';
 
	/**
	 * An array of functions to be called before
	 * a record is created.
	 *
	 * @var array
	 */
	protected $before_create = array();
 
	/**
	 * An array of functions to be called after
	 * a record is created.
	 *
	 * @var array
	 */
	protected $after_create = array();
 
	/**
	 * An array of functions to be called before
	 * a record is retrieved.
	 *
	 * @var array
	 */
	protected $before_get = array();
 
	/**
	 * An array of functions to be called after
	 * a record is retrieved.
	 *
	 * @var array
	 */
	protected $after_get = array();
 
	/**
	 * An array of validation rules
	 *
	 * @var array
	 */
	protected $validate = array();
 
	/**
	 * Skip the validation
	 *
	 * @var bool
	 */
	protected $skip_validation = FALSE;
 
	/**
	 * Wrapper to __construct for when loading
	 * class is a superclass to a regular controller,
	 * i.e. - extends Base not extends Controller.
	 * 
	 * @return void
	 */
	public function MY_Model() { $this->__construct(); }
 
	/**
	 * The class constructer, tries to guess
	 * the table name.
	 */
	public function __construct() {
		parent::__construct();
 
		$this->load->helper('inflector');
 
		$this->_fetch_table();
	}
 
	/**
	 * Get a single record by creating a WHERE clause with
	 * a value for your primary key
	 *
	 * @param string $primary_value The value of your primary key
	 * @return object
	 */
	public function get($primary_value) {
		$this->_run_before_get();
		$row = $this->db->where($this->primary_key, $primary_value)
						->get($this->_table)
						->row();
		$this->_run_after_get($row);
		return $row;
	}
 
	/**
	 * Get a single record by creating a WHERE clause by passing
	 * through a CI AR where() call
	 *
	 * @param string $key The key to search by 
	 * @param string $val The value of that key
	 * @return object
	 */
	public function get_by() {
		$where =& func_get_args();
		$this->_set_where($where);
 
		$this->_run_before_get();
		$row = $this->db->get($this->_table)
						->row();
		$this->_run_after_get($row);
		return $row;
	}
 
	/**
	 * Similar to get(), but returns a result array of
	 * many result objects.
	 *
	 * @param string $key The key to search by
	 * @param string $values The value of that key
	 * @return array
	 */
	public function get_many($values) {
		$this->db->where_in($this->primary_key, $values);
 
		return $this->get_all();
	}
 
	/**
	 * Similar to get_by(), but returns a result array of
	 * many result objects.
	 *
	 * @param string $key The key to search by
	 * @param string $val The value of that key
	 * @return array
	 */
	public function get_many_by() {
		$where =& func_get_args();
		$this->_set_where($where);
 
		return $this->get_all();
	}
 
	/**
	 * Get all records in the database
	 *
	 * @return array
	 */
	public function get_all() {
		$this->_run_before_get();
		$result = $this->db->get($this->_table)
							->result();
		$this->_run_after_get($result);
		return $result;
	}
 
	/**
	 * Count the number of rows based on a WHERE
	 * criteria
	 *
	 * @param string $key The key to search by
	 * @param string $val The value of that key
	 * @return integer
	 */
	public function count_by() {
		$where =& func_get_args();
		$this->_set_where($where);
 
		return $this->db->count_all_results($this->_table);
	}
 
	/**
	 * Return a count of every row in the table
	 *
	 * @return integer
	 */
	public function count_all() {
		return $this->db->count_all($this->_table);
	}
 
	/**
	 * Insert a new record into the database,
	 * calling the before and after create callbacks.
	 * Returns the insert ID.
	 *
	 * @param array $data Information
	 * @return integer
	 */
	public function insert($data, $skip_validation = FALSE) {
		$valid = TRUE;
 
		if ($skip_validation === FALSE) {
			$valid = $this->_run_validation($data);
		}
 
		if($valid) {
			$data = $this->_run_before_create($data);
				$this->db->insert($this->_table, $data);
			$this->_run_after_create($data, $this->db->insert_id());
 
			return $this->db->insert_id();
		} else {
			return FALSE;
		}
	}
 
	/**
	 * Similar to insert(), just passing an array to insert
	 * multiple rows at once. Returns an array of insert IDs.
	 *
	 * @param array $data Array of arrays to insert
	 * @return array
	 */
	public function insert_many($data, $skip_validation = FALSE) {
		$ids = array();
 
		foreach ($data as $row) {
			$ids[] = $this->insert($row, $skip_validation);
		}
 
		return $ids;
	}
 
	/**
	 * Update a record, specified by an ID.
	 *
	 * @param integer $id The row's ID
	 * @param array $array The data to update
	 * @return bool
	 */
	public function update($primary_value, $data, $skip_validation = FALSE) {
		$valid = TRUE;
 
		if ($skip_validation === FALSE) {
			$valid = $this->_run_validation($data);
		}
 
		if ($valid) {
			return $this->db->where($this->primary_key, $primary_value)
							->set($data)
							->update($this->_table);
		} else {
			return FALSE;
		}
	}
 
	/**
	 * Update a record, specified by $key and $val.
	 *
	 * @param string $key The key to update with
	 * @param string $val The value
	 * @param array $array The data to update
	 * @return bool
	 */
	public function update_by() {
		$args =& func_get_args();
		$data = array_pop($args);
		$this->_set_where($args);
 
		if ($this->_run_validation($data)) {
			return $this->db->set($data)
							->update($this->_table);
		} else {
			return FALSE;
		}
	}
 
	/**
	 * Updates many records, specified by an array
	 * of IDs.
	 *
	 * @param array $primary_values The array of IDs
	 * @param array $data The data to update
	 * @return bool
	 */
	public function update_many($primary_values, $data, $skip_validation) {
		$valid = TRUE;
 
		if($skip_validation === FALSE) {
			$valid = $this->_run_validation($data);
		}
 
		if($valid) {
			return $this->db->where_in($this->primary_key, $primary_values)
							->set($data)
							->update($this->_table);
 
		} else {
			return FALSE;
		}
	}
 
	/**
	 * Updates all records
	 *
	 * @param array $data The data to update
	 * @return bool
	 */
	public function update_all($data)
	{
		return $this->db->set($data)
						->update($this->_table);
	}
 
	/**
	 * Delete a row from the database table by the
	 * ID.
	 *
	 * @param integer $id 
	 * @return bool
	 */
	public function delete($id) {
		return $this->db->where($this->primary_key, $id)
						->delete($this->_table);
	}
 
	/**
	 * Delete a row from the database table by the
	 * key and value.
	 *
	 * @param string $key
	 * @param string $value 
	 * @return bool
	 */
	public function delete_by() {
		$where =& func_get_args();
		$this->_set_where($where);
 
		return $this->db->delete($this->_table);
	}
 
	/**
	 * Delete many rows from the database table by 
	 * an array of IDs passed.
	 *
	 * @param array $primary_values 
	 * @return bool
	 */
	public function delete_many($primary_values) {
		return $this->db->where_in($this->primary_key, $primary_values)
						->delete($this->_table);
	}
 
	/**
	 * Retrieve and generate a dropdown-friendly array of the data
	 * in the table based on a key and a value.
	 *
	 * @return void
	 */
	function dropdown() {
		$args =& func_get_args();
 
		if(count($args) == 2) {
			list($key, $value) = $args;
		} else {
			$key = $this->primary_key;
			$value = $args[0];
		}
 
		$query = $this->db->select(array($key, $value))
						  ->get($this->_table);
 
		$options = array();
 
		foreach ($query->result() as $row) {
			$options[$row->{$key}] = $row->{$value};
		}
 
		return $options;
	}
 
	/**
	 * Orders the result set by the criteria,
	 * using the same format as CI's AR library.
	 *
	 * @param string $criteria The criteria to order by
	 * @return void
	 * @since 1.1.2
	 */
	public function order_by($criteria, $order = 'ASC') {
		$this->db->order_by($criteria, $order);
		return $this;
	}
 
	/**
	 * Limits the result set by the integer passed.
	 * Pass a second parameter to offset.
	 *
	 * @param integer $limit The number of rows
	 * @param integer $offset The offset
	 * @return void
	 * @since 1.1.1
	 */
	public function limit($limit, $offset = 0) {
		$this->db->limit($limit, $offset);
		return $this;
	}
 
	/**
	 * Tells the class to skip the insert validation
	 *
	 * @return void
	 */
	public function skip_validation() {
		$this->skip_validation = TRUE;
		return $this;
	}
 
	/**
	 * Runs the before create actions.
	 *
	 * @param array $data The array of actions
	 * @return void
	 */
	private function _run_before_create($data) {
		foreach ($this->before_create as $method) {
			$data = call_user_func_array(array($this, $method), array($data));
		}
 
		return $data;
	}
 
	/**
	 * Runs the after create actions.
	 *
	 * @param array $data The array of actions
	 * @return void
	 */
	private function _run_after_create($data, $id) {
		foreach ($this->after_create as $method) {
			call_user_func_array(array($this, $method), array($data, $id));
		}
	}
 
	/**
	 * Runs the before get actions.
	 *
	 * @return void
	 */
	private function _run_before_get()
	{
		foreach ($this->before_get as $method)
		{
			$this->$method();
		}
	}
 
	/**
	 * Runs the after get actions.
	 *
	 * @return void
	 */
	private function _run_after_get($result)
	{
		if($result === FALSE) return;
 
		if(!is_array($result)) $result = array($result);
 
		foreach($result as &$row){
			foreach ($this->after_get as $method)
			{
				call_user_func_array(array($this, $method), array($row));
			}
		}
	}
 
	/**
	 * Runs validation on the passed data.
	 *
	 * @return bool
	 */
	private function _run_validation($data) {
		if($this->skip_validation) {
			return TRUE;
		}
 
		if(!empty($this->validate)) {
			foreach($data as $key => $val) {
				$_POST[$key] = $val;
			}
 
			$this->load->library('form_validation');
 
			if(is_array($this->validate)) {
				$this->form_validation->set_rules($this->validate);
 
				return $this->form_validation->run();
			} else {
				return $this->form_validation->run($this->validate);
			}
		} else {
			return TRUE;
		}
	}
 
	/**
	 * Fetches the table from the pluralised model name.
	 *
	 * @return void
	 */
	private function _fetch_table() {
		if ($this->_table == NULL) {
			$class = preg_replace('/(_m|_model)?$/', '', get_class($this));
 
			$this->_table = plural(strtolower($class));
		}
	}
 
	/**
	 * Sets where depending on the number of parameters
	 *
	 * @return void
	 */
	private function _set_where($params) {
		if(count($params) == 1) {
			$this->db->where($params[0]);
		} else {
			$this->db->where($params[0], $params[1]);
		}
	}
}

class MY_Controller extends CI_Controller{
 
  var $ci;
  function __construct(){
    parent::__construct();
    $this->ci = &get_instance();
  }
 
  function showPage($content){
    $result = $this->ci->db_model->getAllData('QAMenu');
    $data['contents'] = $content;
    $data['title'] = 'ini adalah title';
    $data['nav_list'] = $result->result();
    $this->load->view('template', $data);
  }
 
}

$result = $this->menu_model->getMenu();

$this->load->model('menu_model');

class Menu extends CI_Controller{
  function __construct(){
    parent::__construct();
    $this->load->model('menu_model');
  }
 
  function index(){
    $result = $this->menu_model->getMenu();
  }
 
}

class menu_model extends CI_Model{
  function __construct(){
    parent::__construct();
  }
 
  function getMenu(){
    return 'ini menu';
  }
}