Codeigniter MY_Model on core folder

MY_Model.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');


class MY_Model extends CI_Model {

  public $error_string, $new_id;

	function __construct()
	{
		parent::__construct();
	}

	/*
	| -------------------------------------------------------------------------
	| Generic functions
	| -------------------------------------------------------------------------
	*/

	function Update($table, $primary_key, $primary_value, $data, $form_set=array())
	{
		$this->db->where($primary_key, $primary_value);
		
		if(! empty($form_set))
		{
			foreach($form_set as $key=>$val)
			{
				$this->db->set($key,$val,false);
			}
		}
		
		if ($this->db->update($table, $data))
		{
			return TRUE;
		}else{
			$this->error_string = mysql_error();
			return FALSE;
		}
	}
	
	function Insert($table, $form_data, $form_set=array())
	{
		if(! empty($form_set))
		{
			foreach($form_set as $key=>$val)
			{
				$this->db->set($key,$val,false);
			}
		}
		if ($this->db->insert($table, $form_data))
		{
            $this->new_id = $this->db->insert_id();
			return TRUE;
		}else{
			$this->error_string = mysql_error();
			return FALSE;
		}
	}
		
	function Delete($table, $primary_key, $primary_value, $where = false)
	{
		if ($this->db->delete($table, array($primary_key => $primary_value)))
		{
			return TRUE;
		}else{
			$this->error_string = mysql_error();
			return FALSE;
		}
	}
	
	function Select($table,$param = array())
	{
		
		if(isset($param['select']))
		{
			$this->db->select($param['select']);
		}	
		if(isset($param['where']))
		{
			$this->db->where($param['where']);
		}
		if(isset($param['order']))
		{
			$this->db->order_by($param['order']['name'],$param['order']['type']);
		}
		if(isset($param['limit']))
		{
			if(isset($param['offset']))
			{
				$this->db->limit($param['limit'],$param['offset']);
			}else{
				$this->db->limit($param['limit']);
			}
		}
      
        if(isset($param['like']))
        { 
            foreach($param['like'] as $key=>$val)
            {
                $this->db->like($key,$val);
            }
        }
        
		$res = $this->db->get($table);
		//test($this->db->getSQL()); //exit;
		
		if($res->num_rows() > 0)
		{
			return $res->result_array();
		}else{
			return false;
		}
	}

	function SelectOne($table,$param = array())
	{
		$param['limit'] = 1;
		$data = $this->Select($table,$param); 
		if(! empty($data)) return $data[0];
		return false;
	}
	
	function returnQuery($sql)
	{
		$res = $this->db->query($sql);
		if($res->num_rows() > 0)
		{
			return $res->result_array();
		}else{
			return false;
		}
	}
	
	function doQuery($sql)
	{
		return $this->db->query($sql);	
	}	
	
	
	
}