如何使用codelgniter框架进行增删改查操作？

CREATE TABLE IF NOT EXISTS `users` (
 `id` int(10) NOT NULL AUTO_INCREMENT,
 `username` varchar(50) NOT NULL,
 `password` varchar(50) NOT NULL,
 `email` varchar(100) NOT NULL,
 `fullname` varchar(100) NOT NULL,
 PRIMARY KEY (`id`),
 UNIQUE KEY `username` (`username`),
 UNIQUE KEY `email` (`email`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

<?php
 class MTest extends CI_Model{
  public function __construct(){
   parent::__construct();
   $this->load->database();
  }
  //insert into data
  public function insert_users($arr){
   $this->db->insert('users',$arr);
  }
  //delete data
  public function delete_users($id){
   $this->db->where('id',$id);
   $this->db->delete('users');
  }
  //Alter data
  public function update_users($username,$arr){
   $this->db->where('username',$username);
   $this->db->update('users',$arr);
  }
  //select data
  public function select_users($id){
   $this->db->where('id',$id);
   $this->db->select('*');
   return $this->db->get('users');
   //注意如果你返回的是以下内容的话，他就是一个对象的结果集，这样当你返回controller中时，你就得转换；
//   return $query->result();
  }
 }
?>

<?php
/**
 * xxx.php
 * ==============================================
 * Copy right 2012-2015
 * ----------------------------------------------
 * This is not a free software, without any authorization is not allowed to use and spread.
 * ==============================================
 * @Author:YeXianMing
 * @Email:LangWaiShiGe@hotmail.com
 * @Version:zend studio10.6.2 php5.4.38 apache2.2
 */
 if(!defined('BASEPATH'))exit('No direct script access allowed');
 class Home extends CI_Controller{
  public function __construct(){
   parent::__construct();
  }
  //insert data
  public function insert(){
   $this->load->model('MTest','',TRUE);
   $arr=array('username'=>'yexianming1','password'=>'admin','email'=>'11504160314qq.com','fullname'=>'luotianyexianming');
   if(!($this->MTest->insert_users($arr))){
    echo "插入数据成功";
   }else{
    echo "插入数据失败";
   }
  }
  //update data
  public function update(){
   $this->load->model('MTest','',TRUE);
   $arr=array('username'=>'Helloworld22','password'=>'root','email'=>'895787704@qq.com','fullname'=>'luotianyecong');
   if(!($this->MTest->update_users('Helloworld',$arr))){
    echo "修改成功";
   }else{
    echo "修改失败";
   }
  }
  //delete data
  public function delete(){
   $this->load->model('MTest','',TRUE);
   $query=$this->MTest->delete_users(12);
   if(!$query){
    echo "删除成功";
   }else{
    echo "删除失败";
   }
  }
  //select data
  public function select(){
   $this->load->library('table');
   $this->load->model('MTest','',TRUE);
   $arr=$this->MTest->select_users(3);
   $userinformation=$this->table->generate($arr);
   $data['userinfor']=$userinformation;
   $this->load->view('template',$data);
  }
 }
?>

<?php echo $userinfor;?>

id username password email fullname
3 Helloworld22 root 1111111@qq.com luotianyecong