My_Model - CodeIgniter

<?php

class My_Model extends CI_Model{
     protected $_table_name     = '';
     protected $_primary_key    = '';
     protected $_order_by       ;
     protected $_filter         = 'intval';
     protected $rules           = array();
     protected $_timestamp      = FALSE;

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

     public function get($id = null , $single = false){
         if($id!=NULL){
             $filter = $this->_filter;
             $id = $filter($id);
             $this->db->where($this->_primary_key,$id);
             $method = 'first_row';
         }else if($single){
             $method = 'first_row';
         }else{
             $method = 'result_array';
         }

         return $this->db->get($this->_table_name)->$method();
     }

     public function get_by($where , $single = false){

         $this->db->where($where);
         return $this->get(NULL , $single);
     }

     public function save($data , $id=NULL){
         if($this->_timestamp){
             $now = date('Y-m-d H:i:s');
             $id || $data['created'] = $now;
             $data['modified'] = $now;
         }
         if($id === NULL){
             // Inserer un nouveau enregistrement
             !isset($data[$this->_primary_key]) || $data[$this->_primary_key] = NULL;
             $this->db->set($data);
             $this->db->insert($this->_table_name);
             $this->db->insert_id();
         }else{
             // update
             $filter = $this->_filter;
             $id = $filter($id);
             $this->db->set($data);
             $this->db->where($this->_primary_key,$id);
             $this->db->update($this->_table_name);
         }

        return $id;
     }

     public function delete($id=null){
        if(!$this->get($id))
            return false;
         $filter = $this->_filter;
         $id = $filter($id);
         if(!$id){
             return false;
         }
         $this->db->where($this->_primary_key,$id);
         $this->db->limit(1);
         $this->db->delete($this->_table_name);
         return true;
     }
}