php單例模式封裝數據庫操做類增刪改查

<?php//三私一公 單例class Db{   //數據庫鏈接對象   private static $instance;   private static $table_name;   private $pdo;   //防止類直接實例化   private function __construct(){      $this->pdo = new PDO("mysql:host=127.0.0.1;dbname=test_system", "root", "");      $this->pdo->query("set names utf8");   }   //禁止克隆對象   private function __clone(){}   //返回數據庫實例對象   public static function getDb($table_name){      self::$table_name = $table_name;      if(!(self::$instance instanceof self)){         self::$instance = new self;      }      return self::$instance;   }   function add($table_name, $data){      $keys = implode(",", array_keys($data));      $value = "'".implode("','", array_values($data))."'";      $sql = "insert into $table_name ($keys) values($value) ";      $r = $this->pdo->exec($sql);      $this->getErrorInfo();      return $r;   }   function addAll($table_name, $data){      $keys = implode(",", array_keys($data[0]));      $arr = [];      foreach ($data as $k => $v) {         $arr[] = "('".implode("','", array_values($v))."')";      }      $value = implode(",", $arr);      $sql = "insert into $table_name ($keys) values $value";      $r = $this->pdo->exec($sql);      $this->getErrorInfo();      return $r;   }   function update($table_name, $data){      $id = $data['id'];      unset($data['id']);      $arr = [];      foreach($data as $k=>$v){         $arr[] = $k."='".$v ."'";      }      $str = implode(",", $arr);      $sql = "update $table_name set $str where id=$id";      $r = $this->pdo->exec($sql);      $this->getErrorInfo();      return $r;   }   function select($table_name, $where = '1=1'){      $sql = "select * from $table_name where $where ";      $res = $this->pdo->query($sql)->fetchAll(PDO::FETCH_ASSOC);      $this->getErrorInfo();      return $res;   }   function find($table_name, $where = '1=1'){      $sql = "select * from $table_name where $where ";      $res = $this->pdo->query($sql)->fetch(PDO::FETCH_ASSOC);      $this->getErrorInfo();      return $res;   }   function getErrorInfo(){      if($this->pdo->errorCode() != '00000'){         echo "<pre>";         print_r($this->pdo->errorInfo());         exit;      }   }   function delete($id){      $table_name = self::$table_name;      if(is_array($id)){         $id = implode(',', $id);      }      $sql = "delete from $table_name where id in ($id)";      $r = $this->pdo->exec($sql);      $this->getErrorInfo();      return $r;   }}function M($table_name){   $db = Db::getDb($table_name);   return $db;};$data = [   [      'name'=>'雪碧',      'class_name'=>'3333333',   ],   [      'name'=>'可樂',      'class_name'=>'3333333',   ],];$r = M('user')->delete(726);echo $r;