PDO致命错误 - 调用一个非对象的成员函数prepare（）

Question

此代码出错。

Fatal error: Call to a member function prepare() on a non-object in C:\wamp\www\progapps\addReminder.php on line 12

这里是我的代码：

addReminder.php

<?php 

include_once("includes/database.php"); 

try { 
    global $dbh; 
    $query = $dbh -> prepare("SELECT * FROM reminder_type;"); 
    $query->setFetchMode(PDO::FETCH_ASSOC); 
    $query ->execute(); 
} catch(PDOException $ex) { 
    echo $ex->getMessage(); 
} 

?> 

这是数据库的连接。

database.php中

<?php 

    include("constants.php"); 

    class MySQLDB { 

     function MySQLDB(){ 
      global $dbh; 
      try{  
       $dbh = new PDO('mysql:host='.DB_SERVER.';dbname='.DB_NAME.'',DB_USER,DB_PASS); 
       $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
       $dbh->setAttribute(PDO::ATTR_CASE, PDO::CASE_LOWER); 
      }catch(PDOException $e){ 
       echo $e->getMessage(); 
       die(); 
      } 
     } 
    } 

这里是常数

constants.php

<?php 
$currency = '&#x20b1;'; 
define("DB_SERVER", "localhost"); 
define("DB_USER", "root"); 
define("DB_PASS", ""); 
define("DB_NAME", "hrisdb"); 
?> 

什么是可能的原因是什么？我该如何解决这个问题？感谢你们！

Answer 1

这应该工作

$currency = '₱'; 
define("DB_SERVER", "localhost"); 
define("DB_USER", "root"); 
define("DB_PASS", ""); 
define("DB_NAME", "hrisdb"); 



try { 
    $dbh = new PDO('mysql:host=' . DB_SERVER . ';dbname=' . DB_NAME . '', DB_USER, DB_PASS); 
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
    $dbh->setAttribute(PDO::ATTR_CASE, PDO::CASE_LOWER); 
} catch (PDOException $e) { 
    echo $e->getMessage(); 
    die(); 
} 




try { 

    $query = $dbh->prepare("SELECT * FROM reminder_type;"); 
    $query->setFetchMode(PDO::FETCH_ASSOC); 
    $query->execute(); 
} catch (PDOException $ex) { 
    echo $ex->getMessage(); 
} 

，如果你想成为一个类里面看看这12 extending PDO class

Answer 2

您还没有调用函数MySQLDB。所以变量$dbh甚至不存在。