PDO类扩展时对象声明中的错误 [英] Error in object declaration when PDO class is extended

问题描述

我创建了三个类。一个类是从PDO扩展的db。其他两个类从db类继承。但问题是当我初始化这些子类的对象时，第二个对象被创建为第一个对象的克隆。感谢您提供任何帮助。

I have create three classes. One class is db which extends from PDO. Other two class extends from the db class. But the problem is when I initialize objects of these sub classes the second object is created as clone of the first object. Thanks in advance for any help.

<?php
/** The Database Driver */
define('DB_DRIVER', 'mysql');

/** The name of the database */
define('DB_NAME', 'sample');

/** MySQL database username */
define('DB_USER', 'root');

/** MySQL database password */
define('DB_PASSWORD', 'root');

/** MySQL hostname */
define('DB_HOST', 'localhost');

class db extends PDO
{
    public function __construct()
    {
        echo "DB constructor called\n";
        $options = array(
            PDO::ATTR_PERSISTENT => true,
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
        );
        $dsn = DB_DRIVER . ":host=" . DB_HOST . ";dbname=" . DB_NAME;
        parent::__construct($dsn, DB_USER, DB_PASSWORD, $options);
    }
}

class Admin extends db
{
    private $uid, $username, $password, $level, $name, $email;

    public function __construct()
    {
        echo "Admin constructor called\n";
        parent::__construct();
    }
}

class Movie extends db
{
    private $mid, $title, $slug;

    public function __construct()
    {
        echo "Movie constructor called\n";
        parent::__construct();
    }
}


$adminObj = new Admin();
$movieObj = new Movie();
var_dump($adminObj);
var_dump($movieObj);
?>

---

这是上面的输出。 请注意输出中显示的对象类型

---

Here is the output of the above. Please note the type of objects shown in the output.

Admin constructor called
DB constructor called
Movie constructor called
DB constructor called
object(Admin)#1 (6) {
  ["uid":"Admin":private]=>
  NULL
  ["username":"Admin":private]=>
  NULL
  ["password":"Admin":private]=>
  NULL
  ["level":"Admin":private]=>
  NULL
  ["name":"Admin":private]=>
  NULL
  ["email":"Admin":private]=>
  NULL
}
object(Admin)#2 (6) {
  ["uid":"Admin":private]=>
  NULL
  ["username":"Admin":private]=>
  NULL
  ["password":"Admin":private]=>
  NULL
  ["level":"Admin":private]=>
  NULL
  ["name":"Admin":private]=>
  NULL
  ["email":"Admin":private]=>
  NULL

}

当父:: __结构（$ dsn，DB_USER，DB_PASSWORD，$ options）;

When the parent::__construct($dsn, DB_USER, DB_PASSWORD, $options); in the db class is removed the issue will disappear.

推荐答案

您有 PDO :: ATTR_PERSISTENT => ; true，，并且您正在尝试使用相同的DSN字符串创建2个PDO对象。这会告诉PDO在您 $ movieObj = new Movie（）; 而不是创建新连接时返回已建立的连接。

You have PDO::ATTR_PERSISTENT => true, and you are attempting to create 2 PDO objects with the same DSN string. This tells PDO to return already established connection when you do $movieObj = new Movie(); instead of creating new one.

您的案例中的解决方案：
PDO :: ATTR_PERSISTENT => false，

Solution in your case: PDO::ATTR_PERSISTENT => false,

有用的链接：连接和连接管理

当父:: __结构（$ dsn，
DB_USER，DB_PASSWORD，$ options）;在
中，db类被删除，
消失。
是，因为在这种情况下不会创建实际的PDO对象。

When the parent::__construct($dsn, DB_USER, DB_PASSWORD, $options); in the db class is removed the issue will disappear. Yes, because the actual PDO object will not be created in this case.

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