Question

我在构造函数中为PDO包装器设置了以下PDO初始化：

public function __construct($engine, $host, $username, $password, $dbName)
{
    $this->host = $host;
    $this->dsn = $engine.':dbname='.$dbName.';host='.$host;
    $this->dbh = parent::__construct($this->dsn, $username, $password);
    $this->dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);      
}

我的主要问题是当我将dbh设置为在构造函数中初始化为父类时，它返回NULL。

这会产生连锁反应。

有什么具体的我做错了吗？

Answer 1

您不理解parent::__construct()来电。

调用parent::__construct()不会返回任何内容：

<?php

class Obj {

   public  $deja;

   public function __construct() {
      $this->deja = "Constructed";
   }

}

$obj = new Obj();


class eObj extends Obj {


   public $parent;

   public function __construct() {
      $this->parent = parent::__construct();
   }

}

$eObj = new eObj();

if($eObj->parent==null) {
    echo "I'm null";
    echo $eObj->deja; // outputs Constructed
}

?>

调用parent::__construct()只是调用对象上的父构造函数。将设置父级中定义的任何变量，等等。它不会返回任何内容。

Answer 2

你正在混合包装一个类并继承一个类。

要么这样做（包装）：

class YourDB
{
    public function __construct($engine, $host, $username, $password, $dbName)
    {
        $this->host = $host;
        $this->dsn = $engine.':dbname='.$dbName.';host='.$host;
        // here we are wrapping a PDO instance;
        $this->dbh = new PDO($this->dsn, $username, $password);
        $this->dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);      
    }

    // possibly create proxy methods to the wrapped PDO object methods

}

或（继承）：

class YourDB
    extends PDO // extending PDO, and thus inheriting from it
{
    public function __construct($engine, $host, $username, $password, $dbName)
    {
        $this->host = $host;
        $this->dsn = $engine.':dbname='.$dbName.';host='.$host;
        // here we are calling the constructor of our inherited class
        parent::_construct($this->dsn, $username, $password);
        $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);      
    }

    // possibly override inherited PDO methods

}

PDO Wrapper返回NULL

2 个答案: