PDO包装器返回NULL

Question

I have the following PDO Initialization set in my constructor for a PDO wrapper:

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);      
}

My main problem is that when I set dbh to initialize as a parent in a constructor, it returns NULL .

and that creates a chain reaction.

Is there anything specific that I'm doing wrong?

Answer 1

You don't understand the parent::__construct() call.

Calling parent::__construct() doesn't return anything:

<?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
}

?>

Calling parent::__construct() simply calls the parent constructor on your object. Any variables defined in the parent will be set, etc. It doesn't return anything.

Answer 2

You are mixing up wrapping a class and inheriting a class.

Either do this (wrapping):

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

}

Or (inheriting):

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

}