Question

I instantiated a PDO object instead of a mysqli object in my database class. Obviously my mysqli functions no longer work. How do I update this line.

$row=mysqli_fetch_row(database::query($query));    

one_db::$db holds the pdo resource…query is just…

public function query($query) 
{
    return one_db::$db->query($query);
}

Actually I’m not sure if this needs updating as well to work with PDO…

Here is my PDO instantiation, I left in the mysqli for comparison

private function __construct() 
{
    self::create_pdo_object();
}

private function create_pdo_object()
{
    try {
        self::$db = new PDO(DB_DRIVER, DB_USER, DB_PASS);
    } catch (PDOException $e) {
        echo 'Connection failed: ' . $e->getMessage();
    }
}

private function create_mysqli_object()
{
    self::$db=new mysqli(DB_HOST, DB_USER, DB_PASS, DB_DATABASE);   
}

Answer 1

It looks like you might ought to consider using the factory pattern. Unfortunately, in your case, I don’t want to rewrite your entire class so we’re gonna use a modified factory pattern. Create a function named factory() like so:

public static function factory($type = 'mysqli')
{
    switch ($type) {
        case 'pdo':
            return self::create_pdo_object();
        case 'mysqli':
        default:
            return self::create_mysqli_object();
    }
}

Incidentally, if you’re going to use self then your functions should be declared static. In which case, it’s considered best practice to prefix them with underscores. And if you’re gonna go that route, then you might as well follow the convention for camel casing function names. (although, it could be argued that those functions should be public in case you don’t want to use factory, in which case you should omit the underscore prefix).

Also, your __construct() function should have the public access modifier. You could call factory() from within your constructor, but they are static methods using a static class member (self::$db), so instantiating an object is kind of pointless. Nevertheless, here is the code:

public function __construct($type = 'mysqli') 
{
    self::factory($type);
}

public static function factory($type = 'mysqli')
{
    switch ($type) {
        case 'pdo':
            // return self::createPdoObject();
            // or, if private  
            return self::_createPdoObject();
        case 'mysqli':
        default:
            // return self::createMysqliObject();
            // or, if private  
            return self::_createMysqliObject();
    }
}

// public static function createPdoObject()
// or
private static function _createPdoObject()
{
    try {
        self::$db = new PDO(DB_DRIVER, DB_USER, DB_PASS);
    } catch (PDOException $e) {
        echo 'Connection failed: ' . $e->getMessage();
    }
}

// public static function createMysqliObject()
// or
private static function _createMysqliObject()
{
    self::$db = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_DATABASE);   
}

As far as fetching a row with PDO, you would need to alter the code to something like:

if ($db instanceof PDO) {
    $query = $db->prepare($sqlSelectString);
    $query->execute();

    // or use PDO::FETCH_ASSOC if you want arrays instead
    $result = $query->fetch(PDO::FETCH_OBJ);
}

If this code exists in your db class, then you would change $db to self::$db, but I’m not sure where you would want to put that code..

For more information on querying using PDO, check out this page.