PHP session not set the first time - php

Question

I have an odd issue. The first time a visitor comes to the site and I set anything is the session, it doesn't stick. The second and all the following times I try to set something it sticks. After the initial try I can destroy the session and set something and it sticks. Its just the initial attempt to save something fails. I'm trying to save something to the session with $_SESSION['uid'] = $row["Id"];. I know the $row["Id"] is valid and holds data (I echoed it).
I am not using standard sessions. I am saving the session into a database. My session class is below. Is there anything I'm missing or doing wrong to explain this behavior?
Update:
Well I tested the session class on its own and it seems to be working :-/ But when I use it in my larger application _write never gets called, though __destruct does get called. Any idea why that may be?
<?php
include_once('db.php');
class PDOSession
{
protected $pdo;
protected $table = 'SessionData';
public function __construct()
{
// Get a database connection
$db = new PDOConnectionFactory();
$this->pdo = $db->getConnection(true);
// Start session
session_set_save_handler(array($this, '_open'),
array($this, '_close'),
array($this, '_read'),
array($this, '_write'),
array($this, '_destroy'),
array($this, '_gc'));
session_start();
}
public function __destruct()
{
session_write_close();
}
protected function fetchSession($id)
{
$stmt = $this->pdo->prepare('SELECT id, data FROM '.$this->table.' WHERE id = :id AND unixtime > :unixtime');
$stmt->execute(array(':id' => $id, ':unixtime' => (time() - (int)ini_get('session.gc_maxlifetime'))));
$sessions = $stmt->fetchAll();
return empty($sessions) ? false : $sessions[0];
}
public function _open($savePath, $sessionName)
{
return true;
}
public function _close()
{
return true;
}
public function _read($id)
{
$session = $this->fetchSession($id);
return ($session === false) ? false : $session['data'];
}
public function _write($id, $sessionData)
{
$session = $this->fetchSession($id);
if($session === false) {
$stmt = $this->pdo->prepare('INSERT INTO '.$this->table.' (id, data, unixtime) VALUES (:id, :data, :time)');
} else {
$stmt = $this->pdo->prepare('UPDATE '.$this->table.' SET data = :data, unixtime = :time WHERE id = :id');
}
$stmt->execute(array(
':id' => $id,
':data' => $sessionData,
':time' => time()
));
}
public function _destroy($id)
{
$stmt = $this->pdo->prepare('DELETE FROM '.$this->table.' WHERE id = :id');
$stmt->execute(array(':id' => $id));
}
public function _gc($maxlifetime)
{
$stmt = $this->pdo->prepare('DELETE FROM '.$this->table.' WHERE unixtime < :time');
$stmt->execute(array(':time' => (time() - (int) $maxlifetime)));
}
}
$newPDOSessionStartHere = new PDOSession();

Answer 1

I'm a bit of an idiot I guess. I was calling session_destroy() rather than session_unset() to clear things out at the top of my authentication script. The class works fine.

Answer 2

I think that you should start a session after you define your class. Not inside.