wierd behaviour of unset php - php

Question

I am developing an e-commerce website on which i need to store sessions inside database.I did that by implementing SessionHandlerInterface Class that is provided by the php itself.However it works totally fine and did store sessions inside the database , as well as read them properly.
However I am facing problem when I am using unset to unset a session variable.Sometimes it does work.Sometimes it doesn't.
For example:If i have a session variable by the name ABC unset might delete it from the database or it doesn't deletes the variable.
<?php
//inc.session.php
require_once 'RemoteAddress.php';
class SysSession implements SessionHandlerInterface
{
private $remote_write;
private $remote_read;
private $link;
private $ip_address_write;
private $ip_address_read;
public function open($savePath, $sessionName)
{
$link = new mysqli("localhost","root","","cakenbake");
if($link){
$this->link = $link;
return true;
}else{
return false;
}
}
public function close()
{
mysqli_close($this->link);
return true;
}
public function read($id)
{
$this->remote_read=new RemoteAddress();
$this->ip_address_read=$this->remote_read->getIpAddress();
$stmt=$this->link->prepare("SELECT `Session_Data`,`ip_address` FROM Session WHERE `Session_Id` = ? AND `Session_Expires` > '".date('Y-m-d H:i:s')."'");
$stmt->bind_param("s",$id);
$stmt->execute();
//$result = mysqli_query($this->link,"SELECT Session_Data FROM Session WHERE Session_Id = '".$id."' AND Session_Expires > '".date('Y-m-d H:i:s')."'");
/*$result=$this->link->prepare("Some query inside")
* This shows up an error stating prepare method not found
*
*/
$res=$stmt->get_result();
if($row=$res->fetch_assoc()){
if($this->ip_address_read==$row['ip_address'])
return $row['Session_Data'];
else return "";
}else{
return "";
}
}
public function write($id, $data)
{
$this->remote_write=new RemoteAddress();
$this->ip_address_write=$this->remote_write->getIpAddress();
if(!empty($data))
{
$DateTime = date('Y-m-d H:i:s');
$NewDateTime = date('Y-m-d H:i:s',strtotime($DateTime.' + 1 hour'));
$stmt=$this->link->prepare("REPLACE INTO Session SET Session_Id = ?, Session_Expires = '".$NewDateTime."', Session_Data = '".$data."', ip_address = '".$this->ip_address_write."'");
$stmt->bind_param("s",$id);
// $result = mysqli_query($this->link,"REPLACE INTO Session SET Session_Id = '".$id."', Session_Expires = '".$NewDateTime."', Session_Data = '".$data."'");
if($stmt->execute()){
return true;
}else{
return false;
}
}
}
public function destroy($id)
{
$stmt = $this->link->prepare("DELETE FROM Session WHERE Session_Id =?");
$stmt->bind_param("s",$id);
if($stmt->execute()){
return true;
}else{
return false;
}
}
public function gc($maxlifetime)
{
$result = $this->link->query("DELETE FROM Session WHERE ((UNIX_TIMESTAMP(Session_Expires) + ".$maxlifetime.") < UNIX_TIMESTAMP(NOW()))");
if($result){
return true;
}else{
return false;
}
}
}
$handler = new SysSession();
session_set_save_handler($handler, true);
?>
The above code stores and read sessions from the database.
Structure of the session table.
What could be the possible reason for this weird behaviour. Do i have to implement unset function as well?.
How should i resolve this problem?
If you could suggest me someother already written code for storing in database.That would work as well but i dont need any frameworks such as codeigniter and Yii2.
If you need more information regarding this problem.I will update my question.
Thanks in advance!

Answer 1

The problem is not with the unset function but with your write function.The write function is responsible for any updates that are made to the specific session id.
The wierd behiviour is not with the unset but it is with the write funciton you have implemented.
See ,the !empty constraint checks if your data is empty or not.What i can guess is that your database for that specific id must be empty after the removal of the specific variable .So the write tries to update your row with an empty value but with that constraint it isn't able to do so.
Just remove the !empty tag and it will work like a charm.