PHP 7 - IF statements doesn't seem to work while trying to detect KEYS in $_SESSION arrays

Question

[PHP 7.1]

Below you can see my PHP code. My problem comes from my difficult to understand why the second IF statement doesn't work with the array $_SESSION['items'], but does work with the testing array $zoo (I just created $zoo to make tests in place of $_SESSION['items']).

I've an AJAX script that send POST data to the PHP code and then logs the response to the browser console in order to let me review the results. Everything was working fine with my tests, all changes done to other arrays where executed with fine results, the only issue I couldn't understand and solve, even after extensively searching for some clues on the web and trying different things, is the misterious ways of the $_SESSION array that doesn't seem to like to expose its keys to lurking IF statements... And I got here trying to detect the existence of a key inside an array in order to increment its value. Something I already did before with other arrays that weren't $_SESSION arrays and it worked just fine.

session_start();

$_SESSION['items'] = array();
$zoo['animals'] = array('tiger'=>2,'lion'=>3);

if(isset($_POST['item_name'])) {
    if (isset($_SESSION['items'][$_POST['item_name']]) || array_key_exists($_POST['item_name'], $_SESSION['items'])) {
        $_SESSION['items'][$_POST['item_name']]['qnt']++;

    } else {
        $_SESSION['item_name'][$_POST['item_name']] = array('model'=>$_POST['item_model'], 'qnt'=>1);

    }

    echo json_encode($_SESSION['items']);

    exit();
  }

Answer 1

This is a simplified version of your code with just the important stuff

 session_start();

 $_SESSION['items'] = array(); //items is now emtpy

 if (isset($_SESSION['items'][$_POST['item_name']]) || array_key_exists($_POST['item_name'], $_SESSION['items'])) {

 }

This should make it a bit easier to see, so it's simply because items is an empty array. Do to assigning it as such before the condition.

To fix it, either remove this line:

$_SESSION['items'] = array();

OR better yet:

$_SESSION['items'] = isset($_SESSION['items']) ? $_SESSION['items'] : [];

OR even

if(!isset($_SESSION['items'])) $_SESSION['items'] = [];

It's up to you how you fix it, but I am certain you don't want to reset that to an empty array. It's a very easy mistake to make, and a hard one to find because it's technically legal PHP code. I just have a built in debugger in my head now, from years of coding ... lol ... Most times I can literally picture in my mind how something will execute.

Cheers!