PHP 中的 PostgreSQL - 会话变量似乎在发布数据时自行取消设置

Question

I'm trying to handle a form that updates some data in a postgreSQL table. To do that, I GET the id for the item to update. The URL reads:

[...]pojazd.php?id=1[...] , which successfully GETs the data.

Then I want to store it in a session (that was opened before):

$_SESSION['id'] = $_GET['id'];
$id = $_SESSION['id']; 

When I use my $id variable to SELECT the data, it works fine.

SELECT model, cena FROM pojazd WHERE id_poj = $id" does the job.

But when I want to update this data using a POST form:

if (isset($_POST['update'])){
[...]
UPDATE pojazd SET model = '$model', cena = '$cena' WHERE id_poj = $id;
}

nothing happens. When the $id variable is hardcoded (for example: replaced by 1 etc), it works fine. But the $id variable seems to unset itself whenever the form is POSTed. I tried echo'ing the $id variable whilst disabling the redirecting, and that's exactly what happens - the $id variable disappears.

I'm at a loss. The clock is ticking, I really don't want to fail my class, but that problems ruins my entire project...

Answer 1

You need to replace

$_SESSION['id'] = $_GET['id'];

with

if (isset($_GET['id'])) $_SESSION['id'] = $_GET['id'];

so that the value doesn't get overwritten with an empty value when the form is POST ed...