PHP submitting a form is destroying my sessions - php

Question

Hello I am trying to make a form in the page where I created a session so when I submit the form the sessions gets destroyed here is my code:
<form method="post">
<h5>Name</h5>
<input type=text name="name" class="insertname">
<br>
<br>
<input type="submit" name="namesearch" class="insertbutton"></input>
</form>';
PHP code to start the session :
<?php
if(isset($_POST['s']))
{
$a=$_POST['uid']; //accessing value from the text field
$enteredpass = $_POST['pwd']; //accessing value from the text field
$client = new MongoDB\Client('xxxx');
$companydb = $client->test;
$jsons = $companydb->jsons;
$ownerid = $jsons->findOne(
['ID' => $a]
);
$idcoded = $ownerid->ID;
if (empty($idcoded)) {
echo "<h1>empty</h1>";
}
if (!empty($idcoded)) {
$passcoded = $ownerid->pass;
if ($passcoded == $enteredpass) {
session_start();
}
}
}
?>

Answer 1

Make sure you have session_start(); at the top of all the PHP scripts
So, put the session_start(); at the top of the script and set say $_SESSION["uid"] when the user has correctly entered the credentials
A normal practice is to set $_SESSION["uid"]=""; (set initial value) before the user logs in the system, and then use this session variable to determine whether the user has successfully logged in.
So
<?php
session_start();
if(isset($_POST['s']))
{
$a=$_POST['uid']; //accessing value from the text field
$enteredpass = $_POST['pwd']; //accessing value from the text field
$client = new MongoDB\Client('xxxx');
$companydb = $client->test;
$jsons = $companydb->jsons;
$ownerid = $jsons->findOne(
['ID' => $a]
);
$idcoded = $ownerid->ID;
if (empty($idcoded)) {
echo "<h1>empty</h1>";
}
if (!empty($idcoded)) {
$passcoded = $ownerid->pass;
if ($passcoded == $enteredpass) {
$_SESSION["uid"]=$_POST['uid'];
} else {
$_SESSION["uid"]="";
}
}
}
?>