how to add an id to $_SERVER["PHP_SELF"] submit - php

Question

I am wanting to submit a form using $_SERVER["PHP_SELF"]however its not picking up the id of the item when the form is being submitted, is there a way to add an id like the following and not have to link to another file...
<form action="process.php<?php echo"?id=$productID" ?> " method="post">
Surely there is a simple way of doing this.. I have spent alot of time googling and searching forums and nothing is giving me an explanation.
Thanks in advance.
EDIT
include "../model/functions_updateproducts.php";
function select_productspreparedGETIDt(){
global $conn;
$productID = $_GET['id'];
$nameError = "";
$sql = "SELECT * FROM product WHERE productID = :productID";
$statement = $conn->prepare($sql);
$statement->bindValue(':productID', $productID);
$statement->execute();
$result = $statement->fetchAll();
$statement->closeCursor();
foreach($result as $row):
?>
<form action="<?php echo $_SERVER["PHP_SELF"];?>" method="post">
<div class="form-group">
<input type="hidden" id="productID" name="productID" value="<?php echo $row['productID'] ?>" />
<label>Product Name</label>
<input type="text" class="form-control" id="productName" name="productName" placeholder="Enter Product Name" value="<?php echo $row['productName'] ?>" /><span class="error"> <?php echo $nameError;?></span>
</div>
<div class="form-group">
<label>Quantity</label>
<input type="Number" class="form-control" id="QTY" name="QTY" placeholder="Enter Quantity" value="<?php echo $row['QTY'] ?>" min='1' max='100' >
</div>
<div class="form-group">
<label>Price</label>
<input type="text" class="form-control" id="productPrice" name="productPrice" placeholder="Enter Price" value="<?php echo $row['productPrice'] ?>" required/>
</div>
<div class="form-group">
<label>Variable</label>
<input type="text" class="form-control" id="Variable" name="Variable" placeholder="Enter Variable" value="<?php echo $row['Variable'] ?>" required>
</div>
<div class="form-group">
<label>Description</label>
<textarea class="form-control" id="productDescription" name="productDescription" /><?php echo $row['productDescription'] ?></textarea>
</div>
<button type="submit" class="btn btn-primary">Update Item</button>
</form>
<?php
endforeach;
}
$nameError ="";
if(isset($_POST['submit'])){
if (empty($_POST["productName"])) {
$nameError = "Name is required";
} else {
$name = test_input($_POST["productName"]);
// check name only contains letters and whitespace
if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
$nameError = "Only letters and white space allowed";
}
}
$productID = $_GET['id'];
$productName = $_POST['productName'];
$productDescription = $_POST['productDescription'];
$productPrice = $_POST['productPrice'];
$QTY = $_POST['QTY'];
$Variable = $_POST['Variable'];
global $conn;
$sql = "UPDATE product SET productName = :productName, productDescription = :productDescription, productPrice = :productPrice, QTY = :QTY, Variable = :Variable WHERE productID = :productID";
$statement = $conn->prepare($sql);
$statement->bindValue(':productName', $productName);
$statement->bindValue(':productDescription', $productDescription);
$statement->bindValue(':productPrice', $productPrice);
$statement->bindValue(':productID', $productID);
$statement->bindValue(':QTY', $QTY);
$statement->bindValue(':Variable', $Variable);
$result = $statement->execute();
$statement->closeCursor();
header("location: ../view/success.php");
return $result;
function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
?>
<?php
}
?>

Answer 1

Inside your form put this code:
<input type="hidden" value="<?php echo $productID ?>" name="id" />
This will submit the hidden field. PHP wrote your $productID to it and it get submitted as part of the $_POST[]

Answer 2

<form action="process.php<?php echo"?id=$productID" ?> " method="post">
is totally fine.. access the productID with
$_GET['id']