PHP Issue Updating Database On Button Click - php

Question

Hello I'm making a shop in php where I populate the shop with a while loop so all the shop items from my database are displayed. This works fine but I have an issue when I try to update the stock count and money left on the account when I press the buy button.
The $ItemCost variable only saves the last populated item cost and I'm not sure how to save the cost of each item to insert it into the database.
Also the $StockCount variable sets the stockcount to 1.
How can I fix this.
<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "useraccounts";
// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
$GatherItems = "SELECT * FROM shopitems WHERE StockCount > 0 ORDER BY`shopitems`.`Cost` DESC";
$result = $conn->query($GatherItems);
if ($result->num_rows > 0) {
// output data of each row
while($row = $result->fetch_assoc()) {
$ItemName = $row['ItemName'];
$ItemCost = $row['Cost'];
$ID = $row['ID'];
$StockCount = $row['StockCount'];
$Money = $row['Money'];
echo "<div class='test'>$ItemName</div>";
echo "<div class='test1'>$ItemCost </div>";
echo "<input type='submit' class='btn btn-primary' name='Buy' value='Buy Now'/>";
}
$NewTotal = $Money - $ItemCost;
$Inventory = "UPDATE shopitems SET StockCount = $StockCount-1, Money = $NewTotal WHERE ID = $ID";
if(isset($_POST['Buy'])){
if ($conn->query($Inventory) === TRUE) {
echo "New record created successfully";
} else {
echo "Error: " . $Inventory . "<br>" . $conn->error;
}
}
}
$conn->close();
?>

Answer 1

As #Sean said, you can do this like :
<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "useraccounts";
// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
if(isset($_POST['Buy'])){
// update stock and money
$ID = $_POST['ID'];
$Money = $_POST['Money'];
$ItemCost = $_POST['ItemCost'];
$NewTotal = $Money - $ItemCost;
$Inventory = "UPDATE shopitems SET StockCount = $StockCount-1, Money =
$NewTotal WHERE ID = $ID";
if ($conn->query($Inventory) === TRUE) {
echo "New record created successfully";
} else {
echo "Error: " . $Inventory . "<br>" . $conn->error;
}
}
// display items
$GatherItems = "SELECT * FROM shopitems WHERE StockCount > 0 ORDER
BY`shopitems`.`Cost` DESC";
$result = $conn->query($GatherItems);
if ($result->num_rows > 0) {
// output data of each row
while($row = $result->fetch_assoc()) {
$ItemName = $row['ItemName'];
$ItemCost = $row['Cost'];
$ID = $row['ID'];
$StockCount = $row['StockCount'];
$Money = $row['Money'];
echo "<form method='post' action=''>";
echo "<div class='test'>$ItemName</div>";
echo "<div class='test1'>$ItemCost </div>";
echo "<input type='hidden' name='Id' value='".$ID."'/>";
echo "<input type='hidden' name='Money' value='".$Money."'/>";
echo "<input type='hidden' name='ItemCost' value='".$ItemCost."'/>";
echo "<input type='submit' class='btn btn-primary' name='Buy' value='Buy Now'/>";
echo "</form>";
}
}
$conn->close();

Answer 2

Assuming you don't want ajax, and you don't want js, but only a 'buy' button under each item which will reopen the entire page, then you want something like this. This is pseudo code:
//FIRST we need to process the form:
<?php
if(isset($_POST['submit'])){
$itemId = $_POST['id'];
//do the stuff. Remember about escaping $itemId, or using prepared statements
//select... from where id = $itemId
}
?>
//now get the items:
<?php
$GatherItems = ...
?>
//now the html:
<?php
while($row = $result->fetch_assoc()) {
?>
<form method = 'post'>
<div class='test'><?=$ItemName?></div>
...
<input type = 'hidden' name = 'itemId' value = '<?=$ID?>'>
<input type = 'submit' name = 'submit' value = 'Buy'>
</form>
}
?>