如何使用Php更新xml中的特定节点

Question

就像库存系统一样，如果我输入我要购买的商品数量，必须在（products.xml）上扣除，同时将订购的产品保存在（orders.xml）上。它在orders.xml上保存但股票没有更新。

股票被扣除但只能在输入框中看到，但未在＆＃34; products.xml＆＃34; 图片：The Ordering Form 图片：Xml File is not updating

<?php

$products =simplexml_load_file("product.xml") or die("ERROR");

foreach ($products->product as $product){
        if($product['id']==$_GET['id']){
            $id = $product['id'];
            $name =$product->name;
            $price = $product->price;
            $stocks = $product->stocks;

            break;
        }

    }


if(isset($_POST['submitSave'])){

    // $name = $_POST['name'];
    // $id = $_POST['id'];
    // $price = $_POST['price'];

    $quan = $_POST['quan'];

    $total = $price * $quan;

    $stocks = $stocks - $quan; // on minusing the stocks :<


    foreach ($products->product as $product){
        if($product['id']==$_POST['id']){
            // $product->name = $_POST['name'];
            // $product->price = $_POST['price'];
            $product->stocks = $_POST['stocks'];
            break;
        }

    }
    file_put_contents('product.xml',$products->asXML());




    $xml = new DOMDocument("1.0","UTF-8");
    $xml -> preserveWhiteSpace = TRUE;
    $xml -> formatOutput = true;





    if(file_exists("orders.xml")){
        $xml = simplexml_load_file('orders.xml');
        $order = $xml->addChild('order');
        $order->addChild('id', $id);
        $order->addChild('name', $name);
        $order->addChild('price', $price);
        $order->addChild('quan', $quan);

        $order->addChild('total', $total);


        $xml->saveXML("orders.xml");
        $xml=simplexml_load_file("orders.xml") or die("ERROR");
        $a=1;
        foreach($xml->children() as $order)
        {
        echo"<div class = 'orderlist' ";
        echo"<b>Order No.:". $a++."</b><br>";
        echo"Product Id: ".$order->id."<br>";
        echo"Product Name: ".$order->name."<br>";
        echo"Price: ".$order->price."<br>";
        echo"Quantity Ordered: ".$order->quan."<br>";
        echo"Total Price: ".$order->total."<br>";
        echo"</div><br>";
        }

    }
    else{
        $orders = $xml -> createElement("orders");
        $xml -> appendChild($orders);

        $order = $xml -> createElement("order");
        $orders -> appendChild($order);

        $id = $xml -> createElement("id", $id);
        $order -> appendChild($id);



        $name = $xml -> createElement("name", $name);
        $order -> appendChild($name);

        $price = $xml -> createElement("price", $price);
        $order -> appendChild($price);

        $quan = $xml -> createElement("quan", $quan);
        $order -> appendChild($quan);

        $total = $xml -> createElement("total", $total);
        $order -> appendChild($total);
        //echo "<xmp>" .$xml -> saveXML(). "</xmp>";
        file_put_contents("orders.xml", $xml->saveXML());

        // 



        $xml=simplexml_load_file("orders.xml") or die("ERROR");
        $a=1;
        foreach($xml->children() as $order)
        {
        echo"<div class = 'orderlist' ";

        echo"<b>.Order No.:".$a++."</b><br>";
        echo"Product Id: ".$order->id."<br>";
        echo"Product Name: ".$order->name."<br>";
        echo"Price: ".$order->price."<br>";
        echo"Quantity Ordered: ".$order->quan."<br>";
        echo"Total Price: ".$order->total."<br>";
        echo"</div><br>";
        }
    }
    // file_put_contents('product.xml',$products->asXML());
    // header('location: index.php');
}

?>
<form method="post">
<br><center>
    <table cellpadding="2" cellspacing="2">
        <tr>
            <td>Id</td>
            <td><input type="text" name="id" value="<?php echo $id;?>" ></td>
        </tr>
        <tr>
            <td>Name</td>
            <td><input type="text" name="name" value="<?php echo $name;?>" ></td>
        </tr>
        <tr>
            <td>Price</td>
            <td><input type="number" name="price" value="<?php echo $price;?>" ></td>
        </tr>
        <tr>
            <td>Stocks</td>
            <td><input type="number" name="stocks" value="<?php echo $stocks;?>"></td>
        </tr>

        <tr>
            <td>Quantity</td>
            <td><input type="number" name="quan" value="" ></td>
        </tr>

        <tr>
            <td>&nbsp;</td>
            <td><input type="submit" name="submitSave" value="Buy"></td>
        </tr>
    </table>