如何使用PHP从XML获取标记的属性？

I have the following XML and code that I try to save it in mySQL. It is working but my problem is that I can not get the product id attribute.

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'product_id' cannot be null

<product id="1111845">
  <name><![CDATA[MadBiker 600]]></name>
  <link>http://demo.com/p.MadBiker-600.1111845.html</link>
  <price_with_vat>107.01</price_with_vat>
...
...
...
</product>

Here is the code

$xml = simplexml_load_file("demo.xml");

   foreach($xml->products->product as $data) {
        $sql = "INSERT INTO products (shop, product_id, name, price, shipping, manufacturer, stock, availability)
            VALUES (:SHOP, :ID, :NAME, :PRICE, :SHIPPING, :MANUFACTURER, :STOCK, :AVAILABILITY)";
        $stmt = $dbh->prepare($sql);

            "ID" => $data->product[id] ,
            "NAME" => $data->name,
            "PRICE" => $data->price_with_vat,

How to do this?

Your foreach loop iterates over <product> nodes already:

foreach ($xml->products->product as $data) {
  //...
}

So in this case, $data already represents <product> and you don't want to use $data->product. Then it is just a matter of referencing the ['id'] attribute by array key on $data itself so:

"ID" => (string)$data['id']

(Don't forget to cast it to a string - and the other nodes will need the same treatment via (string))

"NAME" => (string)$data->name,
"PRICE" => (string)$data->price_with_vat,

The fact that PHP didn't show other warnings suggests you don't have display_errors on. Always when developing code, use

error_reporting(E_ALL);
ini_set('display_errors', 1);

Or set them in php.ini.

Instead of using

$data->product['id'], 
$data->name,
$data->price_with_vat,

use

$data['product'][0]
$data['name']
$data['price_with_vat']

http://php.net/manual/en/simplexmlelement.attributes.php

Try (int)$data->product['id'], you need to cast attributes when using SimpleXML.