<?php
/** create XML file */ 
$mysqli = new mysqli("localhost", "root", "", "dbbookstore");
/* check connection */
if ($mysqli->connect_errno) {
   echo "Connect failed ".$mysqli->connect_error;
   exit();
}
$query = "SELECT id, title, author_name, price, ISBN, category FROM books";
$booksArray = array();
if ($result = $mysqli->query($query)) {
    /* fetch associative array */
    while ($row = $result->fetch_assoc()) {
       array_push($booksArray, $row);
    }
  
    if(count($booksArray)){
         createXMLfile($booksArray);
     }
    /* free result set */
    $result->free();
}
/* close connection */
$mysqli->close();
function createXMLfile($booksArray){
  
   $filePath = 'book.xml';
   $dom     = new DOMDocument('1.0', 'utf-8'); 
   $root      = $dom->createElement('books'); 
   for($i=0; $i<count($booksArray); $i++){
     
     $bookId        =  $booksArray[$i]['id'];  
     $bookName = htmlspecialchars($booksArray[$i]['title']);
     $bookAuthor    =  $booksArray[$i]['author_name']; 
     $bookPrice     =  $booksArray[$i]['price']; 
     $bookISBN      =  $booksArray[$i]['ISBN']; 
     $bookCategory  =  $booksArray[$i]['category'];  
     $book = $dom->createElement('book');
     $book->setAttribute('id', $bookId);
     $name     = $dom->createElement('title', $bookName); 
     $book->appendChild($name); 
     $author   = $dom->createElement('author', $bookAuthor); 
     $book->appendChild($author); 
     $price    = $dom->createElement('price', $bookPrice); 
     $book->appendChild($price); 
     $isbn     = $dom->createElement('ISBN', $bookISBN); 
     $book->appendChild($isbn); 
     
     $category = $dom->createElement('category', $bookCategory); 
     $book->appendChild($category);
 
     $root->appendChild($book);
   }
   $dom->appendChild($root); 
   $dom->save($filePath); 
 }