使用php将XML文件按升序排序 - Sorting XML File into ascending order using php

我有一个xml文件，其中包含大约60本书，我需要使用php将这些书从borrowedcount按升序排列，到目前为止，我的代码显示了所有的书，但不会排序？任何帮助都会被告知

PHP

<?php

$xmlassignDoc = new DOMDocument();
$xmlassignDoc->load("books.xml");

$books = $xmlBookDoc->getElementsByTagName("item");
foreach($books as $list)
{
    $course = $list->getElementsByTagName("course");
    $course = $course->item(0)->nodeValue;

//HERE is where the GET function will be
    if ($course == "CC150")
    {
    print_r($array);
        $id = $list->getAttribute("id");
        echo "<b>Book ID: </b> $id <br>";
         $title = $list->getElementsByTagName("title");
         $title = $title->item(0)->nodeValue;
         echo "<b>Title: </b> $title <br>";
         $isbn = $list->getElementsByTagName("isbn");
         $isbn = $isbn->item(0)->nodeValue;
         echo "<b>ISBN: </b> $isbn <br>";
         $borrowed = $list->getElementsByTagName("borrowedcount");
         $borrowed = $borrowed->item(0)->nodeValue;
         echo "<b>Borrowed Count: </b> $borrowed <br>";
         echo "<br>";
    } 
}
//print $xmlBookDoc->saveXML();
?>

xml文件

<?xml version="1.0" encoding="utf-8"?>
<bookcollection>
<items>
  <item id="51390">
     <title>Management of systems development /</title>
     <isbn>0091653215</isbn>
     <url>http://library.hud.ac.uk/catlink/bib/51390</url>
     <borrowedcount>45</borrowedcount>
     <courses>
        <course>CC140</course>
        <course>CC210</course>
     </courses>
  </item>
  <item id="483">
     <title>Database systems management and design /</title>
     <isbn>0877091153</isbn>
     <url>http://library.hud.ac.uk/catlink/bib/483</url>
     <borrowedcount>28</borrowedcount>
     <courses>
        <course>CC140</course>
     </courses>
  </item>
  <item id="585842">
     <title>E-learning skills /</title>
     <isbn>0230573126</isbn>
     <url>http://library.hud.ac.uk/catlink/bib/585842</url>
     <borrowedcount>5</borrowedcount>
     <courses>
        <course>CC157</course>
     </courses>
  </item>

我的解决方案：

$books = array();
$xml = simplexml_load_file('books.xml'); 
foreach($xml->items->item as $item) {
    $books[] = array(
                     'id'             => (string)$item->attributes()->id,
                     'title'          => (string)$item->title,
                     'isbn'           => (string)$item->isbn,
                     'course'         => (string)$item->courses->course[0],
                     'borrowed_count' => intval($item->borrowedcount)
                    );
}

array_sort_by_column($books, 'borrowed_count');
var_dump($books);

以及分拣功能：

function array_sort_by_column(&$array, $column, $direction = SORT_ASC) {
    $reference_array = array();
    foreach($array as $key => $row) {
        $reference_array[$key] = $row[$column];
    }
    array_multisort($reference_array, $direction, $array);
}

文件"1.php"：

<?php
include 'books.php';
$b=new books();
$arr=$b->load('books.xml');         //1. load books from xml to array
usort($arr, array('books','cmp'));  //2. sort array
$b->save('out.xml',$arr);           //3. save array to xml
?>

文件"books.php"：

<?php
  class books
  {
     //load books from xml to array
     public function load($fname)
     {
        $doc=new DOMDocument();
        if($doc->load($fname))  $res=$this->parse($doc);
        else                    throw new Exception('error load XML');
        return $res;
     }

     static public function cmp($a, $b)
     {
         if ($a['fields']['borrowedcount'] == $b['fields']['borrowedcount']) {
             return 0;
         }
         return ($a['fields']['borrowedcount'] < $b['fields']['borrowedcount']) ? -1 : 1;
     }

     private function parse($doc)
     {
        $xpath = new DOMXpath($doc);
        $items = $xpath->query("items/item");
        $result = array();
        foreach($items as $item)
        {
           $result[]=array('id'=>$item->getAttribute('id'), 'fields'=>$this->parse_fields($item));
        }
        return $result;
     }

     private function parse_fields($node)
     {
        $res=array();
        foreach($node->childNodes as $child)
        {
           if($child->nodeType==XML_ELEMENT_NODE)
           {
              $res[$child->nodeName]=$this->get_value($child);
           }
        }
        return $res;
     }
     private function get_value($node)
     {
        if($node->nodeName=='courses')
        { 
           $res=array();
           foreach($node->childNodes as $child)
           {
              if($child->nodeType==XML_ELEMENT_NODE)
              {
                 $res[]=$child->nodeValue;
              }
           } 
           return $res;
        }
        else
        {
           return $node->nodeValue;
        }
     }
     //save array to xml
     public function save($fname, $rows)
     {
        $doc = new DOMDocument('1.0','utf-8');
        $doc->formatOutput = true;
        $bc = $doc->appendChild($doc->createElement('bookcollection'));
        $items = $bc->appendChild($doc->createElement('items'));
        foreach($rows as $row)
        {
           $item=$items->appendChild($doc->createElement('item'));
           $item->setAttribute('id',$row['id']);
           foreach($row['fields'] as $field_name=>$field_value)
           {
              $f=$item->appendChild($doc->createElement($field_name));
              if($field_name=='courses')
              {
                 foreach($field_value as $course_val)
                 {
                    $course=$f->appendChild($doc->createElement('course'));
                    $course->appendChild($doc->createTextNode($course_val));
                 }
              }
              else
              {
                 $f->appendChild($doc->createTextNode($field_value));
              }
           }
        }
        file_put_contents($fname, $doc->saveXML());
     }
  }
?>