使用C＃检查XML中是否存在元素

Question

Why do I get false value for hasIdentifier variable, when I see in i-th document anything_start_i.xml that there is <identifier>value</identifier> element.

XDocument doc = XDocument.Load(args[0] + "/?verb=GetRecord&metadataPrefix=p3dm&identifier=" + i);
doc.Save("anything_start" + i + ".xml");
bool hasIdentifier = doc.Elements("identifier").Any();
Console.WriteLine(hasIdentifier);

Tried with Descendants instead of Elements, and again false.

XML:

<?xml version="1.0" encoding="utf-8"?>
    <OAI-PMH xmlns="..." xmlns:xsi="..." xsi:schemaLocation="...">
      <responseDate>...</responseDate>
      <request verb="GetRecord" identifier="1"</request>
      <GetRecord>
        <record>
          <header>
            <identifier>1</identifier>
            <datestamp>...</datestamp>
          </header>
          <metadata>
            <P3DM xmlns="..." xsi:schemaLocation="...">
              <MODELINFOID>1</MODELINFOID>
              <TITLE>Roth</TITLE>
  ....

Well, I would like to save all documents, and trying to stop saving when there is no documents any more (actually there is but without meaningful data). So, this is how i started:

static void Main(string[] args)
{
  var i = 1;
  bool work = true;
  do{
    XDocument doc = XDocument.Load(args[0] + "/?verb=GetRecord&metadataPrefix=p3dm&identifier=" + i);
    bool hasIdentifier = doc.Elements("identifier").Any();
    if (hasIdentifier) {
        doc.Save("anything" + i + ".xml");
        i++;
     }else{ 
        work = false;
     }
  } while (work);

Answer 1

XNamespace ns = "you namespace goes here";
bool hasIdentifier = doc.Descendants(ns + "identifier").Any();