Question

I am trying to compose an algorithm that will take XML as input, and find a value associated with a particular element, but the position of the element within the XML body varies. I have seen many examples of using XDocument.Descendants() but most (if not all) the examples expect the structure to be consistent, and descendants well known. I presume I will need to recurse the XML to find this value, but before heading that way, ask the general population.

What is the best way to find an element in an XDocument when the path for the element may be different on each call? Just need the first occurrence found, not in any particular order. Can be first occurrence found by going wide, or by going deep.

For example, if I am trying to find the element “FirstName”, and if the input XML for Call one looks like..

<?xml version="1.0"?>
<PERSON><Name><FirstName>BOB</FirstName></Name></PERSON>

and the next call looks like:

<?xml version="1.0"?>
<PERSONS><PERSON><Name><FirstName>BOB</FirstName></Name></PERSON></PERSONS>

What do you recommend? Is there a “Find” option in XDocument that I have not seen?

UPDATE:

Simple example above works with lazyberezovsky answer of XDocument.Descendents, but real XML does not. My problematic XML…

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Header>
    <To s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/addressing/none">http://localhost:52087/Service1.svc</To>
    <Action s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/addressing/none">http://tempuri.org/IService1/GetDataUsingDataContract</Action>
  </s:Header>
  <s:Body>
    <GetDataUsingDataContract xmlns="http://tempuri.org/">
      <composite xmlns:a="http://schemas.datacontract.org/2004/07/WcfService2" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
        <a:BoolValue>false</a:BoolValue>
        <a:Name>
          <a:FirstName>BOB</a:FirstName>
        </a:Name>
        <a:StringValue i:nil="true" />
      </composite>
    </GetDataUsingDataContract>
  </s:Body>
</s:Envelope>

UPDATE:

lazyberezovsky helped immensely showing me how Descendents is supposed to work. Be careful of namespaces in XML. Lesson learned. Found another . article with similar issues..

Search XDocument using LINQ without knowing the namespace

Resolved using the following snippet…

var xdoc = XDocument.Parse(xml);
var name = (from p in xdoc.Descendants() where p.Name.LocalName == "FirstName" select p.Value).FirstOrDefault();

Answer 1

When you are using Descendants for finding first occurrence of element, you don’t need to know
structure of file. Following code will work for both your cases:

var xdoc = XDocument.Load(path_to_xml);
var name = (string)xdoc.Descendants("FirstName").FirstOrDefault();

Same with XPath

var name = (string)xdoc.XPathSelectElement("//FirstName[1]");