Cannot find a way to get a child node from an XMLNodeList by text

This is killing me, I have an XMLDocument and I need to be able to get the text value of certain nodes out but everything I try fails. Given the below XML document, I need to get things like the ID of the patient, Last Name, etc.

<Message xmlns="http://" version="010" release="006">
<Header>
    <To Qualifier="C">1306841101</To>
    <From Qualifier="P">8899922</From>
</Header>
<Body>
    <RxFill>
        <Patient>
            <Identification>
      <ID>193306093523</ID>
      <ID3>111223333</ID3>
            </Identification>
            <Name>
                <LastName>Smith</LastName>
                <FirstName>Jane</FirstName>
            </Name>
        </Patient>
    </RxFill>
</Body>

I can get the actual NodeList of 'Patient' like so:

XmlNode root = oDoc.DocumentElement; 
oDoc.GetElementsByTagName("Patient")

but then I am stuck, if I then try to get a child node, the xpath never finds them.

for example:

oDoc.GetElementsByTagName("Patient")[0].SelectSingleNode("Identification")

comes up null even though I can see in the debugger that "Identification" is the FirstChild. I have added slash(es) as well: "//Identification" and no joy.

I can, however, get to it from the document:

oDoc.GetElementsByTagName("Identification")

but that won't work because I may have other tags in the document like that; I only want the Identification tag that belongs to the Patient.

I have tried looping through all the children to find them but that seems very inefficient.

Any ideas?

Solution

You should include the namespace in the XPath. You can do this using an XmlNamespaceManager:

XmlNode root = oDoc.DocumentElement;
XmlNode patient = oDoc.GetElementsByTagName("Patient")[0];

XmlNamespaceManager nsm = new XmlNamespaceManager(new NameTable());
nsm.AddNamespace("ns", "http://");

XmlNode identification = patient.SelectSingleNode("ns:Identification", nsm);
string id = identification.SelectSingleNode("ns:ID", nsm).InnerText;