query deep into xElement using linq-xml

Question

I have XML

<Envelopes>
  <Envelope   xmlns:env="http://www.w3.org/2003/05/soap-envelope">
    <Body>
      <UpdateObjectResponse xmlns="http://www.sap.com/SBO/DIS" 
                            CommandID="UpdateObject picklist">
        <RetKey>426358</RetKey>
        <RetType>156</RetType>
      </UpdateObjectResponse>
    </Body>
  </Envelope>                
  <Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope">
    <Body>
      <UpdateObjectResponse xmlns="http://www.sap.com/SBO/DIS" 
                            CommandID="UpdateObject picklist">
        <RetKey>426358</RetKey>
        <RetType>156</RetType>
      </UpdateObjectResponse>
    </Body>
  </Envelope>
</Envelopes>

and I am trying to get value of RetKey element like so

var query = from t in xdoc.Descendants("Envelope") select t;

foreach (XElement item in query)
{
    var k = item.Element("Body").Element("UpdateObjectResponse").Element("RetKey").Value;
}

var query and item are getting set properly, but I am getting this error within the foreach loop

"Object reference not set to an instance of an object."

i am not sure what i am doing wrongly, but i have tried to solve this for todays now, this is the best way i can put the question on SO — Edwin O., Sep 17 '15 at 13:09

score 1 · Answer 1 · edited May 23 '17 at 10:28

I cannot see anything obvious that's wrong with your code.

I'll assume you're using VS? Try running the following code with a break point in each line of the foreach and chech the locals at each step, to see which of the .Element(..) queries might be the problem. Check each of the variables in in the locals view at each step, to see if something unexpected appears in one of the XElements.

var query = from t in xdoc.Descendants("Envelope") select t;
foreach (XElement item in query)
{
    var j = item;
    var k = item.Element("Body");
    var l = k.Element("UpdateObjectResponse");
    var m = l.Element("RetKey");
    var n = m.Value;
}

Either you will see which of the variables jklmn is different than expected, or the code will break with a more informative exception.

Note: at least in VS2015, there's a little magnifying glass in the locals view, which lets you nicely view XMLs (in case you didn't know).

Edit: I was not aware of the differences between XElement.Descendants and XElement.Elements and I am still unclear on how to do this properly with the cascaded namespaces. See Without or only root namespace. See Strip namespaces from Elements in case the namespace isn't fixed.

I think that this might be the solution, though. If I get it correctly, you can just write

XNamespace ns = "http://www.sap.com/SBO/DIS";
var klist = from t in xdoc.Descendants(ns + "RetKey") select t.Value;

to get a list of the RetKey values in that xml. Maybe also try xdoc.Root.Descendants to avoid the first namespace.

J and K are getting set properly, but l is not , could it be because of the namespace attribute in the updateObjectResponse tag ? — Edwin O., Sep 17 '15 at 14:19
Have you tried what is done [here](http://stackoverflow.com/questions/11229679/how-to-query-xelement-with-two-namespaces)? You probably need to use .Descendants again. — GPMueller, Sep 17 '15 at 14:38
i took off the namesapce in updateObjectResponse element, and it worked, thanks @gMueller — Edwin O., Sep 17 '15 at 21:19

query deep into xElement using linq-xml

1 Answers1