Question

I’m loading an XML file, getting the values of some nodes and then setting those values into an object.

The problem is that although I can get into the each node, I can’t get its value: it just returns null. Searching in Google and SO I found several threads saying that usually it is a problem of namespaces. So I set up a namespace on the XML file and in my code to work with it. This is now when things get funny:

• If all the nodes but the last one are prefixed (in my code) with the namespace, all of them gets set except that particular one which gives an ArgumentNullException (tabla does not accept nulls on some properties). This seems to be expected behavior.
• if I correct that last line and set up the namespace (as it should be), then the exception gets raised at the FIRST node.

This is the XML:

<?xml version="1.0" encoding="utf-8"?>
<root xmlns="http://daniel.ponticelli.com/ns/dataExport">
  <PollInstance>
    <Poll_Instance_id>1</Poll_Instance_id>
    <POLL_description>Mes 1</POLL_description>
    <dt_start>01/09/2012 12:00:00 a.m.</dt_start>
    <dt_end>30/09/2012 12:00:00 a.m.</dt_end>
    <POLL_status>0</POLL_status>
    <dt_created>03/09/2012 09:50:36 a.m.</dt_created>
    <dt_updated>03/09/2012 09:50:36 a.m.</dt_updated>
    <id_original_clone>0</id_original_clone>
    <target_locs>0</target_locs>
    <id_poll>1</id_poll>
  </PollInstance>
</root>

This is the “wrong” code that has the last element without namespace:

XElement instancia = xml.Descendants().First();
XNamespace ra = "http://daniel.ponticelli.com/ns/dataExport";

tabla.Poll_Instance_id = (int)instancia.Element(ra + "Poll_Instance_id");
tabla.POLL_description = (string)instancia.Element(ra + "POLL_description");
tabla.dt_start = DateTime.Parse((string)instancia.Element(ra + "dt_start"));
tabla.dt_end = DateTime.Parse((string)instancia.Element(ra + "dt_end"));
tabla.POLL_status = (int)instancia.Element(ra + "POLL_status");
tabla.dt_created = DateTime.Parse((string)instancia.Element(ra + "dt_created"));
tabla.dt_updated = DateTime.Parse((string)instancia.Element(ra + "dt_updated"));
tabla.id_original_clone = (int)instancia.Element(ra + "id_original_clone");
tabla.target_locs = (int)instancia.Element(ra + "target_locs");
tabla.id_poll = (int)instancia.Element("id_poll");

The previous code gives the exception on the last line.

Now this is the “correct” code that has all the elements prefixed with the namespace:

XElement instancia = xml.Descendants().First();
XNamespace ra = "http://daniel.ponticelli.com/ns/dataExport";

tabla.Poll_Instance_id = (int)instancia.Element(ra + "Poll_Instance_id");
tabla.POLL_description = (string)instancia.Element(ra + "POLL_description");
tabla.dt_start = DateTime.Parse((string)instancia.Element(ra + "dt_start"));
tabla.dt_end = DateTime.Parse((string)instancia.Element(ra + "dt_end"));
tabla.POLL_status = (int)instancia.Element(ra + "POLL_status");
tabla.dt_created = DateTime.Parse((string)instancia.Element(ra + "dt_created"));
tabla.dt_updated = DateTime.Parse((string)instancia.Element(ra + "dt_updated"));
tabla.id_original_clone = (int)instancia.Element(ra + "id_original_clone");
tabla.target_locs = (int)instancia.Element(ra + "target_locs");
tabla.id_poll = (int)instancia.Element(ra + "id_poll");

This code now gives the exception on the third line! (the one that begins with tabla.Poll_Instance_id). If I set a breakpoint on the “wrong” code just before the last line, I can check in VS that indeed the values are being retrieved from the XML and set on the object tabla as expected; so I don’t know what’s going on.

Answer 1

I have found the solution, thanks to @lazyberezovsky for pointing me to the right direction with the root() thing.

The problem was on the Descendants() method, which gives me all the descendant nodes; so I was getting the PollInstance node and also the Poll_instance_id and the others. That’s why it breaks on the first line in the “right” code: after processing the first node, it choked on the others.

Instead I have to use the Elements() method which returns only the direct childs; in my case, only the PollInstance.