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I'm unable to extract the Data from this XML

I'm currently working on a small weather application in C#. To do this, I need to extract data from this xml file: http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22london%22&format=xml
In this specific case I need the value of the first /query/results/place/woeid node. I've been looking around and tried many different methods, but didn't manage to get any values with any of those. My current code looks like this:
string query = String.Format("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22london%22&format=xml");
XmlDocument xml = new XmlDocument();
xml.Load(query);
XmlNodeList nodeList = wData.DocumentElement.SelectNodes("/query/results/place");
foreach (XmlNode node in nodeList)
{
return node.SelectSingleNode("woeid").InnerText;
}
return "NO WOEID FOUND!";
I'm just starting to learn C# so I might do some stupid mistakes. Still, I would really appreciate any kind of help.

You can use XDocument
string query = String.Format("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22london%22&format=xml");
XDocument xml = XDocument.Load(query);
XNamespace ns = "http://where.yahooapis.com/v1/schema.rng";
var woeid = xml.Element("query").Element("results").Elements(ns + "place").FirstOrDefault().Element(ns +"woeid").Value;
Make sure you check if there are any elements in the XDocuments

NodeList.SelectSingleNode() syntax

Having problems getting NodeList.SelectSingleNode() to work properly.
My XML looks like this:
<?xml version="1.0" encoding="ISO-8859-1" standalone="yes"?>
<inm:Results xmlns:inm="http://www.namespace.com/1.0">
<inm:Recordset setCount="18254">
<inm:Record setEntry="0">
<!-- snip -->
<inm:Image>fileName.jpg</inm:Image>
</inm:Record>
</inm:Recordset>
</inm:Results>
The data is a long series of <inm:Record> entries.
I open the doc and get create a NodeList object based on "inm:Record". This works great.
XmlDocument xdoc = new XmlDocument();
xdoc.Load(openFileDialog1.FileName);
XmlNodeList xRecord = xdoc.GetElementsByTagName("inm:Record");
I start looping through the NodeList using a for loop. Before I process a given entry, I want to check and see if the <inm:Image> is set. I thought it would be super easy just to do
string strImage = xRecord[i].SelectSingleNode("inm:Image").InnerText;
My thinking being, "For the XRecord that I'm on, go find the <inm:Image> value ...But this doesn't work as I get the exception saying that I need a XmlNameSpaceManager. So, I tried to set that up but could never get the syntax right.
Can someone show me how to use the correct XmlNameSpaceManager syntax in this case.
I've worked around the issue for now by looping through all of the childNodes for a given xRecord, and checking the tag once I loop around to it. I would like to check that value first to see if I need to loop over that <inm:Record> entry at all.

No need to loop through all the Record elements, just use XPath to specify the subset that you want:
XmlDocument xdoc = new XmlDocument();
xdoc.Load(openFileDialog1.FileName);
XmlNamespaceManager manager = new XmlNamespaceManager(xdoc.NameTable);
manager.AddNamespace("inm", "http://www.inmagic.com/webpublisher/query");
XmlNodeList nodes = xdoc.SelectNodes("/inm:Results/inm:Recordset/inm:Record[inm:Image != '']", manager);

Using the LINQ to XML libraries, here's an example for retrieving that said node's value:
XDocument doc = XDocument.Load(openFileDialog1.FileName);
List<XElement> docElements = doc.Elements().ToList();
XElement results = docElements.Elements().Where(
ele => ele.Name.LocalName == "Results").First();
XElement firstRecord = results.Elements().Where(
ele => ele.Name.LocalName == "Record").First();
XElement recordImage = firstRecord .Elements().Where(
ele => ele.Name.LocalName == "Image").First();
string imageName = recordImage.Value;
Also, by the way, using Hungarian notation for a type-checked language is overkill. You don't need to prepend string variables with str when it will always be a string.

XmlNamespaceManager nsMgr = new XmlNamespaceManager(xdoc.NameTable);
string strImage = xRecord[i].SelectSingleNode("inm:Image",nsMgr).InnerText;
Should do it.

Using this Xml library, you can get all the records that have an Image child element with this:
XElement root = XElement.Load(openFileDialog1.FileName);
XElement[] records = root.XPath("//Record[Image]").ToArray();
If you want to be sure that the Image child contains a value, it can be expressed like this:
XElement[] records = root.XPath("//Record[Image != '']").ToArray();

C# Xml Value always getting null

I have the following Xml in my Resources.xmltest:
<?xml version="1.0" encoding="utf-8" ?>
<Response xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://DFISofft.com/SmartPayments/">
<Result>0</Result>
<Message>Pending</Message>
<PNRef>222131</PNRef>
<ExtData>InvNum=123</ExtData>
</Response>
I've tried several ways to get the values, Result,Message,PNRef,ExtData, out of it and I've had no luck. I always get a null value for the NodePath so it never goes into the loop:
var XmlDoc = new XmlDocument();
XmlDoc.LoadXml(Resources.xmltest);
XmlElement NodePath = (XmlElement) XmlDoc.SelectSingleNode("/Response");
while (NodePath != null)
{
foreach (XmlNode Xml_Node in NodePath)
{
Console.WriteLine(Xml_Node.Name + " " + Xml_Node.InnerText);
}
}
I've tried this:
XmlNode node3 = XmlDoc.SelectSingleNode("PNRef");
Console.WriteLine(node3.Value);
Console.WriteLine(XmlDoc.InnerXml);
var tst = XmlDoc.GetElementsByTagName("PNRef");
Console.WriteLine(tst);
And this:
NodePath = (XmlElement) XmlDoc.SelectSingleNode("/Response");
if (NodePath != null)
{
foreach (XmlNode node in NodePath)
{
Console.WriteLine("NodeName: " + Xml_NodeX.Name);
Console.WriteLine("NodeValue: " + node.InnerText);
}
}
Apparently, I'm not getting the xml read/write. I've done it with DataSets but they do all the work for you.
Can someone point me in the right direction? I've been at this for longer than I should have been already.
Thank you!

Your XML has a XML namespace and you're not paying any attention to it:
<Response xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://DFISofft.com/SmartPayments/">
******************************************
When selecting from this XML, you need to use that XML namespace!
You're not taking into account the XML namespace (xmlns="http://nts-de-osm1-pxc/webservices/") on the document!
Try this:
var XmlDoc = new XmlDocument();
// setup the XML namespace manager
XmlNamespaceManager mgr = new XmlNamespaceManager(XmlDoc.NameTable);
// add the relevant namespaces to the XML namespace manager
mgr.AddNamespace("ns", "http://DFISofft.com/SmartPayments/");
XmlDoc.LoadXml(Resources.xmltest);
// **USE** the XML anemspace in your XPath !!
XmlElement NodePath = (XmlElement) XmlDoc.SelectSingleNode("/ns:Response");
while (NodePath != null)
{
foreach (XmlNode Xml_Node in NodePath)
{
Console.WriteLine(Xml_Node.Name + " " + Xml_Node.InnerText);
}
}

The problem is your XPath query, which doesn't specify a namespace - despite the fact that your document only has a Response element in the "http://DFISofft.com/SmartPayments/" namespace. Ditto the PNRef elements.
Personally I'd use LINQ to XML if I actually wanted to use namespaces if at all possible. For example:
XNamespace ns = "http://DFISofft.com/SmartPayments/";
XDocument doc = XDocument.Load(filename);
foreach (var element in doc.Descendants(ns + "PNRef"))
{
// Use element here
}
As you can see, LINQ to XML makes it really easy to use namespaces - but of course it requires .NET 3.5 or higher. If I had to use .NET 2.0, I'd either use XmlNamespaceManager or iterate manually and check local names instead of using XPath.

That is because the node isn't called response; you need to take the namespace into account:
var XmlDoc = new XmlDocument();
var nsmgr = new XmlNamespaceManager(XmlDoc.NameTable);
nsmgr.AddNamespace("x", "http://DFISofft.com/SmartPayments/");
XmlDoc.LoadXml(yourXml);
XmlElement NodePath = (XmlElement)XmlDoc.SelectSingleNode("/x:Response", nsmgr);

For future reference...
Bubba Soft
This site has a great free tool for building XPath Expressions (XPath Builder).

It's because you are using the overload of SelectSingleNode that assumes an empty namespace. Since you have a default namespace you will need to use the version that takes an XmlNamespaceManager. See this article for more info.
from the docs:
If the XPath expression does not include a prefix, it is assumed that the namespace URI is the empty namespace. If your XML includes a default namespace, you must still add a prefix and namespace URI to the XmlNamespaceManager; otherwise, you will not get a node selected. For more information, see Select Nodes Using XPath Navigation.

SelectSingleNode return null - even with namespace

I know this question has been asked in a similar fashion before, but I can't seem to get this working.
I have some xml:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<Research xmlns="http://www.rixml.org/2005/3/RIXML" xmlns:xalan="http://xml.apache.org/xalan" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" createDateTime="2011-03-29T15:41:48Z" language="eng" researchID="MusiJvs3008">
<Product productID="MusiJvs3008">
<StatusInfo currentStatusIndicator="Yes" statusDateTime="2011-03-29T15:41:48Z" statusType="Published" />
<Source>
<Organization type="SellSideFirm" primaryIndicator="Yes">
<OrganizationID idType="Reuters">9999</OrganizationID>
And I'm trying to read values using xpath:
XPathDocument xmldoc = new XPathDocument(xmlFile);
XPathNavigator nav = xmldoc.CreateNavigator();
XmlNamespaceManager nsMgr = new XmlNamespaceManager(nav.NameTable);
nsMgr.AddNamespace(string.Empty, "http://www.rixml.org/2005/3/RIXML");
XPathNavigator result = nav.SelectSingleNode("/Research", nsMgr); // <-- Returns null!
But even a simple select of the root node returns null! I am sure I have something wrong with my namespace. Can someone please help?
Ideally I want simple lines that will let me select values from the xml file, i.e.
String a = xmlDoc.SelectSingleNode(#"/Research/Product/Content/Title").Value;
BTW, I have no (direct) control over the XML file content.

I don't believe you can use an empty namespace alias and have it used automatically by the XPath expression. As soon as you use an actual alias, it should work though. This test is fine, for example:
using System;
using System.Xml;
using System.Xml.XPath;
class Test
{
static void Main()
{
string xmlFile = "test.xml";
XPathDocument xmldoc = new XPathDocument(xmlFile);
XPathNavigator nav = xmldoc.CreateNavigator();
XmlNamespaceManager nsMgr = new XmlNamespaceManager(nav.NameTable);
nsMgr.AddNamespace("x", "http://www.rixml.org/2005/3/RIXML");
XPathNavigator result = nav.SelectSingleNode("/x:Research", nsMgr);
Console.WriteLine(result);
}
}
Do you have to use XPath and XPathDocument, by the way? I tend to find that LINQ to XML is a much more pleasant API, particularly when it comes to namespaces. If you're using .NET 3.5 and you have no particular requirement to use XPath, I'd suggest you check it out.

Make the following changes
nsMgr.AddNamespace("x", "http://www.rixml.org/2005/3/RIXML");
XPathNavigator result = nav.SelectSingleNode("/x:Research", nsMgr);

i could post, and answer my own question, for the native equivalent of this code. Instead i'll just add it as an answer to the end.
When using the native IXMLDOMDocument (version 6) object:
//Give the default namespace as alias of "x"
document.setProperty("SelectionNamespaces","xmlns:x='http://www.rixml.org/2005/3/RIXML'");
//Query for the nodes we want
document.selectSingleNode("/x:Research");
Bonus Question: Why, oh why, does no Xml Document object model query the default namespace when no namespace is specified... sigh

SelectSingleNode returning null for known good xml node path using XPath

Consider this simple XML document. The serialized XML shown here is the result of an XmlSerializer from a complex POCO object whose schema I have no control over.
<My_RootNode xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="">
<id root="2.16.840.1.113883.3.51.1.1.1" extension="someIdentifier" xmlns="urn:hl7-org:v3" />
<creationTime xsi:nil="true" xmlns="urn:hl7-org:v3" />
</My_RootNode>
The goal is to extract the value of the extension attribute on the id node. In this case, we are using the SelectSingleNode method, and given an XPath expression as such:
XmlNode idNode = myXmlDoc.SelectSingleNode("/My_RootNode/id");
//idNode is evaluated to null at this point in the debugger!
string msgID = idNode.Attributes.GetNamedItem("extension").Value;
The problem is that the SelectSingleNode method returns null for the given XPath expression.
Question: any ideas on this XPath query's correctness, or why this method call + XPath expression would return a null value? Perhaps the namespaces are part of the problem?

I strongly suspect the problem is to do with namespaces. Try getting rid of the namespace and you'll be fine - but obviously that won't help in your real case, where I'd assume the document is fixed.
I can't remember offhand how to specify a namespace in an XPath expression, but I'm sure that's the problem.
EDIT: Okay, I've remembered how to do it now. It's not terribly pleasant though - you need to create an XmlNamespaceManager for it. Here's some sample code that works with your sample document:
using System;
using System.Xml;
public class Test
{
static void Main()
{
XmlDocument doc = new XmlDocument();
XmlNamespaceManager namespaces = new XmlNamespaceManager(doc.NameTable);
namespaces.AddNamespace("ns", "urn:hl7-org:v3");
doc.Load("test.xml");
XmlNode idNode = doc.SelectSingleNode("/My_RootNode/ns:id", namespaces);
string msgID = idNode.Attributes["extension"].Value;
Console.WriteLine(msgID);
}
}

If you want to ignore namespaces completely, you can use this:
static void Main(string[] args)
{
string xml =
"<My_RootNode xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns=\"\">\n" +
" <id root=\"2.16.840.1.113883.3.51.1.1.1\" extension=\"someIdentifier\" xmlns=\"urn:hl7-org:v3\" />\n" +
" <creationTime xsi:nil=\"true\" xmlns=\"urn:hl7-org:v3\" />\n" +
"</My_RootNode>";
XmlDocument doc = new XmlDocument();
doc.LoadXml(xml);
XmlNode idNode = doc.SelectSingleNode("/*[local-name()='My_RootNode']/*[local-name()='id']");
}

This should work in your case without removing namespaces:
XmlNode idNode = myXmlDoc.GetElementsByTagName("id")[0];

Sorry, you forgot the namespace. You need:
XmlNamespaceManager ns = new XmlNamespaceManager(myXmlDoc.NameTable);
ns.AddNamespace("hl7","urn:hl7-org:v3");
XmlNode idNode = myXmlDoc.SelectSingleNode("/My_RootNode/hl7:id", ns);
In fact, whether here or in web services, getting null back from an XPath operation or anything that depends on XPath usually indicates a problem with XML namespaces.

Just to build upon solving the namespace issues, in my case I've been running into documents with multiple namespaces and needed to handle namespaces properly. I wrote the function below to get a namespace manager to deal with any namespace in the document:
private XmlNamespaceManager GetNameSpaceManager(XmlDocument xDoc)
{
XmlNamespaceManager nsm = new XmlNamespaceManager(xDoc.NameTable);
XPathNavigator RootNode = xDoc.CreateNavigator();
RootNode.MoveToFollowing(XPathNodeType.Element);
IDictionary<string, string> NameSpaces = RootNode.GetNamespacesInScope(XmlNamespaceScope.All);
foreach (KeyValuePair<string, string> kvp in NameSpaces)
{
nsm.AddNamespace(kvp.Key, kvp.Value);
}
return nsm;
}

Well... I had the same issue and it was a headache. Since I didn't care much about the namespace or the xml schema, I just deleted this data from my xml and it solved all my issues. May not be the best answer? Probably, but if you don't want to deal with all of this and you ONLY care about the data (and won't be using the xml for some other task) deleting the namespace may solve your problems.
XmlDocument vinDoc = new XmlDocument();
string vinInfo = "your xml string";
vinDoc.LoadXml(vinInfo);
vinDoc.InnerXml = vinDoc.InnerXml.Replace("xmlns=\"http://tempuri.org\/\", "");

The rule to keep in mind is: if your document specifies a namespace, you MUST use an XmlNamespaceManager in your call to SelectNodes() or SelectSingleNode(). That's a good thing.
See the article Advantages of namespaces . Jon Skeet does a great job in his answer showing how to use XmlNamespaceManager. (This answer should really just be a comment on that answer, but I don't quite have enough Rep Points to comment.)

just use //id instead of /id. It works fine in my code

Roisgoen's answer worked for me, but to make it more general, you can use a RegEx:
//Substitute "My_RootNode" for whatever your root node is
string strRegex = #"<My_RootNode(?<xmlns>\s+xmlns([\s]|[^>])*)>";
var myMatch = new Regex(strRegex, RegexOptions.None).Match(myXmlDoc.InnerXml);
if (myMatch.Success)
{
var grp = myMatch.Groups["xmlns"];
if (grp.Success)
{
myXmlDoc.InnerXml = myXmlDoc.InnerXml.Replace(grp.Value, "");
}
}
I fully admit that this is not a best-practice answer, but but it's an easy fix and sometimes that's all we need.