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Linq to XML with Namespace Prefix Not Working

I have been working from Scott Allen's Puralsight course on Linq Fundamentals and this linked section describes reading xml with Namespace prefixes, yet I'm not able to make this work.
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<OutboundEvent
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:abb.com:assetsuite:IF:Event http://apifw/devifa/xml/GeneralLedger/GeneralLedger.Publish.Event.V940.xsd"
xmlns="urn:abb.com:assetsuite:IF:Event"
xmlns:hdr="urn:abb.com:assetsuite:IF:Header"
xmlns:bo="urn:abb.com:assetsuite:IF:BO"
xmlns:boe="urn:abb.com:assetsuite:IF:IFExtension"
>
...
<bo:BusinessObject>
...
</bo:BusinessObject>
</OutboundEvent>
I should be getting a single XElement returned from the following code, yet I am not:
var document = XDocument.Load(path);
var bo = (XNamespace)"urn:abb.com:assetsuite:IF:BO";
var businessobjects =
from elements in document.Element("OutboundEvent")?.Elements(bo + "BusinessObject")
?? Enumerable.Empty<XElement>()
select elements;

The OutboundEvent node is in a namespace but your code references it as if it wasn't. It is in the urn:abb.com:assetsuite:IF:Event namespace.
XNamespace ns = "urn:abb.com:assetsuite:IF:Event";
XNamespace bo = "urn:abb.com:assetsuite:IF:BO";
var businessObjects =
document.Elements(ns + "OutboundEvent").Elements(bo + "BusinessObject");

Shouldn't you define and use the default namespace for OutboundEvent element?
var document = XDocument.Load(path);
var ns = (XNamespace)"urn:abb.com:assetsuite:IF:Event";
var bo = (XNamespace)"urn:abb.com:assetsuite:IF:BO";
var businessobjects =
from elements in document.Element(ns + "OutboundEvent")?.Elements(bo + "BusinessObject")
?? Enumerable.Empty<XElement>()
select elements;

Finding a set of nodes in an XML [duplicate]

Can't get any result in feeds.
feedXML has the correct data.
XDocument feedXML = XDocument.Load(#"http://search.twitter.com/search.atom?q=twitter");
var feeds = from entry in feedXML.Descendants("entry")
select new
{
PublicationDate = entry.Element("published").Value,
Title = entry.Element("title").Value
};
What am I missing?

You need to specify the namespace:
// This is the default namespace within the feed, as specified
// xmlns="..."
XNamespace ns = "http://www.w3.org/2005/Atom";
var feeds = from entry in feedXML.Descendants(ns + "entry")
...
Namespace handling is beautifully easy in LINQ to XML compared with everything other XML API I've ever used :)

You need to specify a namespace on both the Descendents and Element methods.
XDocument feedXML = XDocument.Load(#"http://search.twitter.com/search.atom?q=twitter");
XNamespace ns = "http://www.w3.org/2005/Atom";
var feeds = from entry in feedXML.Descendants(ns + "entry")
select new
{
PublicationDate = entry.Element(ns + "published").Value,
Title = entry.Element(ns + "title").Value
};

If you look at the XML returned by the HTTP request, you will see that it has an XML namespace defined:
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" ...>
<id>tag:search.twitter.com,2005:search/twitter</id>
...
</feed>
XML is just like C#, if you use an element name with the wrong namespace, it is not considered to be the same element! You need to add the required namepsace to your query:
private static string AtomNamespace = "http://www.w3.org/2005/Atom";
public static XName Entry = XName.Get("entry", AtomNamespace);
public static XName Published = XName.Get("published", AtomNamespace);
public static XName Title = XName.Get("title", AtomNamespace);
var items = doc.Descendants(AtomConst.Entry)
.Select(entryElement => new FeedItemViewModel()
new {
Title = entryElement.Descendants(AtomConst.Title).Single().Value,
...
});

The issue is in feedXML.Descendants("entry"). This is returning 0 results
According to the documentation you need to put in a fully qualified XName

Deleting node from string with xml structure

I have an string parameter with xml content in it. Basically the string have an XML inside.
string S = funcThatReturnsXML (parameters);
S have the next text:
<?xml version="1.0" encoding="utf-8" ?>
<tagA>
<tagB>
<tagBB>
..
.
.
</tagBB>
.
.
</tagB>
<tagC>
..
..
.
</tagC>
</tagA>
The funcThatReturnsXML (parameters) creates an XmlDocument object but the return it as a string, I cant change this function, to much stuff works with it.
Tried to create XmlDocument objetc but the SelectSingleNode return null.
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.LoadXml(S);
XmlNode root = xmlDoc.SelectSingleNode("tagB");
How can I delete from string S (not XML Object) specific node, for example <tagB>
EDIT: this is the XML I tested with:
<?xml version="1.0" ?>
- <Request xmlns:xsi="http://www.mysite.com" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
- <info xmlns="http://www.mysite.com">
<RequestTR>54</RequestTR>
<time>2013-12-22</time>
</info>
- <Parameters xmlns="http://www.mysite.com">
<id>3</id>
<name>2</name>
</Parameters>
<title>Request</title>
</Request>

Try this:
string S = funcThatReturnsXML(parameters);
var doc = XDocument.Parse(S);
var nodeToRemove = doc.Descendants("tagB");
nodeToRemove.Remove();
That will remove all nodes named "tagB" from string S which contains xml.
UPDATE 1:
Sorry, i missed to include one more line:
S = doc.ToString();
My first code above removed "tagB" from doc but didnt save it back to S variable.
UPDATE 2:
I tested with following xml which contain attribute:
<tagA attribute="value">
<tagB>
<tagBB>
</tagBB>
</tagB>
<tagC></tagC>
</tagA>
and the output of Console.WriteLine(S):
<tagA attribute="value">
<tagC></tagC>
</tagA>
UPDATE 3:
Given your updated xml format, I know why my previous code didn't work for you. That was because your xml have namespace (xmlns) declared. The solution is to use LocalName when searching for the node to be removed, that will search for node name while ignoring its namespace. The follwoing example shows how to remove all "info" node:
var doc = XDocument.Parse(S);
var nodeToRemove = doc.Descendants().Where(o => o.Name.LocalName == "info");
nodeToRemove.Remove();
S = doc.ToString();

If you can determine the particular outer element to remove from the returned XML, you could use LINQ to XML:
var returnedXml = funcThatReturnsXML(parameters);
var xmlElementToRemove = funcThatReturnsOuterElement(returnedXml);
var xelement = XElement.Load("XmlDoc.txt");
xelement.Elements().Where(e => e.Name == xmlElementToRemove).Remove();
For example:
using System.Linq;
using System.Xml.Linq;
class Program
{
static void Main(string[] args)
{
// pretend this is the funThatReturnsXML return value
var returnedXml = "<tagB><tagBB></tagBB></tagB>";
// get the outer XML element name
var xmlElementToRemove = GetOuterXmlElement(returnedXml);
// load XML from where ever
var xelement = XElement.Load("XmlDoc.txt");
// remove the outer element and all subsequent elements
xelement.Elements().Where(e => e.Name == xmlElementToRemove).Remove();
}
static string GetOuterXmlElement(string xml)
{
var index = xml.IndexOf('>');
return xml.Substring(1, index - 1);
}
}
Note that the above is a "greedy" removal method, if there is more than once element with the name returned via the GetOuterXmlElemet method they will all be removed. If you want a specific instance to be removed then you will require something more sophisticated.

Building on your edit:
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.LoadXml(S);
var nodeA = xmlDoc.SelectSingleNode("/tagA");
var nodeB = nodeA.SelectSingleNode("tagB");
nodeA.RemoveChild(nodeB);
To remove (possibly) multiple tagB nodes in unknown positions, you may try:
var bees = xmlDoc.SelectNodes("//tagB");
foreach (XmlNode bee in bees) {
var parent = bee.ParentNode;
parent.RemoveChild(bee);
}

Parsing specific part of XML file

I have a .gpx XML file with the following sample:
<trk>
<name>Test</name>
<trkseg>
<trkpt lon="-84.89032996818423" lat="32.75810896418989">
<ele>225.0</ele>
<time>2011-04-02T11:57:48.000Z</time>
<extensions>
<gpxtpx:TrackPointExtension>
<gpxtpx:cad>0</gpxtpx:cad>
</gpxtpx:TrackPointExtension>
</extensions>
</trkpt>
</trkseg>
</trk>
I'm using Linq to XML to parse this but I'm having a difficult time parsing the extensions section. Here's the code I'm using:
var gpxDoc = LoadFromStream(document);
var gpx = GetGpxNameSpace();
var gpxtpx = XNamespace.Get("gpxtpx");
var tracks = from track in gpxDoc.Descendants(gpx + "trk")
select new
{
Name = DefaultStringValue(track, gpx, "name"),
Description = DefaultStringValue(track, gpx, "desc"),
Segments = (from trkSegment in track.Descendants(gpx + "trkseg")
select new
{
TrackSegment = trkSegment,
Points = (from trackpoint in trkSegment.Descendants(gpx + "trkpt")
select new
{
Lat = Double(trackpoint.Attribute("lat").Value),
Lng = Double(trackpoint.Attribute("lon").Value),
Ele = DefaultDoubleValue(trackpoint, gpx, "ele"),
Time = DefaultDateTimeValue(trackpoint, gpx, "time"),
Extensions = (
from ext in trackpoint.Descendants(gpx + "extensions").Descendants(gpxtpx + "TrackPointExtension")
select new
{
Cad = DefaultIntValue(ext, gpxtpx, "cad")
}).SingleOrDefault()
})
})
};
Here's the relevant helper code:
private static double? DefaultIntValue(XContainer element, XNamespace ns, string elementName)
{
var xElement = element.Element(ns + elementName);
return xElement != null ? Convert.ToInt32(xElement.Value) : (int?)null;
}
private XNamespace GetGpxNameSpace()
{
var gpx = XNamespace.Get("http://www.topografix.com/GPX/1/1");
return gpx;
}
The actual error I'm getting is
The following error occurred: Object reference not set to an instance of an object.
and it bombs on this code:
Extensions = (from ext in trackpoint.Descendants(gpx + "extensions").Descendants(gpxtpx + "TrackPointExtension")
select new
{
Cad = DefaultIntValue(ext, gpxtpx, "cad")
}).SingleOrDefault();
I just don't know how to fix it.

Since you never declare the namespace (xmlns:gpxtpx="http://www.topografix.com/GPX/1/1") it is never going to match. The xml fragment you provided is not well formed due to the lack of the namespace.
If the fragment posted is snipped from a larger document, consider switching to XML API's rather than string manipulation. If that is the entirety of the XML you receive from an outside system, add it to a root node which you can declare the schema in:
<root xmlns:gpxtpx="http://www.topografix.com/GPX/1/1">
<!-- put your xml fragment here -->
</root>

I am trying to read directory from xml file in c# and have problem

<?xml version="1.0" encoding="UTF-8"?>
<form:Documents xmlns:form="http://www.abbyy.com/FlexiCapture/Schemas/Export/FormData.xsd" xmlns:addData="http://www.abbyy.com/FlexiCapture/Schemas/Export/AdditionalFormData.xsd">
<_Document_Definition_1:_Document_Definition_1 addData:ImagePath="C:\POC\Export\Test.pdf" xmlns:_Document_Definition_1="http://www.abbyy.com/FlexiCapture/Schemas/Export/Document_Definition_1.xsd">
<_Page_1>
<_First_Name>John</_First_Name>
<_Last_Name>Doe</_Last_Name>
</_Page_1>
</_Document_Definition_1:_Document_Definition_1>
</form:Documents>
I have xml containing directory of pdf file which I would need to read.
I can read first name and last name from _Page_1 node but do not know how to read ImagePath.
Here is my code to read from _Page_1
XDocument xDoc = XDocument.Load("Test.xml");
var poc = from p in xDoc.Descendants("_Page_1")
select new
{
FirstName = p.Element("_First_Name").Value,
LastNumber = p.Element("_Last_Name").Value
};
// Execute the query
foreach (var customer in poc)
{
Console.WriteLine(customer.FirstName);
Console.WriteLine(customer.LastName);
}
//Pause the application
Console.ReadLine();
Thank you BrokenGlass, it's working.
I have one more question.
What if I have several iteration of _Document_Definition node, how do I read each iteration.
<?xml version="1.0" encoding="UTF-8"?>
<form:Documents xmlns:form="http://www.abbyy.com/FlexiCapture/Schemas/Export/FormData.xsd" xmlns:addData="http://www.abbyy.com/FlexiCapture/Schemas/Export/AdditionalFormData.xsd">
<_Document_Definition_1:_Document_Definition_1 addData:ImagePath="C:\POC\Export\Test.pdf" xmlns:_Document_Definition_1="http://www.abbyy.com/FlexiCapture/Schemas/Export/Document_Definition_1.xsd">
<_Page_1>
<_First_Name>John</_First_Name>
<_Last_Name>Doe</_Last_Name>
</_Page_1>
</_Document_Definition_1:_Document_Definition_1>
<_Document_Definition_1:_Document_Definition_1 addData:ImagePath="C:\POC\Export\Test2.pdf" xmlns:_Document_Definition_1="http://www.abbyy.com/FlexiCapture/Schemas/Export/Document_Definition_1.xsd">
<_Page_1>
<_First_Name>Jane</_First_Name>
<_Last_Name>Doe</_Last_Name>
</_Page_1>
</_Document_Definition_1:_Document_Definition_1>
</form:Documents>

You are missing the XML namespace references to access those attributes, this works:
XDocument doc = XDocument.Load(#"test.xml");
XNamespace _Document_Definition_1 = "http://www.abbyy.com/FlexiCapture/Schemas/Export/Document_Definition_1.xsd";
XNamespace addData = "http://www.abbyy.com/FlexiCapture/Schemas/Export/AdditionalFormData.xsd";
string impagePath = doc.Descendants(_Document_Definition_1 + "_Document_Definition_1")
.First()
.Attribute(addData + "ImagePath")
.Value;

It looks like Imagepath is an attribute not an element. Hence you are not able to read it. Check for the attributes in the xml file.