Develop Reference

Access Child nodes with namespace using xpath

How can I read the content of the childnotes using Xpath?
I have already tried this:
var xml = new XmlDocument();
xml.Load("server-status.xml");
var ns = new XmlNamespaceManager(xml.NameTable);
ns.AddNamespace("ns", "namespace");
var node = xml.SelectSingleNode("descendant::ns:server[ns:ip-address]", ns)
Console.WriteLine(node.InnerXml)
But I only get a string like this:
<ip-address>127.0.0.50</ip-address><name>Server 1</name><group>DATA</group>
How can I get the values individually?
Xml file:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<server-status xmlns="namespace">
<server>
<ip-address>127.0.0.50</ip-address>
<name>Server 1</name>
<group>DATA</group>
</server>
</server-status>

You're using XML namespaces in XPath correctly.
However, your original XPath,
descendant::ns:server[ns:ip-address]
says to select all ns:server elements with ns:ip-address children.
If you wish to select the ns:ip-address children themselves, instead use
descendant::ns:server/ns:ip-address
Similarly, you could select ns:name or ns:group elements.

How to Get XML Element by It's 'Value' using XML C# SDK

I have this snippt of XML
<unit class="xxx.xxx.xxx" id="382">
<customId>000</customId>
<description>kg</description>
<key>22452</key>
<Description>Kilogramm</Description>
</unit>
how to get the node 'unit' or parnet of the key element using the value of an element. For instance
i have the value of key element above [22452] and it's Uniqe inside the xml-File.
what i am trying to do getting value of customid [000] of that specific tag.
what i did:
var doc = new XmlDocument();
doc.Load(stream); // stream from xml-file
var key = doc.SelectSingleNode(//key/[text()='" + 22452+ "']"); // that i am not sure about it.
var customId = key.InnerText("customId");

For this kind of query you could either find the node and than navigate to the parent.
Or use XPath:
var unitElemnt = doc.SelectSingleNode("//unit[key = '22452']");
(Assuming I've remembered the XPath to match an element's text content correctly.)
This gets a reference to the <unit> element, by using a relative path to the <key> element in the predicate of the XPath expression.
Generally better to avoid // in XPath for performance, but would need full document structure to do that.

For this you can use Linq to Xml queries.
XElement units = XElement.Load("./Test.xml");
XElement unit = (from item in units.Descendants("unit")
where item.Element("key").Value == "22455"
select item).FirstOrDefault();
string customId = unit.Element("customId").Value;
supposing your xml file look like :
<?xml version="1.0" encoding="utf-8"?>
<units>
<unit class="xxx.xxx.xxx" id="385">
<customId>003</customId>
<description>kg</description>
<key>22455</key>
<Description>Kilogramm</Description>
</unit>
<unit class="xxx.xxx.xxx" id="386">
<customId>004</customId>
<description>kg</description>
<key>22456</key>
<Description>Kilogramm</Description>
</unit>
</units>
for more reading check Microsoft Linq to Xml Docs

C# Find Attribute in XML with another Attribute with Descendants

First I want to find and select the PID"5678" from the <Tool>. With help of this PID, i want to find and select the ID"5678" from the <Parent>. The PID and the ID are the same value, but I have to find it from the <Tool> first.
At the moment I have following Code, to select the first PID. How can I "copy" this value and search with them the Attribute "ID"?
List<string> urls = xmldoc2.Descendants("PID").Select(x => x.Attribute("5678").Value).ToList();
<Tools>
<Tools>
<Tool>
<ID>1234</ID>
<PID>5678</PID>
<Name>Test</Name>
</Tool>
</Tools>
<Type>
<Parent>
<ID>5678</ID>
<PID>9999</PID>
<Name>Test2</Name>
</Parent>
</Type>
</Tools>

Notice that your Xml has multiple Root nodes - which does not work well.
So wrap it into single parent node (i.e. "Root" in below example)
Something of this sort should help you.
string xmlData = #"... Your Xml here....";
var xmlDoc = new XmlDocument();
xmlDoc.LoadXml(xmlData);
var pidNodes = xmlDoc.SelectNodes("//Root/Tools/Tools/Tool/PID");
foreach(XmlNode node in pidNodes)
{
var typeNodeForPid = xmlDoc.SelectSingleNode(string.Format("//Root/Type/Parent[ID = '{0}']", node.InnerText));
}

Replacing an xml element value in c#

Here is my xml file data
<Persons>
<Person>
<Name>john</Name>
</Person>
<Employee>
<Detail>
<Firstname>john</FirstName>
</Detail>
</Employee>
<Student>
<FullName>john</FullName>
</Student>
</Persons>
I want to replace "john" to "danny" in all places.
How can I do this in c# ?

One possible way using XDocument :
var doc = XDocument.Load("path_to_xml_file.xml");
//select all leaf elements having value equals "john"
var elementsToUpdate = doc.Descendants()
.Where(o => o.Value == "john" && !o.HasElements);
//update elements value
foreach(XElement element in elementsToUpdate)
{
element.Value = "danny";
}
//save the XML back as file
doc.Save("path_to_xml_file.xml");
Notice that XElement.Value contains all text nodes within the element, concatenated.
The significance of this is, for example, considering your XML as input, not only <Name> has value of "john" but also <Person>. But we only want to update the leaf elements not the ancestors.
*) I assumed you didn't really meant to tag the question by xmldocument so this answer using the newer XML API XDocument, though using XmlDocument is also possible.

XDocument.XPathSelectElements : I can't seem get the xpath syntax right

I'm trying to work out why my xpath won't select the nodes I specificy
My xpath expression is //DefaultValue, so I expect all elements of name DefaultValue to be selected
My test file (cut down) is :
<?xml version="1.0" encoding="utf-8"?>
<SharedDataSet xmlns:rd="http://schemas.microsoft.com/SQLServer/reporting/reportdesigner" xmlns="http://schemas.microsoft.com/sqlserver/reporting/2010/01/shareddatasetdefinition">
<Description />
<DataSet Name="ddd">
<Query>
<DataSourceReference>xxx</DataSourceReference>
<DataSetParameters>
<DataSetParameter Name="p1">
<DefaultValue>baaaah</DefaultValue> <!-- this node should be selected eh? -->
</DataSetParameter>
<DataSetParameter Name="p2">
<DefaultValue>fooo</DefaultValue> <!-- this node should be selected too eh? -->
</DataSetParameter>
</DataSetParameters>
</Query>
</SharedDataSet>
Code is :
XmlNamespaceManager xn = new XmlNamespaceManager(new NameTable());
xn.AddNamespace("ns", "http://schemas.microsoft.com/sqlserver/reporting/2010/01/shareddatasetdefinition");
xn.AddNamespace("rd", "http://schemas.microsoft.com/SQLServer/reporting/reportdesigner");
xn.AddNamespace("cl", "http://schemas.microsoft.com/sqlserver/reporting/2010/01/componentdefinition");
XDocument document = XDocument.Parse(reportBuffer, LoadOptions.PreserveWhitespace);
IEnumerable<XElement> elements = document.XPathSelectElements(xpath, xn);
at this point elements.Count() equals 0
Can anyone see what foolishness I present?
I can't seem to make the xml demons happy... :-(

The <DefaultValue> element is actually bound to the namespace http://schemas.microsoft.com/sqlserver/reporting/2010/01/shareddatasetdefinition.
The <SharedDataSet> document element has it declared without a prefix, so it is easy to miss. Since <DefaultValue> is a descendant, it inherits the namespace.
If you want to select the <DefaultValue> element you need to adjust your XPath:
//ns:DefaultValue