Develop Reference

Customizing an XML element using LINQ To XML

I have the following code:
XNamespace testNM = "urn:lst-emp:emp";
XDocument xDoc;
string path = "project_data.xml";
if (!File.Exists(path))
{
xDoc = new XDocument(
new XDeclaration("1.0", "UTF-16", null),
new XElement(testNM + "Test")
);
}
else
{
xDoc = XDocument.Load(path);
}
var element = new XElement("key",
new XElement("Type", type),
new XElement("Value", value));
xDoc.Element(testNM + "Test").Add(element);
// Save to Disk
xDoc.Save(path);
which produces an output in the XML file like this:
<?xml version="1.0" encoding="utf-16"?>
<Test xmlns="urn:lst-emp:emp">
<key xmlns="">
<Type>String</Type>
<Value>somestring</Value>
</key>
</Test>
How can I get an output like this in the XML file instead?
<?xml version="1.0" encoding="utf-16"?>
<Tests xmlns="urn:lst-emp:emp">
<key name="someString">
<Type>String</Type>
<Value>somestring</Value>
</key >
</Tests>
Note its only the 3rd line that has changed in the XML file.

You can do it this way:
var element = new XElement("key",
new XAttribute("name", "someString"),
new XElement("Type", "type"),
new XElement("Value", "value"));

To provide a complete version of Bilyukov's answer, this should produce the output expected. Obviously substitute the "someString" static string with a variable populated as you wish. Changes include using XName.Get(string, string) to create the appropriate XName objects for the XElement constructors.
XNamespace testNM = "urn:lst-emp:emp";
XDocument xDoc;
string path = "project_data.xml";
if (!File.Exists(path))
{
xDoc = new XDocument(
new XDeclaration("1.0", "UTF-16", null),
new XElement(XName.Get("Tests", testNM.NamespaceName))
);
}
else
{
xDoc = XDocument.Load(path);
}
var element = new XElement(XName.Get("key", testNM.NamespaceName),
new XAttribute("name", "someString"),
new XElement("Type", type),
new XElement("Value", value));
xDoc.Element(XName.Get("Tests", testNM.NamespaceName)).Add(element);
// Save to Disk
xDoc.Save(path);

Your XML has default namespace. Descendants of the element where default namespace declared is considered in the same default namespace, unless it is explicitly declared with different namespace. That's why you need to use the same XNamespace for <key> element. :
var element = new XElement(testNM +"key",
new XAttribute("name", "someString"),
new XElement(testNM +"Type", type),
new XElement(testNM +"Value", value));

How to specify an xmlns for XDocument?

I tried:
textBox1.Text = new XDocument(new XDeclaration("1.0", "UTF-8", "yes"),
new XElement("root1", new XAttribute( "xmlns", #"http://example.com"), new XElement("a", "b"))
).ToString();
But I get:
The prefix '' cannot be redefined from '' to 'http://example.com' within the same start element tag.
I also tried substituting (according to an answer I found) :
XAttribute(XNamespace.Xmlns,...
But got an error as well.
Note: I'm not trying to have more than one xmlns in the document.

The way the XDocument API works with namespace-scoped names is as XName instances. These are fairly easy to work with, as long as you accept that an XML name isn't just a string, but a scoped identifier. Here's how I do it:
var ns = XNamespace.Get("http://example.com");
var doc = new XDocument(new XDeclaration("1.0", "utf-8", null));
var root = new XElement(ns + "root1", new XElement(ns + "a", "b"));
doc.Add(root);
Result:
<root1 xmlns="http://example.com">
<a>b</a>
</root1>
Note the + operator is overloaded to accept an XNamespace and a String to result in and XName instance.

Linq to XML, C#

I have an xml in XDocument object (LINQ to XML). I need to add the namespace to each Xelement/node in the Xdocument.
I dont want to add in the below way. beceause i already have the xml in xdoc.
XDocument xDoc = new XDocument(
new XElement(ns + "root",
new XElement(ns + "person",
new XAttribute("id", 1),
new XElement(ns + "firstname", "jack"),
Below is the format i have
<root>
<person>1</person>
<firstname>jack</firstname>
</root>
I want to convert it to this below format
<emp:root>
<emp:person>1</emp:person>
<emp:firstname>jack</emp:firstname>
</emp:root>

foreach (var node in xDoc.Descendants())
{
node.Name = ns + node.Name.LocalName;
}
That should work:
Side note the namespace will only appear on the root node.

XElement namespaces (How to?)

How to create xml document with node prefix like:
<sphinx:docset>
<sphinx:schema>
<sphinx:field name="subject"/>
<sphinx:field name="content"/>
<sphinx:attr name="published" type="timestamp"/>
</sphinx:schema>
When I try to run something like new XElement("sphinx:docset") i getting exception
Unhandled Exception: System.Xml.XmlException: The ':' character, hexadecimal val
ue 0x3A, cannot be included in a name.
at System.Xml.XmlConvert.VerifyNCName(String name, ExceptionType exceptionTyp
e)
at System.Xml.Linq.XName..ctor(XNamespace ns, String localName)
at System.Xml.Linq.XNamespace.GetName(String localName)
at System.Xml.Linq.XName.Get(String expandedName)

It's really easy in LINQ to XML:
XNamespace ns = "sphinx";
XElement element = new XElement(ns + "docset");
Or to make the "alias" work properly to make it look like your examples, something like this:
XNamespace ns = "http://url/for/sphinx";
XElement element = new XElement("container",
new XAttribute(XNamespace.Xmlns + "sphinx", ns),
new XElement(ns + "docset",
new XElement(ns + "schema"),
new XElement(ns + "field", new XAttribute("name", "subject")),
new XElement(ns + "field", new XAttribute("name", "content")),
new XElement(ns + "attr",
new XAttribute("name", "published"),
new XAttribute("type", "timestamp"))));
That produces:
<container xmlns:sphinx="http://url/for/sphinx">
<sphinx:docset>
<sphinx:schema />
<sphinx:field name="subject" />
<sphinx:field name="content" />
<sphinx:attr name="published" type="timestamp" />
</sphinx:docset>
</container>

You can read the namespace of your document and use it in queries like this:
XDocument xml = XDocument.Load(address);
XNamespace ns = xml.Root.Name.Namespace;
foreach (XElement el in xml.Descendants(ns + "whateverYourElementNameIs"))
//do stuff

How do I add multiple Namespace declarations to an XDocument?

I'm using an XDocument to build an Xml document in a known structure. The structure I am trying to build is as follows:
<request xmlns:ns4="http://www.example.com/a" xmlns:ns3="http://www.example.com/b" xmlns:ns2="http://www.example.com/c" >
<requestId>d78d4056-a831-4c7d-a357-d14402f623fc</requestId>
....
</request>
Notice the "xmlns:nsX" attributes.
I am trying, without success, to add these attributes to my "request" element.
XNamespace ns4 = XNamespace.Get("http://www.example.com/a");
XNamespace ns3 = XNamespace.Get("http://www.example.com/b");
XNamespace ns2 = XNamespace.Get("http://www.example.com/c");
XDocument doc = new XDocument(
new XDeclaration("1.0", "utf-8", "no"),
new XElement("request",
new XAttribute("ns4", ns4),
new XAttribute("ns3", ns3),
new XAttribute("ns2", ns2),
new XElement("requestId", Guid.NewGuid())
)
);
However, this produces the following:
<request ns4="http://www.example.com/a" ns3="http://www.example.com/b" ns2="http://www.example.com/c">
<requestId>38b07cfb-5e41-4d9a-97c8-4740c0432f11</requestId>
</request>
How do I add the namespace declarations correctly?

Do you mean:
new XAttribute(XNamespace.Xmlns + "ns4", ns4),
new XAttribute(XNamespace.Xmlns + "ns3", ns3),
new XAttribute(XNamespace.Xmlns + "ns2", ns2),