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Linq to XML elements

Hi I try to read an xml file with LINQ.
The name of the file is:categorizedBooks.xml
and the content of the file looks like this:
<category name=".NET">
<books>
<book>CLR via C#</book>
<book>Essential .NET</book>
</books>
</category>
The code for reading the file looks like this:
XElement rootss = XElement.Load(#"D:/categorizedBooks.xml");
XElement dotNetCategoryss = rootss.Element("category");
XAttribute namehallo = dotNetCategoryss.Attribute("name");
XElement booksss = dotNetCategoryss.Element("books");
IEnumerable<XElement> bookElements = booksss.Elements("book");
Console.WriteLine((string)dotNetCategoryss);
foreach (XElement bookElement in bookElements)
{
Console.WriteLine(" - " + (string)bookElement);
}
But i get null on this line:
XAttribute namehallo = dotNetCategoryss.Attribute("name");
So how to fix this , so that it not will be null?
Thank you

Your doc root is the category element - try:
XAttribute namehallo = rootss.Attribute("name");
Console.WriteLine(namehallo.Value);
You'll have to change your other XElement references similarly

instead of XElement.Load use XDocument.Load or XDocument.Parse
var xml = #"
<category name='.NET'>
<books>
<book>CLR via C#</book>
<book>Essential .NET</book>
</books>
</category>";
var document = XDocument.Parse(xml);
// returns: .NET
var category = document
.Element("category")
.Attributes("name")
.Select(p => p.Value);
// returns: CLR via C#, Essential .NET
var books = document
.Descendants("book")
.Select(p => p.Value);

Adding an element to this xml structure

<root>
<element1>innertext</element1>
<element2>innertext</element2>
<element3>
<child1>innertext</child1>
</element3>
</root>
I have an xml structure shown above.
I would like to "append" the xml file (it is already created) to add another "child" inside element3>, so that it will look like this:
<root>
<element1>innertext</element1>
<element2>innertext</element2>
<element3>
<child1>innertext</child1>
<child2>innertext</child2>
</element3>
</root>
Linq to xml and/or Xpath would be great
EDIT:
I have tried doing this:
XElement doc = XElement.Load(mainDirectory);
XElement newElem = doc.Elements("element3").First();
newElem.Add(new XElement("child2", "child2innertext"));
doc.Add(newElem);
doc.Save(mainDirectory);

XmlDocument xDoc = new XmlDocument();
xDoc.Load("filename.xml");
foreach (XmlNode xNode in xDoc.SelectNodes("/root/element3"))
{
XmlElement newElement = xDoc.CreateElement("Child2");
xNode.AppendChild(newElement);
xNode.InnerText = "myInnerText";
}

With XDocument you can achieve this as:
string xml = "<root><element1>innertext</element1><element2>innertext</element2><element3><child1>innertext</child1></element3></root>";
var doc = XDocument.Parse(xml); //use XDocument.Load("filepath"); in case if your xml is in a file.
var el3 = doc.Descendants("element3").FirstOrDefault();
el3.Add(new XElement("child2", "innertext"));

Please, try this LINQPAD example
void Main()
{
var xml =
#"<root>
<element1>innertext</element1>
<element2>innertext</element2>
<element3>
<child1>innertext</child1>
</element3>
</root>";
var doc = XDocument.Parse(xml);
doc.Root.Element("element3")
.Add(new XElement("child2", "innertext"));
doc.Dump();
}

reading node from xml file in XMLDocument

i am trying to grab the TopicName how should i go after it and try different combination but somehow i am unable to get TopicName below is my source codee...
XmlDocument xdoc = new XmlDocument();//xml doc used for xml parsing
xdoc.Load(
"http://latestpackagingnews.blogspot.com/feeds/posts/default"
);//loading XML in xml doc
XmlNodeList xNodelst = xdoc.DocumentElement.SelectNodes("content");//reading node so that we can traverse thorugh the XML
foreach (XmlNode xNode in xNodelst)//traversing XML
{
//litFeed.Text += "read";
}
sample xml file
<content type="application/xml">
<CatalogItems xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="sitename.xsd">
<CatalogSource Acronym="ABC" OrganizationName="ABC Corporation" />
<CatalogItem Id="3212" CatalogUrl="urlname">
<ContentItem xmlns:content="sitename.xsd" TargetUrl="url">
<content:SelectionSpec ClassList="" ElementList="" />
<content:Language Value="eng" Scheme="ISO 639-2" />
<content:Source Acronym="ABC" OrganizationName="ABC Corporation" />
<content:Topics Scheme="ABC">
<content:Topic TopicName="Marketing" />
<content:Topic TopiccName="Coverage" />
</content:Topics>
</ContentItem>
</CatalogItem>
</CatalogItems>
</content>

The Topic nodes in your XML are using the content namespace - you need to declare and use the XML namespace in your code, then you can use SelectNodes() to grab the nodes of interest - this worked for me:
XmlNamespaceManager nsmgr = new XmlNamespaceManager(xdoc.NameTable);
nsmgr.AddNamespace("content", "sitename.xsd");
var topicNodes = xdoc.SelectNodes("//content:Topic", nsmgr);
foreach (XmlNode node in topicNodes)
{
string topic = node.Attributes["TopicName"].Value;
}
Just as a comparison see how easy this would be with Linq to XML:
XDocument xdoc = XDocument.Load("test.xml");
XNamespace ns = "sitename.xsd";
string topic = xdoc.Descendants(ns + "Topic")
.Select(x => (string)x.Attribute("TopicName"))
.FirstOrDefault();
To get all topics you can replace the last statement with:
var topics = xdoc.Descendants(ns + "Topic")
.Select(x => (string)x.Attribute("TopicName"))
.ToList();

If you just need a specific element, then I'd use XPath:
This is a guide to use XPath in C#:
http://www.codeproject.com/KB/XML/usingXPathNavigator.aspx
And this is the query that will get you a collection of your Topics:
//content/CatalogItems/CatalogItem/ContentItem/content:Topics/content:Topic
You could tweak this query depending on what it is you're trying to accomplish, grabbing just a specific TopicName value:
//content/CatalogItems/CatalogItem/ContentItem/content:Topics/content:Topic/#TopicName
XPath is pretty easy to learn. I've done stuff like this pretty quickly with no prior knowledge.
You can paste you XML and xpath query here to test your queries:
http://www.bit-101.com/xpath/

The following quick and dirty LINQ to XML code obtains your TopicNames and prints them on the console.
XDocument lDoc = XDocument.Load(lXmlDocUri);
foreach (var lElement in lDoc.Element("content").Element(XName.Get("CatalogItems", "sitename.xsd")).Elements(XName.Get("CatalogItem", "sitename.xsd")))
{
foreach (var lContentTopic in lElement.Element(XName.Get("ContentItem", "sitename.xsd")).Element(XName.Get("Topics", "sitename.xsd")).Elements(XName.Get("Topic", "sitename.xsd")))
{
string lTitle = lContentTopic.Attribute("TopicName").Value;
Console.WriteLine(lTitle);
}
}
It'd have been a lot shorter if it wasn't for all the namespaces :) (Instead of "XName.Get" you would just use the name of the element).

How to get the value of an XML attribute?

I have a XML file:
<SourceMessage xmlns="test.test">
<updated>2011</updated>
<title type="p1"/>
<title type="p2"/>
<title type="p3"/>
<entry>
</entry>
</SourceMessage>
How could I use LINQ to get the <type> attribute of the <title> element, i.e. "p1", "p2" and "p3"?

Use XDocument.Load or XDocument.Parse to load the XML data into an XDocument. Then, using LINQ, you can get the type for each <title> element under the document root as follows:
XNamespace test = "test.test";
XDocument doc = XDocument.Load(file);
// - or -
XDocument doc = XDocument.Parse("<SourceMessage ...");
IEnumerable<string> query = from title in doc.Root.Elements(test + "title")
select (string)title.Attribute("type");
foreach (string item in query)
{
Console.WriteLine(item);
}
Output:
p1
p2
p3

var xElement XElement.Parse(xmlString);
var result = xElement.Descendants("title")
.Select(e => e.Attribute("type").Value);

XDocument xml = XDocument.Parse (#"<SourceMessage xmlns="test.test">
<updated>2011</updated>
<title type="p1"/>
<title type="p2"/>
<title type="p3"/>
<entry>
</entry>
</SourceMessage>");
foreach (var t in xml.Root.Descendants("title"))
Console.Write(t.Attribute("type").Value);

Filter XDocument more efficiently

I would like to filter with high performance XML elements from an XML document.
Take for instance this XML file with contacts:
<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/xsl" href="asistentes.xslt"?>
<contactlist evento="Cena Navidad 2010" empresa="company">
<contact type="1" id="1">
<name>Name1</name>
<email>xxxx#zzzz.es</email>
<confirmado>SI</confirmado>
</contact>
<contact type="1" id="2">
<name>Name2</name>
<email>xxxxxxxxx#zzzze.es</email>
<confirmado>Sin confirmar</confirmado>
</contact>
</contaclist>
My current code to filter from this XML document:
using System;
using System.Xml.Linq;
class Test
{
static void Main()
{
string xml = #" the xml above";
XDocument doc = XDocument.Parse(xml);
foreach (XElement element in doc.Descendants("contact")) {
Console.WriteLine(element);
var id = element.Attribute("id").Value;
var valor = element.Descendants("confirmado").ToList()[0].Value;
var email = element.Descendants("email").ToList()[0].Value;
var name = element.Descendants("name").ToList()[0].Value;
if (valor.ToString() == "SI") { }
}
}
}
What would be the best way to optimize this code to filter on <confirmado> element content?

var doc = XDocument.Parse(xml);
var query = from contact in doc.Root.Elements("contact")
let confirmado = (string)contact.Element("confirmado")
where confirmado == "SI"
select new
{
Id = (int)contact.Attribute("id"),
Name = (string)contact.Element("name"),
Email = (string)contact.Element("email"),
Valor = confirmado
};
foreach (var contact in query)
{
...
}
Points of interest:
doc.Root.Elements("contact") selects only the <contact> elements in the document root, instead of searching the whole document for <contact> elements.
The XElement.Element method returns the first child element with the given name. No need to convert the child elements to a list and take the first element.
The XElement and XAttribute classes provide a wide selection of convenient conversion operators.

You could use LINQ:
foreach (XElement element in doc.Descendants("contact").Where(c => c.Element("confirmado").Value == "SI"))