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c# LINQ how to determin a XElement with specific attribute

i would like to realize this functionality:
determin, whether the XML file has a XElement with specific attribute or not.
This is the example XML code:
<root>
<pou objectId="name">
</pou>
<pou objectId="value">
</pou>
<pou objectId="address">
</pou>
</root>
I would like to determin, whether the XML file has a specific XElement "pou" with attribute ObjectId "name" or not.
The following is my code in C# using Descendants
XDocument xdoc = XDocument.Load(#"C:\Users\jsc\Desktop\TestForInherit.xml");
XDocument xNew = new XDocument();
xNew.Add(new XElement("root"));
if (xdoc.Descendants("pou").Where(x=> (string)x.Attribute("objectId") =="name").Any()==true)
{
xNew.Add(new XElement("pou", new XAttribute("objectId", "name")));
}
xNew.Save(#"C:\Users\jsc\Desktop\TestForInheritNew.xml");
If the xml file has the XElement with specific attribute value, then add thie XElement to the new XML file.
But unfortunatelly it does not work. Can anyone give me some advise.

Please try the following syntax to check if there's an attribute with specific name:
xdoc.Descendants("pou").Where(x=> x.Attribute("objectId") != null)

write xml prefix c#

I am trying to create an xml in c# and specifying the namespace and then the prefix on each element.
<bk:library xmlns:bk="www.namespace.com/ww">
<bk:books>
<bk:book>
<bk:title>Title </bk:book>
</bk:book>
<bk:books>
</bk:library>
I have done the following code:
XmlDocument doc = new XmlDocument();
root = doc.AppendChild(doc.CreateElement("library"));
var booksNode = root.appendChild(doc.CreateElement("bk","books","www.namespace.com/ww"));
Console.WriteLine(doc.OuterXml);
I get something like this:
<bk:books xmlns:bk="www.namespace.com/ww">
So it outputs both the prefix and the namespace
It doesn't output the xml as I would like it (shown above).
Any idea how I can get the xml to be output like I have shown?
thanks

Try this
XmlDocument doc = new XmlDocument();
XmlElement root = (XmlElement)doc.AppendChild(doc.CreateElement("bk","library","www.namespace.com/ww"));
var booksNode = root.AppendChild(doc.CreateElement("bk", "books", "www.namespace.com/ww"));
Console.WriteLine(doc.OuterXml);

How to get value of a specific element in xml in c#

I have a xml file in below format
I want to fetch the value of Child1
When I am using below code it is providing a null value. Please help
XDocument xmlDoc = XDocument.Load(fileName);
XElement po = xmlDoc.Root.Element("Root");
XElement el1 = po.Element("Child1");

Use this:
xmlDoc.Descendants("Child1").First();

Read first root node from XML

I work with three kinds of XML files :
Type A:
<?xml version="1.0" encoding="UTF-8"?>
<nfeProc versao="2.00" xmlns="http://www.portalfiscal.inf.br/nfe">
</nfeProc>
Tyepe B:
<?xml version="1.0" encoding="UTF-8"?>
<cancCTe xmlns="http://www.portalfiscal.inf.br/cte" versao="1.04">
</cancCTe>
Type C:]
<?xml version="1.0" encoding="UTF-8"?>
<cteProc xmlns="http://www.portalfiscal.inf.br/cte" versao="1.04">
</cteProc>
I have try with this code to read the first node :
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(#"C:\crruopto\135120068964590_v01.04-procCTe.xml");
XmlNodeList ml = xmlDoc.GetElementsByTagName("*");
XmlElement root = xmlDoc.DocumentElement;
exti = root.ToString();
but dont return anything i want to read the first node , need to know if the file is nfeProc ,canCTE or cteProc
The second question is how i get the value from "value" in the same tag???
Thanks

From this post:
//Root node is the DocumentElement property of XmlDocument
XmlElement root = xmlDoc.DocumentElement
//If you only have the node, you can get the root node by
XmlElement root = xmlNode.OwnerDocument.DocumentElement

I would suggest using XPath. Here's an example where I read in the XML content from a locally stored string and select whatever the first node under the root is:
XmlDocument doc = new XmlDocument();
doc.Load(new StringReader(xml));
XmlNode node = doc.SelectSingleNode("(/*)");

If you aren't required to use the XmlDocument stuff, then Linq is your friend.
XDocument doc = XDocument.Load(#"C:\crruopto\135120068964590_v01.04-procCTe.xml");
XElement first = doc.GetDescendants().FirstOrDefault();
if(first != null)
{
//first.Name will be either nfeProc, canCTE or cteProc.
}

Working with Linq to XML is the newest and most powerful way of working with XML in .NET and offers you a lot more power and flexibility than things like XmlDocument and XmlNode.
Getting the root node is very simple:
XDocument doc = XDocument.Load(#"C:\crruopto\135120068964590_v01.04-procCTe.xml");
Console.WriteLine(doc.Root.Name.ToString());
Once you have constructed an XDocument you don't need to use any LINQ querying or special checking. You simply pull the Root property from the XDocument.

Thanks i have solved this way the first part
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(nomear);
XmlNodeList ml = xmlDoc.GetElementsByTagName("*");
XmlNode primer = xmlDoc.DocumentElement;
exti = primer.Name;

First, to be clear, you're asking about the root element, not the root node.
You can use an XmlReader to avoid having to load large documents completely into memory. See my answer to a how to find the root element at https://stackoverflow.com/a/60642354/1307074.
Second, once the reader is referencing the element, you can use the reader's Name property to get the qualified tag name of the element. You can get the value as a string using the Value property.

Selecting XML nodes?

I have a large XML file with a lot of these file nodes:
<File>
<Component>Main</Component>
<Path>C:\Logs\Main</Path>
<FileName>logfile1.log</FileName>
</File>
In my C# program I want to select a node with a certain file name, eg in the above example I would like to select the File node where the FileName is logfile1.log. Is there a way I can do this in my C#, or maybe I need to make the FileName as an attribute for each File node, e.g.:
<File name="logfile1.log">...</File>
Could anybody advise me on the best practise here? Thanks for any help!

Using query syntax;
var xml = XDocument.Load("input.xml");
var node = (from file in xml.Descendants("File")
where (string)file.Element("FileName") == "logfile1.log"
select file).Single();
Obviously the call to force the query (Single() in this case) should be swapped out to suit your own app.

XPath query would be a good choice for that. You can use xpath to search for either an element name or an attribute name.
something like:
var doc = new XPathDocument(path);
var xpath = doc.CreateNavigator();
//with element
var node = xpath.SelectSingleNode("//File[FileName='logfile1.log']");
//or with attribute
var node = xpath.SelectSingleNode("//File[#name='logfile1.log']");
Or, if there could be more than one you can use Select to find multiple matches and then iterate them.
var node = xpath.Select("//File...");

var doc = new XmlDocument();
doc.LoadXml(xml); // or Load(path)
var node = doc.SelectSingleNode("//File/FileName[.='logfile1.log']");
(see XPath selection by innertext)
or
var doc = XDocument.Load(path);
var node = doc.Elements("Path").FirstOrDefault(e => (string)e.Element("FileName") == "logfile1.log");