How to use XPath with XElement or LINQ?

Question

Consider the following XML:

<response>
  <status_code>200</status_code>
  <status_txt>OK</status_txt>
  <data>
    <url>http://bit.ly/b47LVi</url>
    <hash>b47LVi</hash>
    <global_hash>9EJa3m</global_hash>
    <long_url>http://www.tumblr.com/docs/en/api#api_write</long_url>
    <new_hash>0</new_hash>
  </data>
</response>

I'm looking for a really short way to get just the value of the <hash> element. I tried:

var hash = xml.Element("hash").Value;

But that's not working. Is it possible to provide an XPath query to an XElement? I can do it with the older System.Xml framework, doing something like:

xml.Node("/response/data/hash").Value

Is there something like this in a LINQ namespace?

---

UPDATE:

After monkeying around with this some more I found a way to do what I'm trying to do:

var hash = xml.Descendants("hash").FirstOrDefault().Value;

I'd still be interested to see if anyone has a better solution?

Pb

Don't use FirstOfDefault() in this case, because if "hash" is not found you will get a NullReferenceException. Use First() instead, you will get a more descriptive exception. – Corkboard

Use First() if you expect "hash" to always exists. Otherwise, FirstOrDefault() is fine as long as you check for null before access the Value property. – Scallion

Answer 1

To use XPath with LINQ to XML, add a using declaration for System.Xml.XPath; this will bring the extension methods of System.Xml.XPath.Extensions into scope.

In your example:

var value = (string)xml.XPathEvaluate("/response/data/hash");

Note that there are other methods provided by this class, such as XPathSelectElement() which returns an XElement?.

Brow

OK, seems closest to the original question – Soutane

Actually, it's (now?) in System.Xml.XPath. – Luana

@DanFriedman it hasn't moved. Note link is to class docs, slightly earlier I give the namespace (without a link). – Brow

Also note that you need to to add an assembly via NuGet for UWP apps: link – Chokecherry

I find it easier to use method XPathSelectElement and get back an XElement instead of an object. – Barefoot

Answer 2

Others have entirely reasonably suggested how to use "native" LINQ to XML queries to do what you want.

However, in the interests of providing lots of alternatives, consider XPathSelectElement, XPathSelectElements and XPathEvaluate to evaluate XPath expressions against an XNode (they're all extension methods on XNode). You can also use CreateNavigator to create an XPathNavigator for an XNode.

Personally I'm a big fan of using the LINQ to XML API directly, as I'm a big LINQ fan, but if you're more comfortable with XPath, the above may help you.

Winn

Answer 3

See, when dealing with LINQ to XML why dont you use LINQ to get the actual object.

Descendants find each element from the whole XML and lists all the objects that matches the name specified. So in your case hash is the name which it finds.

So, rather than doing

var hash = xml.Descendants("hash").FirstOrDefault().Value;

I would break apart like :

var elements = xml.Descendants("hash");
var hash = elements.FirstOrDefault();

if(hash != null)
 hash.Value // as hash can be null when default. 

In this way you might also get attributes, nodes elements etc.

Check this article to get clear idea about it so that it helps. http://www.codeproject.com/KB/linq/LINQtoXML.aspx I hope this will help you.

Palatial

@adhishek +1 for explaining the value of separating the element to it's own variable so you can do other stuff like get attributes, etc.. – Pb

One reason to use XPath is you lose all those things XPath can do and Linq can't. The first obvious one coming to mind is to execute a query which is defined at runtime (say an expression read from configuration or whatever). – Vacuum

Answer 4

You can use .Element() method to chain the elements to form XPath-like structure.

For your example:

XElement xml = XElement.Parse(@"...your xml...");
XElement hash = xml.Element("data").Element("hash");

Schematism

I think this is the best answer because it gets job done while continuing to use LINQ to XML (which is recommended) instead of using XPath with LINQ to XML query (which is not recommended). – Ovate

Using XPath is more concise especially if you are looking for any grand children or beyond. – Scallion

Element() can return null so this is unsafe. – Kealey

Answer 5

I have tried to come up with a LINQesq framework for generating xpath. It lets you describe xpath using c# lambda expressions

var xpath = CreateXpath.Where(e => e.TargetElementName == "td" && e.Parent.Name == "tr");

var xpath = CreateXpath.Where(e => e.TargetElementName == "td").Select(e => e.Text);

Not sure if this is helpful in this context, but you can find documentation here:

http://www.syntaxsuccess.com/viewarticle/how-to-create-xpath-using-linq

Fons

Answer 6

The answer is Yes & No. It is possible but not with XElement as Xelement doesn't represent the whole document but just a part of it. XDocument which represent the whole xml document has a function called XPathSelectElement() for this very purpose.

So for an Xml like

<response>
  <status_code>200</status_code>
  <status_txt>OK</status_txt>
  <data>
    <url>http://someurl/b47LVi</url>
    <hash>b47LVi</hash>
    <global_hash>9EJa3m</global_hash>
    <long_url>http://www.tumblr.com/docs/en/api#api_write</long_url>
    <new_hash>0</new_hash>
  </data>
</response>

You first need to read it as XDocument with

XDocument.Parse("xmlcontent..");

//convert from Xelement
var xe = XElement.Parse("xml string data...");
var xd = new XDocument(xe);

Then you can call XDocument.XPathSelectElement("/response/data/hash") to get your result as the Example below:

void Main()
{
    var xm = @"<response>
  <status_code>200</status_code>
  <status_txt>OK</status_txt>
  <data>
    <url>http://someurl/b47LVi</url>
    <hash>b47LVi</hash>
    <global_hash>9EJa3m</global_hash>
    <long_url>http://www.tumblr.com/docs/en/api#api_write</long_url>
    <new_hash>0</new_hash>
  </data>
</response>";
    
    var xd = XDocument.Parse(xm);
    xd.XPathSelectElement("/response/data/hash").Dump("element");
    xd.XPathSelectElement("/response/data/hash").Value.Dump("value");

}

Note: Dump() is a method to do Console.WriteLine() kindly replace in your end

And the output will come something like below:

Hackett