CODEWITHSUNDEEP
.netxmlxpathlinq-to-xmlxelement
Paul Fryer
Paul Fryer

Reputation: 9537

How to use XPath with XElement or LINQ?

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?

Upvotes: 84

Views: 69592

Answers (6)

Richard
Richard

Reputation: 109180

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?.

Upvotes: 149

Vinod Srivastav
Vinod Srivastav

Reputation: 4263

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: enter image description here

Upvotes: 1

TGH
TGH

Reputation: 39278

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

Upvotes: 3

panpawel
panpawel

Reputation: 1848

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");

Upvotes: 9

abhishek
abhishek

Reputation: 2992

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.

Upvotes: 14

Jon Skeet
Jon Skeet

Reputation: 1503759

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.

Upvotes: 41

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