I have an XDocument
object. I want to query for elements with a particular name at any depth using LINQ.
When I use Descendants("element_name")
, I only get elements that are direct children of the current level. I'm looking for the equivalent of "//element_name" in XPath...should I just use XPath
, or is there a way to do it using LINQ methods?
This question is related to
c#
.net
xml
linq
linq-to-xml
Following @Francisco Goldenstein answer, I wrote an extension method
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
namespace Mediatel.Framework
{
public static class XDocumentHelper
{
public static IEnumerable<XElement> DescendantElements(this XDocument xDocument, string nodeName)
{
return xDocument.Descendants().Where(p => p.Name.LocalName == nodeName);
}
}
}
There are two ways to accomplish this,
The following are samples of using these approaches,
List<XElement> result = doc.Root.Element("emails").Elements("emailAddress").ToList();
If you use XPath, you need to do some manipulation with the IEnumerable:
IEnumerable<XElement> mails = ((IEnumerable)doc.XPathEvaluate("/emails/emailAddress")).Cast<XElement>();
Note that
var res = doc.XPathEvaluate("/emails/emailAddress");
results either a null pointer, or no results.
This my variant of the solution based on LINQ and the Descendants method of the XDocument
class
using System;
using System.Linq;
using System.Xml.Linq;
class Test
{
static void Main()
{
XDocument xml = XDocument.Parse(@"
<root>
<child id='1'/>
<child id='2'>
<subChild id='3'>
<extChild id='5' />
<extChild id='6' />
</subChild>
<subChild id='4'>
<extChild id='7' />
</subChild>
</child>
</root>");
xml.Descendants().Where(p => p.Name.LocalName == "extChild")
.ToList()
.ForEach(e => Console.WriteLine(e));
Console.ReadLine();
}
}
We know the above is true. Jon is never wrong; real life wishes can go a little further.
<ota:OTA_AirAvailRQ
xmlns:ota="http://www.opentravel.org/OTA/2003/05" EchoToken="740" Target=" Test" TimeStamp="2012-07-19T14:42:55.198Z" Version="1.1">
<ota:OriginDestinationInformation>
<ota:DepartureDateTime>2012-07-20T00:00:00Z</ota:DepartureDateTime>
</ota:OriginDestinationInformation>
</ota:OTA_AirAvailRQ>
For example, usually the problem is, how can we get EchoToken in the above XML document? Or how to blur the element with the name attribute.
You can find them by accessing with the namespace and the name like below
doc.Descendants().Where(p => p.Name.LocalName == "OTA_AirAvailRQ").Attributes("EchoToken").FirstOrDefault().Value
You can find it by the attribute content value, like this one.
I am using XPathSelectElements
extension method which works in the same way to XmlDocument.SelectNodes
method:
using System;
using System.Xml.Linq;
using System.Xml.XPath; // for XPathSelectElements
namespace testconsoleApp
{
class Program
{
static void Main(string[] args)
{
XDocument xdoc = XDocument.Parse(
@"<root>
<child>
<name>john</name>
</child>
<child>
<name>fred</name>
</child>
<child>
<name>mark</name>
</child>
</root>");
foreach (var childElem in xdoc.XPathSelectElements("//child"))
{
string childName = childElem.Element("name").Value;
Console.WriteLine(childName);
}
}
}
}
Descendants will do exactly what you need, but be sure that you have included a namespace name together with element's name. If you omit it, you will probably get an empty list.
(Code and Instructions is for C# and may need to be slightly altered for other languages)
This example works perfect if you want to read from a Parent Node that has many children, for example look at the following XML;
<?xml version="1.0" encoding="UTF-8"?>
<emails>
<emailAddress>[email protected]</emailAddress>
<emailAddress>[email protected]</emailAddress>
<emailAddress>rgreen@set_ig.ca</emailAddress>
</emails>
Now with this code below (keeping in mind that the XML File is stored in resources (See the links at end of snippet for help on resources) You can obtain each email address within the "emails" tag.
XDocument doc = XDocument.Parse(Properties.Resources.EmailAddresses);
var emailAddresses = (from emails in doc.Descendants("emailAddress")
select emails.Value);
foreach (var email in emailAddresses)
{
//Comment out if using WPF or Windows Form project
Console.WriteLine(email.ToString());
//Remove comment if using WPF or Windows Form project
//MessageBox.Show(email.ToString());
}
Note: For Console Application and WPF or Windows Forms you must add the "using System.Xml.Linq;" Using directive at the top of your project, for Console you will also need to add a reference to this namespace before adding the Using directive. Also for Console there will be no Resource file by default under the "Properties folder" so you have to manually add the Resource file. The MSDN articles below, explain this in detail.
An example indicating the namespace:
String TheDocumentContent =
@"
<TheNamespace:root xmlns:TheNamespace = 'http://www.w3.org/2001/XMLSchema' >
<TheNamespace:GrandParent>
<TheNamespace:Parent>
<TheNamespace:Child theName = 'Fred' />
<TheNamespace:Child theName = 'Gabi' />
<TheNamespace:Child theName = 'George'/>
<TheNamespace:Child theName = 'Grace' />
<TheNamespace:Child theName = 'Sam' />
</TheNamespace:Parent>
</TheNamespace:GrandParent>
</TheNamespace:root>
";
XDocument TheDocument = XDocument.Parse( TheDocumentContent );
//Example 1:
var TheElements1 =
from
AnyElement
in
TheDocument.Descendants( "{http://www.w3.org/2001/XMLSchema}Child" )
select
AnyElement;
ResultsTxt.AppendText( TheElements1.Count().ToString() );
//Example 2:
var TheElements2 =
from
AnyElement
in
TheDocument.Descendants( "{http://www.w3.org/2001/XMLSchema}Child" )
where
AnyElement.Attribute( "theName" ).Value.StartsWith( "G" )
select
AnyElement;
foreach ( XElement CurrentElement in TheElements2 )
{
ResultsTxt.AppendText( "\r\n" + CurrentElement.Attribute( "theName" ).Value );
}
You can do it this way:
xml.Descendants().Where(p => p.Name.LocalName == "Name of the node to find")
where xml
is a XDocument
.
Be aware that the property Name
returns an object that has a LocalName
and a Namespace
. That's why you have to use Name.LocalName
if you want to compare by name.
Source: Stackoverflow.com