We Keep Coding

How to select a single XML node in c# using multiple XPath queries

I'm trying to select a single node from an XML file based on two queries, I have a product ID for which I need the latest entry - highest issue number.
This is the format of my XML file:
<MyProducts>
<Product code="1011234">
<ProductName>Product Name A</ProductName>
<ProductId>101</ProductId>
<IssueNumber>1234</IssueNumber>
</Product>
<Product code="1029999">
<ProductName>Product Name B</ProductName>
<ProductId>102</ProductId>
<IssueNumber>9999</IssueNumber>
</Product>
<Product code="1015678">
<ProductName>Product Name A2</ProductName>
<ProductId>101</ProductId>
<IssueNumber>5678</IssueNumber>
</Product>
</MyProducts>
I need to get the <product> node from a ProductId that has the highest IssueNumber. For example if the ProductId is 101 I want the third node, if it's 102, I want the second node. There are around 50 different products in the file, split over three different product ids.
I've tried a number of XPath combinations using SelectSingleNode either by using the specific ProductID and IssueNumber nodes, or by using the code attribute of the product node (which is a combination of Id and Issue) without any success.
The code currently uses the code attribute, but only because we're also passing in the issue number and I want to be able to do this without the issue number (to decrease front end maintenance) as it's always the highest issue we want.
Current code is this:
XmlNode productNode = productXml.SelectSingleNode("/MyProducts/Product[#code='" + productCode + "']");
I've used these as well, they kind of work, but select the inner nodes, not the outer Product node:
XmlNodeList productNodes = productXml.SelectNodes("/MyProducts/Product/ProductId[text()='101']");
XmlNodeList productNodes = productXml.SelectNodes("/MyProducts/Product[not (../Product/IssueNumber > IssueNumber)]/IssueNumber");
I would like to use a combination of the two, something like this:
XmlNode productNode = productXml.SelectSingleNode("/MyProducts/Product/ProductId[text()='101'] and /MyProducts/Product[not (../Product/IssueNumber > IssueNumber)]/IssueNumber");
But that returns the error "...threw an exception of type 'System.Xml.XPath.XPathException'", but I also expect it won't return the Product node anyway.
Can this even be done in a single line, or will I have to loop through the nodes to find the right one?

Use Xml Linq
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;
namespace ConsoleApplication167
{
class Program
{
const string FILENAME = #"c:\temp\test.xml";
static void Main(string[] args)
{
XDocument doc = XDocument.Load(FILENAME);
var products = doc.Descendants("Product")
.OrderByDescending(x => (int)x.Element("IssueNumber"))
.GroupBy(x => (int)x.Element("ProductId"))
.Select(x => x.First())
.ToList();
Dictionary<int, XElement> dict = products
.GroupBy(x => (int)x.Element("ProductId"), y => y)
.ToDictionary(x => x.Key, y => y.FirstOrDefault());
XElement highestId = dict[101];
}
}
}

Your last idea is almost there. You need to put the two clauses inside the [] selector. There is also max() available which I think clarifies the logic. This should work:
/MyProducts/Product[ProductId='101'
and IssueNumber=max(/MyProducts/Product[ProductId='101']/IssueNumber)]
This selects the Product which both has id 101 and has the highest IssueNumber of all id-101-products.

Get a name attribute values from multiple inner elements od XML File into C#

In following code I want to get the name attribute value of all the inner elements of <List> which are <InnerList>.
The requirement is to store the attribute name values to the array in c# code.
<List>
<InnerList name="abc">
<element1></element1>
<element2></element2>
</InnerList>
<InnerList name="xyz">
<element1></element1>
<element2></element2>
</InnerList >
</List>
The required output is:
output = abc, xyz
The Output variable should contain the values of name attribute of all <InnerList> elements is array format which can be displayed via foreach loop.

You can try using XDocument
var xdoc = XDocument.Load(fileName);
var result = string.Join(", ", xdoc.Descendants("InnerList")
.Select(x => x.Attribute("name").Value));

Retrieving specific data from XML file

Using LINQ to XML.
I have an XML file which looks like this:
<?xml version="1.0" encoding="utf-8"?>
<TileMap xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Title>title</Title>
<Abstract>Some clever text about this.</Abstract>
<SRS>OSGEO:41001</SRS>
<Profile>global-mercator or something</Profile>
</TileMap>
I can retrieve the <Title> from this with no problems by using this little piece of code:
string xmlString = AppDomain.CurrentDomain.BaseDirectory + #"Capabilities\" + name + ".xml";
string xmlText = File.ReadAllText(xmlString);
byte[] buffer = Encoding.UTF8.GetBytes(xmlText);
XElement element = XElement.Load(xmlString);
IEnumerable<XElement> title =
from el in element.Elements("Title")
select el;
foreach (XElement el in title)
{
var elementValue = el.Value;
}
However, this isn't very flexible because say I have an XML file that looks like this:
<?xml version="1.0" encoding="utf-8"?>
<RootObject xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Services>
<TileMapService>
<Title>title</Title>
<href>http://localhost/root</href>
</TileMapService>
</Services>
</RootObject>
It can't find <Title> but it finds <Services> (I presume) but since it's not called "Title" it just ignores it. I'm not very strong in working with XML. How would I go about making a method that looks through the XML and fetches me "Title" or however you'd implement this?

You're currently just looking at the child elements of the root element.
Instead, if you want to find all descendants, use Descendants.
Additionally, there's no point in using a query expression of from x in y select x (or rather, there's a very limited point in some cases, but not here). So just use:
var titles = element.Descendants("Title");
Personally I would actually use XDocument here rather than XElement - you have after all got a whole document, complete with XML declaration, not just an element.

Change your LINQ query to:
IEnumerable<XElement> title =
from el in element.Descendants("Title")
select el;
Elements returns only the immediate children, Descendants returns all descendant nodes instead.

Descendants will select all the "Title" elements irrespective of the level. Please use xpath to correctly locate the element
using System;
using System.Linq;
using System.Xml.Linq;
using System.Xml.XPath;
using System.IO;
public class Program
{
public static void Main()
{
string xmlFile = AppDomain.CurrentDomain.BaseDirectory + #"Capabilities\" + name + ".xml";
XElement xml=XElement.Load(xmlFile);
IEnumerable<XElement> titleElements = xml.XPathSelectElements("//Services/TileMapService/Title");
}
}

access xml element by attribute value

Probably this question repeated, but i am not satiesfied with existing answers. I want to get xml element from dynamically generated xml file by attribute value. we don't know how many nodes, and its herarchy. but each element, its sub element, its sub-sub elements, sub-sub-sub elements...so on will contain unique guid as "Id" attribute :
<Element id="">
<SubElement id=""></SubElement>
<SubElement id="">
<SubSubElement id="">
<SubSubSubElement id="">
<SubSubSubSubElement id="">....other sub inside this ...</SubSubSubSubElement>
</SubSubSubElement>
</SubSubElement>
</SubElement>
</Element>
I want to find the element by only passing the Guid value. nonethless of its xpath, its node location / position. how can i do this in C#? is i need to use LINQ?
Edited:
XDocument xmldoc = XDocument.Load(xmlFilePath);
XElement selectedElement = xmldoc.Descendants().Where(x => (string) x.Attribute("id") == myIdvalue).FirstOrDefault();
Exception :
"Expression cannot contain lambda expressions"
I have added Using System.Linq namspaces.

hoipolloi has given an XPath answer, which is fine - but I would personally use LINQ to XML. (See my blog post on code and data for reasons.)
var element = parent.Descendants()
.Where(x => (Guid?) x.Attribute("id") == id)
.FirstOrDefault();
This will perform appropriate GUID parsing on each id attribute (returning a "null" Guid? value for non-GUIDs). If you're certain of the text format of your ID, you can cast to string instead:
var element = parent.Descendants()
.Where(x => (string) x.Attribute("id") == idText)
.FirstOrDefault();
Change the FirstOrDefault to Single, SingleOrDefault or First depending on your requirements.
EDIT: It's not at all clear what's going wrong with the code you've posted. Here's a short but complete program which shows it working fine. Please compare this with your code:
using System;
using System.Linq;
using System.Xml.Linq;
class Test
{
static void Main()
{
string xml = "<parent><foo id='bar' /><foo id='baz' /></parent>";
XDocument doc = XDocument.Parse(xml);
string idToFind = "bar";
XElement selectedElement = doc.Descendants()
.Where(x => (string) x.Attribute("id") == idToFind).FirstOrDefault();
Console.WriteLine(selectedElement);
}
}

You can use XPath to do this. For instance, the following matches all elements with an id of 'foo', irrespective of their location in the document:
//*[#id='foo']

Query an XDocument for elements by name at any depth

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?

Descendants should work absolutely fine. Here's an example:
using System;
using System.Xml.Linq;
class Test
{
static void Main()
{
string xml = #"
<root>
<child id='1'/>
<child id='2'>
<grandchild id='3' />
<grandchild id='4' />
</child>
</root>";
XDocument doc = XDocument.Parse(xml);
foreach (XElement element in doc.Descendants("grandchild"))
{
Console.WriteLine(element);
}
}
}
Results:
<grandchild id="3" />
<grandchild id="4" />

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.

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.

There are two ways to accomplish this,
LINQ to XML
XPath
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.

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);
}
}
}
}

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);
}
}
}

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();
}
}
Results:
For more details on the Desendants method take a look here.

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.

(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>jdoe#set.ca</emailAddress>
<emailAddress>jsmith#hit.ca</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());
}
Results
jdoe#set.ca
jsmith#hit.ca
rgreen#set_ig.ca
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.
Adding and Editing Resources
How to: Add or Remove Resources