How to query XML based on element value

Question

I have an IEnumerable<XElement> object that I want to query based on a certain node value, but continually get a null element error. How do I select the value of two elements based on the value of a searched element? I am attempting to return firstName and lastName where ID == somevalue.

Here is the structure of my XML:

<Profile>
    <ID>123</ID>
    <firstName>Not</firstName>
    <lastName>Registered</lastName>
</Profile>

Snippet of my query:

XDocument xdoc = XDocument.Load(someXml);
IEnumerable<XElement> nodes = xdoc.Root.Elements();
XNamespace ns = "xmlNamespace";

var name = nodes.Elements(ns + "firstName")
     .Where(x => (int)x.Element(ns + "ID") == 123)
     .SingleOrDefault();

I was basing my query on this article, but I still can't find a mixture that returns what I want.

UPDATE

I have tried the suggested answers below and still see no results or receive an Object reference not set to an instance of an object exception.

I am still working through the issue and am now trying this:

var result = xdoc
    .Descendants(ns + "Profile")
    .Where(x => (int)x.Element(ns + "ID") == 1)
    .Select(x => new { FirstName = (string)x.Element(ns + "firstName"), LastName = (string)x.Element(ns + "lastName") })
    .FirstOrDefault();

When stepping through this, the query hangs after running the Where clause.

Answer 1

Your xml Like this

<?xml version="1.0" encoding="utf-8" ?>
<Employee>
  <Profile>
    <ID>123</ID>
    <firstName>Kumod</firstName>
    <lastName>Singh</lastName>
  </Profile>
  <Profile>
    <ID>124</ID>
    <firstName>Ravi</firstName>
    <lastName>Ranjam</lastName>
  </Profile>
</Employee>

We can access the first Name and Last Name

 string strPath1 = Server.MapPath("~/XmlData/abc.xml");
        var ResultOfFirLasName = (from studentProfile in XDocument.Load(strPath1).Descendants("Profile")
                                  where (int)studentProfile.Element("ID") == 123
                                  select new { FirstName = (string)studentProfile.Element("firstName"), LastName = (string)studentProfile.Element("lastName") }).FirstOrDefault();
        string strFirstName = ResultOfFirLasName.FirstName;
        string LastName = ResultOfFirLasName.LastName;

You can do with lemda expression too

var ResultOfFirLasName1 = XDocument.Load(strPath1).Descendants("Profile").Where(x => (int)x.Element("ID") == 123).Select(x=> new {FirstName =(string)x.Element("firstName"),LastName =(string)x.Element("lastName")}).FirstOrDefault();

Same way you again access the first Name and Last Name

Answer 2

I do this examples to deal with namespace:

Profiles.xml:

<Profiles xmlns="http://schemas.microsoft.com/2004/06/E2ETraceEvent">
    <Profile>
        <ID>122</ID>
        <firstName>Not</firstName>
        <lastName>Registered</lastName>
    </Profile>
    <Profile>   
        <ID>123</ID>
        <firstName>Not</firstName>
        <lastName>Registered</lastName>
    </Profile>
</Profiles>

Code:

XElement xDoc = XElement.Load(@"C:\Profiles.xml");
XNamespace ns = "http://schemas.microsoft.com/2004/06/E2ETraceEvent";

var profile = xDoc.Elements(ns + "Profile")
            .SingleOrDefault(x => x.Element(ns + "ID").Value == "123");
Console.WriteLine("firstName: " + profile.Element(ns + "firstName").Value);
Console.WriteLine("lastName: " + profile.Element(ns + "lastName").Value);

Hope this help.

Answer 3

I suppose "Profile" is not a root of your XML after all.

So if I am reading your mind correctly you have something like this:

Xml:

<root>
<Profile>
    <ID>123</ID>
    <firstName>Not</firstName>
    <lastName>Registered</lastName>
</Profile>
<Profile>
    <ID>124</ID>
    <firstName>A</firstName>
    <lastName>B</lastName>
</Profile>
</root>

Code to get profile section where id element equals to 123:

var result = XDocument.Parse(yourXml)
        .Root
        .Elements()
        .SingleOrDefault(i => i.Element("ID").Value == "123");