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Parsing an UN XML file in C#

I'm trying to parse an XML file from UN website (http://www.un.org/sc/committees/1267/AQList.xml) using c#.
There is one problem I'm constantly having with this file, and that's the number of child tags varies from one <.INDIVIDUAL.> tag to another. One example is <.FORTH_NAME.> child tag.
I've tried a number of different approaches, but somehow I always seem to be stuck with the same problem, and that's different number of child tags inside <.INDIVIDUAL.> tag.
What I'm trying to achieve is to collect all the tags and their values under one <.INDIVIDUAL.> tag, and then insert only those I want into my database. If a tag is missing, for example <.FOURTH_NAME.>, than I need to insert only first three names into the database, and skip the fourth.
I've tried using Linq to XML, and here are some examples:
XDocument xdoc = XDocument.Load(path);
var tags = (from t in xdoc.Descendants("INDIVIDUALS")
from a in t.Elements("INDIVIDUAL")
select new
{
Tag = a.Name,
val = a.Value
});
foreach (var obj in tags)
{
Console.WriteLine(obj.Tag + " - " + obj.val + "\t");
//insert SQL goes here
}
or:
but this one only collects non empty FOURTH_NAME tags...
var q = (from c in xdoc.Descendants("INDIVIDUAL")
from _1 in c.Elements("FIRST_NAME")
from _2 in c.Elements("SECOND_NAME")
from _3 in c.Elements("THIRD_NAME")
from _4 in c.Elements("FOURTH_NAME")
where _1 != null && _2 != null && _3 != null && _4 != null
select new
{
_1 = c.Element("FIRST_NAME").Value,
_2 = c.Element("SECOND_NAME").Value,
_3 = c.Element("THIRD_NAME").Value,
_4 = c.Element("FOURTH_NAME").Value
});
foreach (var obj in q)
{
Console.WriteLine("Person: " + obj._1 + " - " + obj._2 + " - " + obj._3 + " - " + obj._4);
//insert SQL goes here
}
Any ideas??

Instead of calling Value on the element, consider using a string cast. LINQ to XML safely returns null if the element doesn't exist. Try the following:
var data = XElement.Load(#"http://www.un.org/sc/committees/1267/AQList.xml");
var individuals = data.Descendants("INDIVIDUAL")
.Select(i => new {
First = (string)i.Element("FIRST_NAME"),
Middle = (string)i.Element("SECOND_NAME"),
Last = (string)i.Element("THIRD_NAME")
});
If you want to be more flexible and get all of the name fields, you can do something like the following. (I'll leave the process of grouping individuals as an additional homework assignment ;-)
data.Descendants("INDIVIDUAL").Elements()
.Where (i =>i.Name.LocalName.EndsWith("_NAME" ))
.Select(i => new { FieldName= i.Name.LocalName, Value=i.Value});

Why don't you use XmlSerializer and LINQ instead ?
As explained in this answer, generate your classes by pasting in a new CS file :
menu EDIT > Paste Special > Paste XML As Classes.
Then grab your data as easily as follows :
var serializer = new XmlSerializer(typeof (CONSOLIDATED_LIST));
using (FileStream fileStream = File.OpenRead(#"..\..\aqlist.xml"))
{
var list = serializer.Deserialize(fileStream) as CONSOLIDATED_LIST;
if (list != null)
{
var enumerable = list.INDIVIDUALS.Select(s => new
{
FirstName = s.FIRST_NAME,
SecondName = s.SECOND_NAME,
ThirdName = s.THIRD_NAME,
FourthName = s.FOURTH_NAME
});
}
}
You can then specify any predicate that better suits your needs.
Going this path will be a huge time-saver and less error-prone, no need to use strings to access fields, strong typing etc ...

Check if XML node value already exists in xml file using c#

Please note that I'm new to C# and I learn it right now :) I couldn't find something similar to my problem, so I came here.
I have an application in which I add customers (it's in the final stage). All customers are stored in an XML file. Every single customer gets a new customer number. In my xml file I got an XmlNode called CustNo. Now if the user add a new customer and type in a number which already exist, it should pop up a message box to say that this number already exists. I got this c# code:
XDocument xdoc = XDocument.Load(path + "\\save.xml");
var xmlNodeExist = String.Format("Buchhaltung/Customers/CustNo");
var CustNoExist = xdoc.XPathSelectElement(xmlNodeExist);
if (CustNoExist != null)
{
MessageBox.Show("asdf");
}
And my XML file looks like this:
<Buchhaltung>
<Customers>
<CustNo>12</CustNo>
<Surname>Random</Surname>
<Forename>Name</Forename>
<Addr>Address</Addr>
<Zip>12345</Zip>
<Place>New York</Place>
<Phone>1234567890</Phone>
<Mail>example#test.com</Mail>
</Customers>
<Customers>
<CustNo>13</CustNo>
<Surname>Other</Surname>
<Forename>Forename</Forename>
<Addr>My Address</Addr>
<Zip>67890</Zip>
<Place>Manhattan</Place>
<Phone>0987654321</Phone>
<Mail>test#example.com</Mail>
</Customers>
</Buchhaltung>
But then the message box always pops up. What am I doing wrong?

That's because your XPath return all CustNo elements, no matter of it's content.
Try following:
var myNumber = 12;
var xmlNodeExist = String.Format("Buchhaltung/Customers/CustNo[. = {0}]", myNumber.ToString());
or using First and LINQ to XML:
var myNumber = 12;
var xmlNodeExist = "Buchhaltung/Customers/CustNo";
var CustNoExist = xdoc.XPathSelectElements(xmlNodeExist).FirstOrDefault(x => (int)x == myNumber);

You are currently testing for existance of any 'CustNo' element. See this reference about the XPath syntax.
Your XPath should say something like this:
Buchhaltung//Customers[CustNo='12']
which would say "any customers element containing a 'CustNo' element with value = '12'"
Combining that with your current code:
var custNoGivenByCustomer = "12";
var xmlNodeExistsXpath = String.Format("Buchhaltung//Customers[CustNo='{0}']", custNoGivenByCustomer );
var CustNoExist = xdoc.XPathSelectElement(xmlNodeExistsXpath);

You can use LINQ to XML
var number = textBox1.Text;
var CustNoExist = xdoc.Descendants("CustNo").Any(x => (string)x == number);
if(CustNoExist)
{
MessageBox.Show("asdf");
}

This is because you select the CustNo elements regardless of their value. This will filter it to the desired customer number:
int custNo = 12;
var xmlNodeExist = String.Format("Buchhaltung/Customers[CustNo={0}]", custNo);
It selects the Customers elements instead, but since you're just checking for existence, that's unimportant.
W3Schools has a good tutorial/reference on XPath.

Parsing XML: NullReferenceException for Variable Elements

I'm getting a text string from a website and parsing it into an XDocument. I'm looking to feed the value of certain elements into a very simple object (named NWSevent). My problem is that the original string changes and the XML tree varies; sometimes there are numerous events, up to 40, sometimes there is only one, and sometimes there is only one that does not have all the characteristics. If there are no alerts, then the "event" element has a title, but no areaDesc, summary, or severity.
I have two constructors for NWSevent, one takes in a single string, the other takes in four string arguments. I'm having trouble getting around a NullReferenceException. The if statement below can't do it because there is no value to compare. I'd appreciate any help.
public static void ParseWeatherData(String xmlString)
{
String ticker = string.Empty;
XDocument root = XDocument.Parse(xmlString);
XNamespace ns = XNamespace.Get("http://www.w3.org/2005/Atom");
XNamespace nsCap = XNamespace.Get("urn:oasis:names:tc:emergency:cap:1.1");
//get list of entry elements, set conditions for title, areaDesc, etc
var xlist = root.Descendants(ns + "entry").Select(elem => new
{ //use first or default to deal with possiblity of null return
Title = elem.Descendants(ns + "title").FirstOrDefault(),
AreaDesc = elem.Descendants(nsCap + "areaDesc").FirstOrDefault(),
Severity = elem.Descendants(nsCap + "severity").FirstOrDefault(),
Summary = elem.Descendants(ns + "summary").FirstOrDefault()
});
foreach (var el in xlist) //need to address null values when no alerts
{
if (el.AreaDesc.Value != null) //causes yellow null ERROR; no value exists for el.areaDesc.value
{
String titleIn = el.Title.Value;
String areaIn = el.AreaDesc.Value;
String severityIn = el.Severity.Value;
String summaryIn = el.Summary.Value;
new Models.NWSevent(titleIn, areaIn, severityIn, summaryIn);
}
else
{
String titleIn = el.Title.Value;
new Models.NWSevent(titleIn);
}
}

Embarassing! Props to Dweeberly for pointing it out. I just need to change the if statement from
if (el.AreaDesc.Value != null){}
to if (el.AreaDesc != null){}

get xelement attribute value

I have an XElement that looks like this:
<User ID="11" Name="Juan Diaz" LoginName="DN1\jdiaz" xmlns="http://schemas.microsoft.com/sharepoint/soap/directory/" />
How can I use XML to extract the value of the LoginName attribute? I tried the following, but the q2 "Enumeration yielded no results".
var q2 = from node in el.Descendants("User")
let loginName = node.Attribute(ns + "LoginName")
select new { LoginName = (loginName != null) };
foreach (var node in q2)
{
Console.WriteLine("LoginName={0}", node.LoginName);
}

var xml = #"<User ID=""11""
Name=""Juan Diaz""
LoginName=""DN1\jdiaz""
xmlns=""http://schemas.microsoft.com/sharepoint/soap/directory/"" />";
var user = XElement.Parse(xml);
var login = user.Attribute("LoginName").Value; // "DN1\jdiaz"

XmlDocument doc = new XmlDocument();
doc.Load("myFile.xml"); //load your xml file
XmlNode user = doc.getElementByTagName("User"); //find node by tag name
string login = user.Attributes["LoginName"] != null ? user.Attributes["LoginName"].Value : "unknown login";
The last line of code, where it's setting the string login, the format looks like this...
var variable = condition ? A : B;
It's basically saying that if condition is true, variable equals A, otherwise variable equals B.

from the docs for XAttribute.Value:
If you are getting the value and the attribute might not exist, it is more convenient to use the explicit conversion operators, and assign the attribute to a nullable type such as string or Nullable<T> of Int32. If the attribute does not exist, then the nullable type is set to null.

I ended up using string manipulation to get the value, so I'll post that code, but I would still like to see an XML approach if there is one.
string strEl = el.ToString();
string[] words = strEl.Split(' ');
foreach (string word in words)
{
if (word.StartsWith("LoginName"))
{
strEl = word;
int first = strEl.IndexOf("\"");
int last = strEl.LastIndexOf("\"");
string str2 = strEl.Substring(first + 1, last - first - 1);
//str2 = "dn1\jdiaz"
}
}

Check if an element exists when parsing XML

I'm parsing XML. I normally parse it the way I show in the code below which is straightforward The problem is that I don't own the XML I'm parsing and I can't change it. Sometimes there is no thumbnail element (there are no tags) and I get an Exception.
Is there a way to maintain this simplicity and check if the element exists? Or do I have to get first an XElement list with LINQ, to then check it and fill only the existing object properties?
void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
XDocument dataDoc = XDocument.Load(new StringReader(e.Result));
var listitems = from noticia in dataDoc.Descendants("Noticia")
select new News()
{
id = noticia.Element("IdNoticia").Value,
published = noticia.Element("Data").Value,
title = noticia.Element("Titol").Value,
subtitle = noticia.Element("Subtitol").Value,
thumbnail = noticia.Element("Thumbnail").Value
};
itemList.ItemsSource = listitems;
}

[Edit]Jon Skeet's answer should be the accepted answer. It is far more readable and easier to apply.[/edit]
Create an extension method like this :
public static string TryGetElementValue(this XElement parentEl, string elementName, string defaultValue = null)
{
var foundEl = parentEl.Element(elementName);
if (foundEl != null)
{
return foundEl.Value;
}
return defaultValue;
}
then, change your code like this :
select new News()
{
id = noticia.TryGetElementValue("IdNoticia"),
published = noticia.TryGetElementValue("Data"),
title = noticia.TryGetElementValue("Titol"),
subtitle = noticia.TryGetElementValue("Subtitol"),
thumbnail = noticia.TryGetElementValue("Thumbnail", "http://server/images/empty.png")
};
This approach allows you to keep a clean code with isolating the check of element presence. It also allow you to define a default value, which can be helpful

Instead of using the Value property, if you cast to string you'll just get a null reference instead:
void wc_DownloadStringCompleted(object sender,
DownloadStringCompletedEventArgs e)
{
XDocument dataDoc = XDocument.Load(new StringReader(e.Result));
var listitems = from noticia in dataDoc.Descendants("Noticia")
select new News()
{
id = (string) noticia.Element("IdNoticia"),
published = (string) noticia.Element("Data"),
title = (string) noticia.Element("Titol"),
subtitle = (string) noticia.Element("Subtitol"),
thumbnail = (string) noticia.Element("Thumbnail")
};
itemList.ItemsSource = listitems;
}
That uses the explicit conversion from XElement to string, which handles a null input by returning a null output. The same is true for all explicit conversions on XAttribute and XElement to nullable types, including nullable value types such as int? - you just need to be careful if you're using nested elements. For example:
string text = (string) foo.Element("outer").Element("inner");
will give a null reference if inner is missing, but will still throw an exception if outer is missing.
If you want a "default" value, you can use the null coalescing operator (??):
string text = (string) foo.Element("Text") ?? "Default value";

You could just use the System.Xml.Serialization.XmlSerializer to deserialize it from xml to an object. Then if the element doesn't exist the property of the object will just get it's default value.
Have a look here: http://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlserializer.aspx
or the new path
https://learn.microsoft.com/en-us/dotnet/api/system.xml.serialization.xmlserializer

You may use the code below:
string content = item.Element("Content") == null ? "" : item.Element("Content").Value;