Develop Reference

how to get value from xml by Linq

i was reading huge xml file of 5GB size by using the following code, and i was success to get the first element Testid but failed to get another element TestMin coming under different namespace
this is the xml i am having
which i am getting as null
.What is wrong here?
EDIT
GMileys answer giving error like The ':' character, hexadecimal value 0x3A, cannot be included in a name

The element es:qRxLevMin is a child element of xn:attributes, but it looks like you are trying to select it as a child of xn:vsDataContainer, it is a grandchild of that element. You could try changing the following:
var dataqrxlevmin = from atts in pin.ElementsAfterSelf(xn + "VsDataContainer")
select new
{
qrxlevmin = (string)atts.Element(es + "qRxLevMin"),
};
To this:
var dataqrxlevmin = from atts in pin.Elements(string.Format("{0}VsDataContainer/{1}attributes", xn, es))
select new
{
qrxlevmin = (string)atts.Element(es + "qRxLevMin"),
};
Note: I changed your string concatenation to use string.Format for readability purposes, either is technically fine to use, but string.Format is a better approach.

What about this approach?
XDocument doc = XDocument.Load(path);
XName utranCellName = XName.Get("UtranCell", "un");
XName qRxLevMinName = XName.Get("qRxLevMin", "es");
var cells = doc.Descendants(utranCellName);
foreach (var cell in cells)
{
string qRxLevMin = cell.Descendants(qRxLevMinName).FirstOrDefault();
// Do something with the value
}

try this code which is very similar to your code but simpler.
using (XmlReader xr = XmlReader.Create(path))
{
xr.MoveToContent();
XNamespace un = xr.LookupNamespace("un");
XNamespace xn = xr.LookupNamespace("xn");
XNamespace es = xr.LookupNamespace("es");
while (!xr.EOF)
{
if(xr.LocalName != "UtranCell")
{
xr.ReadToFollowing("UtranCell", un.NamespaceName);
}
if(!xr.EOF)
{
XElement utranCell = (XElement)XElement.ReadFrom(xr);
}
}
}

actually namespace was the culprit,what i did is first loaded the small section i am getting from.Readform method in to xdocument,then i removed all the namespace,then i took the value .simple :)

How properly work with LINQ to XML?

I have generated such xml file
<?xml version="1.0" encoding="utf-8"?>
<Requestes>
<Single_Request num="1">
<numRequest>212</numRequest>
<IDWork>12</IDWork>
<NumObject>21</NumObject>
<lvlPriority>2</lvlPriority>
<NumIn1Period>21</NumIn1Period>
</Single_Request>
</Requestes>
My aim is to get IDWork,numRequest and etc elements. I tried to get them this way:
foreach (XElement el in doc.Root.Elements())
{
if (el.Name == "Single_Request")
{
string num = el.Elements("numRequest").Value;
// but he says, that he cant do this .Value because it doest exist at all
}
}
How to fix this?

You have this error, because Elements("numRequest") returns collection of elements, not single element. You should use Element("numRequest") instead.
Also I suggest you to use query for getting elements by name instead of enumerating all elements and verifying their names:
var request = doc.Root.Element("Single_Request");
var num = (int)request.Element("numRequest");
Usually you use anonymous types or custom objects to group values parsed from xml:
var query = from r in doc.Root.Elements("Single_Request")
where (int)r.Attribute("num") == 1 // condition
select new {
NumRequest = (int)request.Element("numRequest"),
IdWork = (int)request.Element("IDWork"),
NumObject = (int)request.Element("NumObject")
};
var request = query.SinlgleOrDefault();
// use request.IdWork

Querying xml into structure

I believe I am getting XDocument and XElement aspects confused. I am trying to:
Load an xml file
Query an attribute of an element's name
Write aspects of the found element to a structure.
Simple Structure, called Rule:
public struct Rule
{
public String keyDB;
public String eventLog;
}
XML Structure:
<?xml version="1.0" encoding="utf-8" ?>
<Error_List>
<Error code="0xC004C003">
<KeyDB>
default key
</KeyDB>
<EventLog>
default event
</EventLog>
</Error>
<Error code="000000000">
<KeyDB>
non-default key
</KeyDB>
<EventLog>
non-default event
</EventLog>
</Error>
</Error_List>
Set Rule rule = new Rule();
If I pass into my method "000000000" I am looking to set rule.keyDB = "non-default key" and rule.eventLog = "non-default event". I'm pretty sure that this is possible, but that I just have my variables mixed up.
Edit:
My code, thus far, has been unsuccessful and incomplete. I have
IEnumerable<XElement> query = (from elem in rulesXml.Root.Elements("Error")
where (String)elem.Attribute("code") == this.errorCode.ToString()
select elem);
but am unsure where to go from there.

Linq-to-XML is extremely powerful and quite straightforward to understand once you master Linq. You can find a lot of tutorials about these two topics.
Here is what you can do:
string myCode = "000000000"; // Error Code to find
XDocument xDocument = XDocument.Load("C:/Path to the file.xml"); // Loads the Xml file to a XDocument
Rule rule = (from errorNode in xDocument.Descendants("Error") // Go through Error elements
where errorNode.Attribute("code").Value == myCode // That has the specified code attribute
select new Rule
{
keyDB = errorNode.Element("KeyDB").Value, // Gets the KeyDB element value of the Error node
eventLog = errorNode.Element("EventLog").Value // Gets the EventLog element value of the Error node
}).FirstOrDefault();
Update
If an Error element can have no code attribute or no KeyDB or EventLog attribute. Use the explicit type casting to retrieve their value. ie. Instead of writing Element.Attribute("...").Value write (string)Element.Attribute("...") (same for Element("..."))
Rule rule = (from errorNode in xDocument.Descendants("Error") // Go through Error elements
where (string)errorNode.Attribute("code") == myCode // That has the specified code attribute
select new Rule
{
keyDB = (string)errorNode.Element("KeyDB"), // Gets the KeyDB element value of the Error node
eventLog = (string)errorNode.Element("EventLog") // Gets the EventLog element value of the Error node
}).FirstOrDefault();

Try using the ILookup:
Error code is set as the key for the lookup.
public struct Rule
{
public String keyDB;
public String eventLog;
}
class Program
{
static void Main(string[] args)
{
XDocument xdoc = XDocument.Load("src.xml");
ILookup<string, Rule> lookup = xdoc.Descendants("Error").ToLookup(x => x.Attribute("code").Value, x => new Rule() { keyDB = x.Element("KeyDB").Value, eventLog = x.Element("EventLog").Value });
//Perform operation based on the error code from the lookup
Console.Read();
}
}

How to get XElement's value and not value of all child-nodes?

Sample xml:
<parent>
<child>test1</child>
<child>test2</child>
</parent>
If I look for parent.Value where parent is XElement, I get "test1test2".
What I am expecting is "". (since there is no text/value for .
What property of XElement should I be looking for?

When looking for text data in the <parent> element you should look for child nodes that have NodeType properties equal to XmlNodeType.Text. These nodes will be of type XText. The following sample illustrates this:
var p = XElement
.Parse("<parent>Hello<child>test1</child>World<child>test2</child>!</parent>");
var textNodes = from c in p.Nodes()
where c.NodeType == XmlNodeType.Text
select (XText)c;
foreach (var t in textNodes)
{
Console.WriteLine(t.Value);
}
Update: if all you want is the first Text node, if any, here's an example using LINQ method calls instead of query comprehension syntax:
var firstTextNode = p.Nodes().OfType<XText>().FirstOrDefault();
if (firstTextNode != null)
{
var textValue = firstTextNode.Value;
...do something interesting with the value
}
Note: using First() or FirstOrDefault() will be more performant than Count() > 0 in this scenario. Count always enumerates the whole collection while FirstOrDefault() will only enumerate until a match is found.

It is amazing that a coder somewhere at Microsoft thought that returning all text values as a concatenated and undelimited string would be useful. Luckily, another MS developer wrote an XElement extension to return what they call the "Shallow Value" of the text node here. For those who get the willies from clicking on links, the function is below...
public static string ShallowValue(this XElement element)
{
return element
.Nodes()
.OfType<XText>()
.Aggregate(new StringBuilder(),
(s, c) => s.Append(c),
s => s.ToString());
}
And you call it like this, because it gives you all the whitespace too (or, come to think of it, you could trim it in the extension, whatever)
// element is a var in your code of type XElement ...
string myTextContent = element.ShallowValue().Trim();

You could concatenate the value of all XText nodes in parent:
XElement parent = XElement.Parse(
#"<parent>Hello<child>test1</child>World<child>test2</child>!</parent>");
string result = string.Concat(
parent.Nodes().OfType<XText>().Select(t => t.Value));
// result == "HelloWorld!"
For comparison:
// parent.Value == "Hellotest1Worldtest2!"
// (parent.HasElements ? "" : parent.Value) == ""

msdn says:
A String that contains all of the text content of this element. If there are multiple text nodes, they will be concatenated.
So the behaviour is to be expected.
You could solve your problem by doing:
string textContent = parent.HasElements ? "" : parent.Value;

// Create the XElement
XElement parent = XElement.Parse(
#"<parent>Hello<child>test1</child>World<child>test2</child>!</parent>");
// Make a copy
XElement temp=new XElement(parent);
// remove all elements but root
temp.RemoveNodes();
// now, do something with temp.value, e.g.
Console.WriteLine(temp.value);

Change Value of the last Attribute in an XML c#

I was working on a bunch of XMLs that all share an attribute that contains the string "name" in them. The following code selects the attribute with string "name" in it and assign a new value to it.
public void updateXmlFile(string strFileName)
{
try
{
//Load the Document
XmlDocument doc = new XmlDocument();
doc.Load(strFileName);
//Set the changed Value
string newValue = GetUniqueKey();
//Select all nodes in the XML then choose from them
//the first node that contain string "name" in it
XmlNodeList list = doc.SelectNodes("//#*");
XmlNode filteredNode = list.Cast<XmlNode>()
.First(item => item.Name.ToLower().Contains("name"));
//Assign the newValue to the value of the node
filteredNode.Value = newValue;
doc.Save(strFileName);
}
catch (XmlException xex) { Console.WriteLine(xex); }
}
Now a new XMLs were added that dosen't have the string "name" in them, so instead of modifying the attribute with string "name" in it I decided to simply modify the last attribute no matter what it was (not the first)
Can anybody tell me how to do that?
EDIT
Here is an example of my XML
<?xml version="1.0" encoding="utf-8"?>
<CO_CallSignLists Version="24" ModDttm="2010-09-13T06:45:38.873" ModUser="EUADEV\SARE100" ModuleOwner="EUADEVS06\SS2008" CreateDttm="2009-11-05T10:19:31.583" CreateUser="EUADEV\A003893">
<CoCallSignLists DataclassId="E3FC5E2D-FE84-492D-AD94-3ACCED870714" EntityId="E3FC5E2D-FE84-492D-AD94-3ACCED870714" MissionID="4CF71AB2-0D92-DE11-B5D1-000C46F3773D" BroadcastType="S" DeputyInSpecialList="1" SunSpots="1537634cb70c6d80">
<CoCallSigns EntityId="DEBF1DDB-3C92-DE11-A280-000C46F377C4" CmdID="C45F3EF1-1292-DE11-B5D1-000C46F3773D" ModuleID="6CB497F3-AD63-43F1-ACAE-2C5C3B1D7F61" ListType="HS" Name="Reda Sabassi" Broadcast="INTO" PhysicalAddress="37" IsGS="1" HCId="0" CommonGeoPos="1" GeoLat="0.0000000" GeoLong="0.0000000">
<CoRadios EntityId="E1BF1DDB-3C92-DE11-A280-000C46F377C4" RadioType="HF" />
</CoCallSigns>
</CoCallSignLists>
</CO_CallSignLists>
#Alex: You notice that the "SunSpots" attribute (last attribute in the first child element) is successfully changed. But now when I wanna load the XML back into the DB it gives me an error
Here is the modified code
public void updateXmlFile(string strFileName)
{
try
{
XDocument doc = XDocument.Load(strFileName);
XAttribute l_attr_1 = (doc.Elements().First().Elements().First().Attributes().Last());
l_attr_1.Value = GetUniqueKey();
Console.WriteLine("Name: {0} Value:{1}", l_attr_1.Name, l_attr_1.Value);
doc.Save(strFileName);
}
catch (XmlException xex) { Console.WriteLine(xex); }
}
I was thinking of making an if statment which checks if the XML has an attribute that contains string "name" in it (since most of my XMLs has an attribute that contains name in them) if it does then change the attribute's value if not look for the last attribute and change it.. not the best solution but just throwing it out there

Then definitely use Linq to XML.
Example:
using System.Xml.Linq;
string xml = #"<?xml version=""1.0"" encoding=""utf-8""?>
<Commands Version=""439"" CreateUser=""Reda"">
<CmCommands DataclassId=""57067ca8-ef96-4d2e-a085-6bd7e8b24126"" OrderName = ""Tea"" Remark=""Black"">
<CmExecutions EntityId=""A9A5B0F2-6AB4-4619-9106-B0F85F86EE01"" Lock=""n"" />
</CmCommands>
</Commands>";
XDocument x = XDocument.Parse(xml);
Debug.Print(x.Elements().First().Elements().First().Attributes().Last().Value);
// Commands ^ CmCommands ^ Remark ^
That is, word for word, the last attribute of the first child of the first element.
You can also query for element/attribute names, like:
Debug.Print(x.Descendants(XName.Get("CmCommands", "")).First().Attribute(XName.Get("Remark", "")).Value);
And of course you can use all of the Linq goodness like Where, Select, Any, All etc.
Note: replace XDocument.Parse with XDocument.Load if appropriate etc.

I've not tested this but you should be able to do all of this in the XPath expression. Something like this:
//#*[contains(node-name(.), 'name')][last()]
This will return only the last attribute with the string name anywhere in its name.
If you only want the last attribute, irrespective of it's name, use this:
//#*[last()]

Look at class XmlAttributeCollection. You can get this collection by reading property Attributes of XmlNode. Just get the last by index.

Instead of .First(), use an extension method like this:
public static T LastOrDefault<T>(this IEnumerable<T> list)
{
T val = null;
foreach(T item in list)
{
val = item;
}
return val;
}