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Is my usage of LINQ to XML correct when I'm trying to find multiple values in the same XML file?

I have to extract values belonging to certain elements in an XML file and this is what I ended up with.
XDocument doc = XDocument.Load("request.xml");
var year = (string)doc.Descendants("year").FirstOrDefault();
var id = (string)doc.Descendants("id").FirstOrDefault();
I'm guessing that for each statement I'm iterating through the entire file looking for the first occurrence of the element called year/id. Is this the correct way to do this? It seems like there has to be a way where one would avoid unnecessary iterations. I know what I'm looking for and I know that the elements are going to be there even if the values may be null.
I'm thinking in the lines of a select statement with both "year" and "id" as conditions.
For clearance, I'm looking for certain elements and their respective values. There'll most likely be multiple occurrences of the same element but FirstOrDefault() is fine for that.
Further clarification:
As requested by the legend Jon Skeet, I'll try to clarify further. The XML document contains fields such as <year>2015</year> and <id>123032</id> and I need the values. I know which elements I'm looking for, and that they're going to be there. In the sample XML below, I would like to get 2015, The Emperor, something and 30.
Sample XML:
<?xml version="1.0" encoding="UTF-8"?>
<documents xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<make>Apple</make>
<year>2015</year>
<customer>
<name>The Emperor</name>
<level2>
<information>something</information>
</level2>
<age>30</age>
</customer>

A code that doesn't parse the whole xml twice would be like:
XDocument doc = XDocument.Load("request.xml");
string year = null;
string id = null;
bool yearFound = false, idFound = false;
foreach (XElement ele in doc.Descendants())
{
if (!yearFound && ele.Name == "year")
{
year = (string)ele;
yearFound = true;
}
else if (!idFound && ele.Name == "id")
{
id = (string)ele;
idFound = true;
}
if (yearFound && idFound)
{
break;
}
}
As you can see you are trading lines of code for speed :-) I do feel the code is still quite readable.
if you really need to optimize up to the last line of code, you could put the names of the elements in two variables (because otherwise there will be many temporary XName creation)
// before the foreach
XName yearName = "year";
XName idName = "id";
and then
if (!yearFound && ele.Name == yearName)
...
if (!idFound && ele.Name == idName)

Simple XML parsing with LINQ

I would like to parse this XML :
<?xml version="1.0" encoding="Windows-1252" ?>
<TEST>Login inexistant</TEST>
I wrote this code
var result = from item in XElement.Parse(m_strRetour).Descendants("TEST")
select item;
return result.First().ToString();
m_strRetour is a string that contains my XML.
After execution, result is empty.
What am I doing wrong?

TEST seems to be your root node, so it can't be a Descendant.
To get the value out of it you could try this.
var xml = "<?xml version='1.0' encoding='Windows-1252' ?><TEST>Login inexistant</TEST>";
var result = XElement.Parse(xml);
var value = result.Value;

XElement.Parse will return the TEST element itself - which doesn't have any descendants. (Also, there's no benefit in using a query expression here. Whenever you write from x in y select x you should consider whether you couldn't just use y instead...)
You could parse it as an XDocument instead, in which case there would be a TEST descendant... or you could just use the XElement itself.
What are you really trying to achieve though? Does your real XML only have a single element?

Xml updating with linq not working when quering

I have problem i'm trying to update a specific part of the XML with the linq query but it doesn't work. So i an xml file:
<?xml version="1.0" encoding="utf-8"?>
<DesignConfiguration>
<Design name="CSF_Packages">
<SourceFolder>C:\CSF_Packages</SourceFolder>
<DestinationFolder>C:\Documents and Settings\xxx</DestinationFolder>
<CopyLookups>True</CopyLookups>
<CopyImages>False</CopyImages>
<ImageSourceFolder>None</ImageSourceFolder>
<ImageDesinationFolder>None</ImageDesinationFolder>
</Design>
</DesignConfiguration>
I want to select the part where the part where there is Design name="somethning" and get the descendants and then update the descendants value that means this part:
<SourceFolder>C:\CSF_Packages</SourceFolder>
<DestinationFolder>C:\Documents and Settings\xxx</DestinationFolder>
<CopyLookups>True</CopyLookups>
<CopyImages>False</CopyImages>
<ImageSourceFolder>None</ImageSourceFolder>
<ImageDesinationFolder>None</ImageDesinationFolder>
I have this code:
XDocument configXml = XDocument.Load(configXMLFileName);
var updateData = configXml.Descendants("DesignConfiguration").Elements().Where(el => el.Name == "Design" &&
el.Attribute("name").Value.Equals("CSF_Packages")).FirstOrDefault();
configXml.Save(configXMLFileName);
I'm getting the null data in the updateData varibale. When I'm trying the Descendat's function through QuickWatch it also returns a null value. When I'm checking the configXML variable it has data that is my whole xml. What am I doing wrong?

Try this:
var updateData =
confixXml
.Root //Root Element
.Elements("Design") //All elements under root called Design
.Where(element => (String)element.Attribute("name") == "AFP_GRAFIKA") //Find the one with the name Attribute of AFP_GRAFIKA
.FirstOrDefault(); //Grab the first one it finds or return null.
if (updateData != null)
{
var myElements =
updateData
.Elements(); //All the elements under the Design node
}

XDocument xml = XDocument.Load("");
XElement settings = (from children in xml.Descendants("DesignConfiguration")
where children.Name.Equals("Design") && children.Attribute("name").Equals("CSF_Packages")
select children).FirstOrDefault();
settings.Element("SourceFolder").SetValue("filepath");
settings.Element("CopyImages").SetValue(true);

Ok, so I've managed to fix the problem. I don't know why but it worked. It seems that the Descendants function returns null as a stand alone function but with linq it works. So for my solution only thing what should be done is this:
var updateData = (from s in configXml.Descendants("Design")
where s.Attribute("name").Value == design.DesignName
select s).First();
At first before I sent you my question I've tried this but I didn't have the select s part. Besides when I wrote the where s.Atribute part in the curly brackets I've inserted the design.DesignName object instead of the name of the attribute. So no it works ok. Thanks for your help and everything. Til nex time. Have a nice day/night everyone :)

Because DesignConfiguration was your root node, the Descendants("DesignConfiguration) was returning null. By using the .Descendants("Design"), you were looking at child nodes, not the self.

I want to return the only/single string value from an XML Element using Linq

I want to return the latitude node (for example) from the following XML string (from Yahoo geocoding API.)
<ResultSet version="1.0">
<Error>0</Error>
<ErrorMessage>No error</ErrorMessage>
<Locale>us_US</Locale>
<Quality>60</Quality>
<Found>1</Found>
<Result>
<quality>87</quality>
<latitude>37.68746446</latitude>
<longitude>-79.6469878</longitude>
<offsetlat>30.895931</offsetlat>
<offsetlon>-80.281192</offsetlon>
<radius>500</radius>
<name></name>
<line1>123 Main Street</line1>
<line2>Greenville, SC 29687</line2>
<line3></line3>
<line4>United States</line4>
<house>123</house>
<street>Main Street</street>
<xstreet></xstreet>
<unittype></unittype>
<unit></unit>
<postal>29687</postal>
<neighborhood></neighborhood>
<city>Greenville</city>
<county>Greenville County</county>
<state>South Carolina</state>
<country>United States</country>
<countrycode>US</countrycode>
<statecode>SC</statecode>
<countycode></countycode>
<uzip>29687</uzip>
<hash>asdfsdfas</hash>
<woeid>127757446454</woeid>
<woetype>11</woetype>
</Result>
</ResultSet>
I already have this XML successfully loaded into an XElement instance but I cannot seem to be able to find the way to load the latitude node (for example) into a string variable. If there is no node or the node is empty then I would like to get a Null or Nullstring. If there is more than one (there won't be but just in case) then return the first instance.
I thought this would be easy but I can't get it to work. All of the Linq queries I have tried are returning null.
While I am at it if you could explain it with enough detail so that I can also get the Error node. I only mention it because it is at a different level.
Thanks.
Seth

To get latitude's value:
var latitudeElement = resultXML.Descendants("latitude").FirstOrDefault();
string latitude = latitudeElement == null ? String.Empty : latitudeElement.Value;
And you could get the Error element with the following:
var errorElement = resultXML.Descendants("Error").First();
I'm using resultXML as the reference to the parsed XML.

Make sure you're using the System.Xml.XPath namespace, and try:
var doc = XDocument.Parse(<your xml here>);
var el = doc.XPathSelectElement("ResultSet/Result/latitude");
el should contain an XElement class or null if the node wasn't found.
See the MSDN docs for XPath 1.0 for more info on how to use it.

How to save XML node back into XML file with LINQ-to-XML?

I've got an XML file which I use to create objects, change the objects, then save the objects back into the XML file.
What do I have to change in the following code so that it extracts a node from the XML based on the id, replaces that node with the new one, and saves it back into the XML?
The following gives me 'System.Xml.Linq.XElement' does not contain a constructor that takes '0' arguments':
//GET ALL SMARTFORMS AS XML
XDocument xmlDoc = null;
try
{
xmlDoc = XDocument.Load(FullXmlDataStorePathAndFileName);
}
catch (Exception ex)
{
HandleXmlFileNotFound(ex);
}
//EXTRACT THE NODE THAT NEEDS TO BE REPLACED
XElement oldElementToOverwrite = xmlDoc.Descendants("smartForm")
.Where(sf => (int)sf.Element("id") == 2)
.Select(sf => new XElement());
//CREATE THE NODE THAT WILL REPLACE IT
XElement newElementToSave = new XElement("smartForm",
new XElement("id", this.Id),
new XElement("idCode", this.IdCode),
new XElement("title", this.Title)
);
//OVERWRITE OLD WITH NEW
oldElementToOverwrite.ReplaceWith(newElementToSave);
//SAVE XML BACK TO FILE
xmlDoc.Save(FullXmlDataStorePathAndFileName);
XML file:
<?xml version="1.0" encoding="utf-8" ?>
<root>
<smartForm>
<id>1</id>
<whenCreated>2008-12-31</whenCreated>
<itemOwner>system</itemOwner>
<publishStatus>published</publishStatus>
<correctionOfId>0</correctionOfId>
<idCode>customerSpecial</idCode>
<title>Edit Customer Special</title>
<description>This form has a special setup.</description>
<labelWidth>200</labelWidth>
</smartForm>
<smartForm>
<id>2</id>
<whenCreated>2008-12-31</whenCreated>
<itemOwner>system</itemOwner>
<publishStatus>published</publishStatus>
<correctionOfId>0</correctionOfId>
<idCode>customersMain</idCode>
<title>Edit Customer</title>
<description>This form allows you to edit a customer.</description>
<labelWidth>100</labelWidth>
</smartForm>
<smartForm>
<id>3</id>
<whenCreated>2008-12-31</whenCreated>
<itemOwner>system</itemOwner>
<publishStatus>published</publishStatus>
<correctionOfId>0</correctionOfId>
<idCode>customersNameOnly</idCode>
<title>Edit Customer Name</title>
<description>This form allows you to edit a customer's name only.</description>
<labelWidth>100</labelWidth>
</smartForm>
</root>

Well, the error has nothing to do with saving, or even with replacement - it has to do with you trying to create an XElement without specifying the name. Why are you trying to use Select at all? My guess is you just want to use Single:
XElement oldElementToOverwrite = xmlDoc.Descendants("smartForm")
.Where(sf => (int)sf.Element("id") == 2)
.Single();
(As Noldorin notes, you can give Single a predicate to avoid using Where at all. Personally I quite like to split the two operations up, but they'll be semantically equivalent.)
That will return the single element in the sequence, or throw an exception if there are 0 elements or more than one. Alternatives are to use SingleOrDefault, First, or FirstOrDefault:
SingleOrDefault if it's legal to have 0 or 1
First if it's legal to have 1 or more
FirstOrDefault if it's legal to have 0 or more
If you're using an "OrDefault" one, the result will be null if there are no matches.

I think the problem is simply your use of the Select call in the statement assigning oldElementToOverwrite. You actually seem to want the Single extension method.
XElement oldElementToOverwrite = xmlDoc.Descendants("smartForm")
.Single(sf => (int)sf.Element("id") == 2)