Develop Reference

Using LINQ to exclude a Child Node from a collection of the same name

Per this XML, please note that BBB exists on two node levels.
<?xml version="1.0" encoding="utf-8"?>
<AAA>
<BBB>
<BBB>ONE</BBB>
<CCC>1</CCC>
<DDD>2</DDD>
<EEE>3</EEE>
</BBB>
<BBB>
<BBB>TWO</BBB>
<CCC>4</CCC>
<DDD>5</DDD>
<EEE>6</EEE>
</BBB>
<BBB>
<BBB>THREE</BBB>
<CCC>7</CCC>
<DDD>8</DDD>
<EEE>9</EEE>
</BBB>
</AAA>
I want to derive a collection of top level BBB's and extract them to their own file, with a file name based on the inner BBB.
My code is this:
XDocument xdoc = XDocument.Load(sourceFile);
var lv1s = from lv1 in xdoc.Descendants("AAA") select lv1;
var lv2s = from lv2 in xdoc.Descendants("BBB") select lv2;
foreach (var lv2 in lv2s)
{
var name = lv2.Element("BBB").Value;
lv2.Save(#"c:\temp\" + name + ".xml");
}
Problem is, LVL2 is picking up both the parent and descendants BBB.
Can't seem to find a method that effectively filters out descendants.
For example I thought this was the key, but it yielded no results:
var lv2s = from lv2 in xdoc.Elements("BBB") select lv2;
Hoping you can provide me a ways to deal with the problem.
-------------------- EDIT --------------------
Okay I see what I did wrong. A typo.
LVL2 should have leveraged LVL1, like this:
var lv2s = from lv2 in lv1s.Elements("BBB") select lv2;
That said, octavioccl's approach was much better than the bloated solution I came up with:
var parentBbbs =xdoc.Element("AAA").Elements("BBB");

You need to start getting the root element and then select the parent BBBs using Elements method:
var parentBbbs =xdoc.Element("AAA").Elements("BBB");

Just document.Root.Elements() should work.
Basically Descendants() recurses, whereas Elements() only gets direct children.

Get XML Node Text using LINQ To XML

Trying to get the value for the "title" node from this XML -> http://feeds.feedburner.com/dotnetshoutout-published
I am using this code:
var d = XDocument.Load("http://feeds.feedburner.com/dotnetshoutout-published");
var node = d.Root.Descendants().Where(x => x.Name == "title").FirstOrDefault();
Always returns null. Making me crazy, any assistance is appreciated.

I guess you have an Xml Namespace on your elements.If so, your element name won't be just title, it will be namespace + title.Instead you should check the LocalName :
var node = d.Root.Descendants().Where(x => x.LocalName == "title").FirstOrDefault();
Or, you can look at the namespace of your elements and create an XNamespace and use it to fetch elements:
XNamespace ns = "yournamespace";
var node = d.Root.Descendants(ns + "title").FirstOrDefault();
You can read the documentation to find more info about how to deal with xml namespaces.

XPathSelectElements returns null

Load function is already defined in xmlData class
public class XmlData
{
public void Load(XElement xDoc)
{
var id = xDoc.XPathSelectElements("//ID");
var listIds = xDoc.XPathSelectElements("/Lists//List/ListIDS/ListIDS");
}
}
I'm just calling the Load function from my end.
XmlData aXmlData = new XmlData();
string input, stringXML = "";
TextReader aTextReader = new StreamReader("D:\\test.xml");
while ((input = aTextReader.ReadLine()) != null)
{
stringXML += input;
}
XElement Content = XElement.Parse(stringXML);
aXmlData.Load(Content);
in load function,im getting both id and and listIds as null.
My test.xml contains
<SEARCH>
<ID>11242</ID>
<Lists>
<List CURRENT="true" AGGREGATEDCHANGED="false">
<ListIDS>
<ListID>100567</ListID>
<ListID>100564</ListID>
<ListID>100025</ListID>
<ListID>2</ListID>
<ListID>1</ListID>
</ListIDS>
</List>
</Lists>
</SEARCH>

EDIT: Your sample XML doesn't have an id element in the namespace with the nss alias. It would be <nss:id> in that case, or there'd be a default namespace set up. I've assumed for this answer that in reality the element you're looking for is in the namespace.
Your query is trying to find an element called id at the root level. To find all id elements, you need:
var tempId = xDoc.XPathSelectElements("//nss:id", ns);
... although personally I'd use:
XDocument doc = XDocument.Parse(...);
XNamespace nss = "http://schemas.microsoft.com/SQLServer/reporting/reportdesigner";
// Or use FirstOrDefault(), or whatever...
XElement idElement = doc.Descendants(nss + "id").Single();
(I prefer using the query methods on LINQ to XML types instead of XPath... I find it easier to avoid silly syntax errors etc.)
Your sample code is also unclear as you're using xDoc which hasn't been declared... it helps to write complete examples, ideally including everything required to compile and run as a console app.

I am looking at the question 3 hours after it was submitted and 41 minutes after it was (last) edited.
There are no namespaces defined in the provided XML document.
var listIds = xDoc.XPathSelectElements("/Lists//List/ListIDS/ListIDS");
This XPath expression obviously doesn't select any node from the provided XML document, because the XML document doesn't have a top element named Lists (the name of the actual top element is SEARCH)
var id = xDoc.XPathSelectElements("//ID");
in load function,im getting both id and and listIds as null.
This statement is false, because //ID selects the only element named ID in the provided XML document, thus the value of the C# variable id is non-null. Probably you didn't test thoroughly after editing the XML document.
Most probably the original ID element belonged to some namespace. But now it is in "no namespace" and the XPath expression above does select it.

string xmldocument = "<response xmlns:nss=\"http://schemas.microsoft.com/SQLServer/reporting/reportdesigner\"><action>test</action><id>1</id></response>";
XElement Content = XElement.Parse(xmldocument);
XPathNavigator navigator = Content.CreateNavigator();
XmlNamespaceManager ns = new XmlNamespaceManager(navigator.NameTable);
ns.AddNamespace("nss", "http://schemas.microsoft.com/SQLServer/reporting/reportdesigner");
var tempId = navigator.SelectSingleNode("/id");

The reason for the null value or system returned value is due to the following
var id = xDoc.XPathSelectElements("//ID");
XpathSElectElements is System.xml.linq.XElment which is linq queried date. It cannot be directly outputed as such.
To Get individual first match element
use XPathSelectElement("//ID");
You can check the number of occurrences using XPathSelectElements as
var count=xDoc.XPathSelectElements("//ID").count();
you can also query the linq statement as order by using specific conditions
Inorder to get node value from a list u can use this
foreach (XmlNode xNode in xDoc.SelectNodes("//ListIDS/ListID"))
{
Console.WriteLine(xNode.InnerText);
}
For Second list you havnt got the value since, the XPath for list items is not correct

LINQ to XML equivalent of XPath

I have code which parses XML that looks like this:
<custom_fields>
<custom_field>
<column_name>foo</column_name>
<column_value>0</column_value>
<description>Submitted</description>
<data_type>BOOLEAN</data_type>
<length>0</length>
<decimal>0</decimal>
</custom_field>
<custom_field>
<column_name>bar</column_name>
<column_value>0</column_value>
<description>Validated</description>
<data_type>BOOLEAN</data_type>
<length>0</length>
<decimal>0</decimal>
</custom_field>
</custom_fields>
... more <custom_field> elements...
I want to find the element called custom_field which has a child element called column_name with a certain value (for example bar), and then find that child's sibling called column_value and get its value. Right now I use XPath on an XMlDocument to do this:
string path = "//custom_fields/custom_field[column_name='" + key + "']";
XmlNode xNode = doc.SelectSingleNode(path);
if (xNode != null)
{
XmlNode v = xNode.SelectSingleNode("column_value");
val.SetValue(v.InnerText);
}
Where key is the name of the field I am looking for.
But I want to do this using the new LINQ to XML syntax on an XDocument. My thinking is that I will move much of my old-style XPath parsing to the LINQ methods. Maybe it's not a good idea, but this is a case where if I can get it to work, then I believe I will have a much better understanding of LINQ in general, and will be able to clean up a lot of complex code.

You can always use XPath within LINQ to XML. Just include the System.Xml.XPath namespace.
var xpath = $"//custom_fields/custom_field[column_name='{key}']/column_value";
var columnValue = doc.XPathSelectElement(xpath);
if (columnValue != null)
{
val.SetValue((int)columnValue);
}
Otherwise for the equivalent LINQ to XML query:
var columnValue = doc.Descendants("custom_fields")
.Elements("custom_field")
.Where(cf => (string)cf.Element("column_name") == key) // assuming `key` is a string
.Elements("column_value")
.SingleOrDefault();

Your XQuery expression
//custom_fields/custom_field[column_name='key']
selects all custom_field elements in custom_fields elements where the value of the column_key child element equals "key". You expect a single element to be returned and select the value of the column_value child element.
You can express this using LINQ to XML as follows:
var doc = XDocument.Load(...);
var query = from fields in doc.Descendants("custom_fields")
from field in fields.Elements("custom_field")
where (string)field.Element("column_name") == "key"
select (int)field.Element("column_value");
int result = query.Single();

I want to find the element called
custom_field which has a child element
called column_name with a certain
value (for example "bar", and then
find that child's sibling called
column_value and get its value.
Use:
/custom_fields/custom_field[column_name = 'bar']/column_value

Retrieve Element of XDocument by name

I have an XML document. I want to retrieve a specific descendant node of the root node. The root node does not have a namespace, however, the children nodes do, although they are all the same. What is the best way to retrieve this element as an element?

The namespace of the root node doesn't matter.
You can just write
XNamespace ns = "http://...";
var elem = doc.Element(ns + "TagName");

If you don't know the namespace of the children you could match them by LocalName, which refers to the local (unqualified) part of the name.
string name = "purchase";
var query = xml.Descendants()
.Where(e => e.Name.LocalName == name);
This returns an IEnumerable<XElement>. From there you can loop over it or use SingleOrDefault if you expect only one to exist.