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XDocument Descendant Selector using Wildcard?

I have some XML structured like this:
<form>
<section-1>
<item-1>
<value />
</item-1>
<item-2>
<value />
</item-2>
</section-1>
<section-2>
<item-3>
<value />
</item-3>
<item-4>
<value />
</item-4>
</section-2>
</form>
...and want to turn it into something sane like this:
<form>
<items>
<item id="1">
<value/>
</item>
<item id="2">
<value/>
</item>
<item id="3">
<value/>
</item>
<item id="4">
<value/>
</item>
</items>
</form>
I am struggling to turn the old XML into an array or object of values. Once in the new format I'd be able to do the following:
XDocument foo = XDocument.Load(form.xml);
var items = foo.Descendants("item")
.Select(i => new Item
{
value = i.Element("value").Value
});
...but in the current mess the xml is in can I wildcard the descendants selector?
var items = foo.Descendants("item"*)
...or something? I tried to follow this question's answer but failed to adapt it to my purpose.

Ah-ha! It did click in the end. If I leave the descendants selector blank and add in a where statement along the lines of what's in this question's answer
.Where(d => d.Name.ToString().StartsWith("item-"))
Then we get:
XDocument foo = XDocument.Load(form.xml);
var items = foo.Descendants()
.Where(d => d.Name.ToString().StartsWith("item-"))
.Select(i => new Item
{
value = i.Element("value").Value
});
...and I'm now able to iterate through those values while outputting the new XML format. Happiness.

How to get elements without child elements?

Here is my xml:
<Root>
<FirstChild id="1" att="a">
<SecondChild id="11" att="aa">
<ThirdChild>123</ThirdChild>
<ThirdChild>456</ThirdChild>
<ThirdChild>789</ThirdChild>
</SecondChild>
<SecondChild id="12" att="ab">12</SecondChild>
<SecondChild id="13" att="ac">13</SecondChild>
</FirstChild>
<FirstChild id="2" att="b">2</FirstChild>
<FirstChild id="3" att="c">3</FirstChild>
</Root>
This xml doc is very big and may be 1 GB size or more. For better performance in querying, i want to read xml doc step by step. So, in first step i want to read only "First Child"s and their attributes like below:
<FirstChild id="1" att="a"></FirstChild>
<FirstChild id="2" att="b">2</FirstChild>
<FirstChild id="3" att="c">3</FirstChild>
And after that, I maybe want to get "SecondChild"s by id of their parent and so ...
<SecondChild id="11" att="aa"></SecondChild>
<SecondChild id="12" att="ab">12</SecondChild>
<SecondChild id="13" att="ac">13</SecondChild>
How can I do it?
Note: XDoc.Descendants() or XDoc.Elements() load all specific elements with all child elements!

Provided that you have memory available to hold the file, I suggest treating each search step as an item in the outer collection of a PLINQ pipeline.
I would start with an XName collection for the node collections that you want to retrieve. By nesting queries within XElement constructors, you can return new instances of your target nodes, with only name and attribute information.
With a .Where(...) statement or two, you could also filter the attributes being kept, allow for some child nodes to be retained, etc.
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
namespace LinqToXmlExample
{
public class Program
{
public static void Main(string[] args)
{
XElement root = XElement.Load("[your file path here]");
XName[] names = new XName[] { "firstChild", "secondChild", "thirdChild" };
IEnumerable<XElement> elements =
names.AsParallel()
.Select(
name =>
new XElement(
$"result_{name}",
root.Descendants(name)
.AsParallel()
.Select(
x => new XElement(name, x.Attributes()))))
.ToArray();
}
}
}

I suggest creating a new element and copy the attributes.
var sourceElement = ...get "<FirstChild id="1" att="a">...</FirstChild>" through looping, xpath or any method.
var element = new XElement(sourceElement.Name);
foreach( var attribute in sourceElement.Attributes()){
element.Add(new XAttribute(attribute.Name, attribute.Value));
}

In VB this you could do this to get a list of FirstChild
'Dim yourpath As String = "your path here"
Dim xe As XElement
'to load from a file
'xe = XElement.Load(yourpath)
'for testing
xe = <Root>
<FirstChild id="1" att="a">
<SecondChild id="11" att="aa">
<ThirdChild>123</ThirdChild>
<ThirdChild>456</ThirdChild>
<ThirdChild>789</ThirdChild>
</SecondChild>
<SecondChild id="12" att="ab">12</SecondChild>
<SecondChild id="13" att="ac">13</SecondChild>
</FirstChild>
<FirstChild id="2" att="b">2</FirstChild>
<FirstChild id="3" att="c">3</FirstChild>
</Root>
Dim ie As IEnumerable(Of XElement)
ie = xe...<FirstChild>.Select(Function(el)
'create a copy
Dim foo As New XElement(el)
foo.RemoveNodes()
Return foo
End Function)

Change XML element value in c#

My C# code:
XDocument doc = XDocument.Load(filename);
IEnumerable<XElement> collection =
doc.Elements("BCIRequest").Elements("Card").Elements("SelectedPIN");
My XML document:
<?xml version="1.0" encoding="utf-8"?>
<BCIRequest Version="2.0"
xmlns="urn:xxxxxx:bci:request">
<Header>
<SenderCode>XX99</SenderCode>
<SenderID>9999</SenderID>
<SequenceNumber>123</SequenceNumber>
<CardGroupCount>2</CardGroupCount>
<CardCount>4</CardCount>
<BlockCount>2</BlockCount>
</Header>
<!--card groups (must precede cards and blocks)-->
<CardGroup RequestID="1">
<CustomerNumber>XX01234567</CustomerNumber>
<CardGroupName Emboss="true">GROUP ONE</CardGroupName>
</CardGroup>
<CardGroup RequestID="2"
RequestRef="87416CB7-DAEF-483A-BD08-1A885531D958">
<CustomerNumber>XX12345678</CustomerNumber>
<CardGroupName Emboss="false">GROUP TWO</CardGroupName>
</CardGroup>
<Card RequestID="3">
<CustomerNumber>XX01234567</CustomerNumber>
<DriverCard>
<Driver Emboss="true">MARGE SIMPSON</Driver>
</DriverCard>
<CardTypeID>10</CardTypeID>
<PurchaseCategoryID>11</PurchaseCategoryID>
<Reissue>false</Reissue>
<GeneratedPIN/>
<OdoPrompt>false</OdoPrompt>
<CRNPrompt>false</CRNPrompt>
</Card>
<Card RequestID="4">
<CustomerNumber>XX12345678</CustomerNumber>
<VehicleCard>
<VRN Emboss="true">KYI 830</VRN>
</VehicleCard>
<CardTypeID>10</CardTypeID>
<PurchaseCategoryID>11</PurchaseCategoryID>
<Reissue>false</Reissue>
<SelectedPIN>0123</SelectedPIN>
<OdoPrompt>false</OdoPrompt>
<CRNPrompt>false</CRNPrompt>
</Card>
<Card RequestID="5">
<CustomerNumber>XX01234567</CustomerNumber>
<BearerCard>
<Bearer Emboss="true">OPEN XXXXXX</Bearer>
</BearerCard>
<CardTypeID>10</CardTypeID>
<PurchaseCategoryID>11</PurchaseCategoryID>
<Reissue>false</Reissue>
<FleetPIN/>
<OdoPrompt>false</OdoPrompt>
<CRNPrompt>false</CRNPrompt>
</Card>
<Block RequestID="6">
<CustomerNumber>XX01234567</CustomerNumber>
<PAN>7002999999999999991</PAN>
</Block>
<Card RequestID="7"
RequestRef="956EA6C5-7D7E-4622-94D0-38CAD9FCC8DF">
<CustomerNumber>XX01234567</CustomerNumber>
<DriverCard>
<Driver Emboss="true">HOMER SIMPSON</Driver>
<VRN Emboss="true">795 DVI</VRN>
</DriverCard>
<EmbossText>SPRINGFIELD POWER</EmbossText>
<CardTypeID>10</CardTypeID>
<TokenTypeID>20</TokenTypeID>
<PurchaseCategoryID>30</PurchaseCategoryID>
<ExpiryDate>2018-12</ExpiryDate>
<Reissue>true</Reissue>
<SelectedPIN>0123</SelectedPIN>
<OdoPrompt>true</OdoPrompt>
<CRNPrompt>true</CRNPrompt>
<!--address with optional fields specified-->
<CardDeliveryAddress OneTimeUse="false">
<ContactName>M xxxx</ContactName>
<ContactTitle>Mr</ContactTitle>
<CompanyName>Sxxxx</CompanyName>
<Line1>Sector 22-F</Line1>
<Line2>Springfield Power Plant</Line2>
<Line3>xxx Road</Line3>
<City>xxxx</City>
<Zipcode>xxxx</Zipcode>
<CountryCode>xxx</CountryCode>
</CardDeliveryAddress>
<!--address with only required fields-->
<PINDeliveryAddress OneTimeUse="true">
<Line1>xxxx</Line1>
<City>xxx</City>
<Zipcode>xxxx</Zipcode>
<CountryCode>xxxx</CountryCode>
</PINDeliveryAddress>
<Limits>
<Value Transaction="unlimited" Daily="200" Weekly="unlimited" Monthly="400"/>
<Volume Transaction="100" Daily="unlimited" Weekly="unlimited" Monthly="unlimited"/>
<Transactions Daily="unlimited" Weekly="unlimited" Monthly="unlimited"/>
<Day Monday="true" Tuesday="true" Wednesday="true" Thursday="true" Friday="true" Saturday="false" Sunday="false"/>
<Time Start="unlimited" End="17:00:00"/>
</Limits>
<Products>
<FuelProductRestrictionID>40</FuelProductRestrictionID>
<NonFuelProductRestrictionID>51</NonFuelProductRestrictionID>
<NonFuelProductRestrictionID>52</NonFuelProductRestrictionID>
<NonFuelProductRestrictionID>53</NonFuelProductRestrictionID>
<NonFuelProductRestrictionID>54</NonFuelProductRestrictionID>
<NonFuelProductRestrictionID>55</NonFuelProductRestrictionID>
</Products>
</Card>
<Block RequestID="8"
RequestRef="69A3E44D-DC10-4BEE-9249-1FC3C651BA0E">
<CustomerNumber>xxxxx</CustomerNumber>
<PAN>xxxxxx</PAN>
</Block>
</BCIRequest>
I need to update the element value in the above values. The old value is:
<SelectedPIN>0123</SelectedPIN>
And the new value should be:
<SelectedPIN EncryptedPIN="TKDS" FormNumber="000793906306">****</SelectedPIN>
Can anyone can help me on this?
If I selected the BCIRequest element, it's returning a null value. I've tried many solutions but unable to get one working on this XML file.

There many ways an Xml can be be modified, I prefer XDocument
XDocument doc = XDocument.Parse(input);
foreach (var element in doc.Descendants("SelectedPIN")) // filter if you want single element, in example I modifed for all elements.
{
element.Add(new XAttribute("EncryptedPIN", "TKDS"));
element.Add(new XAttribute("FormNumber", "000793906306"));
element.Value = "xxxxx"; //new value
}
and finally you can save the document using
doc.Save();
Take a look at this Demo

The root node (BCIRequest) contains a namespace so you need to include that into your query. Something like this should work:
XNamespace ns = "urn:xxxxxx:bci:request";
IEnumerable<XElement> collection = doc.Elements(ns + "BCIRequest").Elements(ns + "Card").Elements(ns + "SelectedPIN");

Remove all nodes in a specified namespace from XML

I have an XML document that contains some content in a namespace. Here is an example:
<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:test="urn:my-test-urn">
<Item name="Item one">
<test:AlternativeName>Another name</test:AlternativeName>
<Price test:Currency="GBP">124.00</Price>
</Item>
</root>
I want to remove all of the content that is within the test namespace - not just remove the namespace prefix from the tags, but actually remove all nodes (elements and attributes) from the document that (in this example) are in the test namespace. My required output is:
<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:test="urn:my-test-urn">
<Item name="Item one">
<Price>124.00</Price>
</Item>
</root>
I'm currently not overly concerned if the namespace declaration is still present, for now I'd be happy with removing just the content within the specified namespace. Note that there may be multiple namespaces in the document to be modified, so I'd like to be able to specify which one I want to have the content removed.
I've tried doing it using .Descendants().Where(e => e.Name.Namespace == "test") but that is only for returning an IEnumerable<XElement> so it doesn't help me with finding the attributes, and if I use .DescendantNodes() I can't see a way of querying the namespace prefix as that doesn't seem to be a property on XNode.
I can iterate through each element and then through each attribute on the element checking each one's Name.Namespace but that seems inelegant and hard to read.
Is there a way of achieving this using LINQ to Xml?

Iterating through elements then through attributes seems not too hard to read :
var xml = #"<?xml version='1.0' encoding='UTF-8'?>
<root xmlns:test='urn:my-test-urn'>
<Item name='Item one'>
<test:AlternativeName>Another name</test:AlternativeName>
<Price test:Currency='GBP'>124.00</Price>
</Item>
</root>";
var doc = XDocument.Parse(xml);
XNamespace test = "urn:my-test-urn";
//get all elements in specific namespace and remove
doc.Descendants()
.Where(o => o.Name.Namespace == test)
.Remove();
//get all attributes in specific namespace and remove
doc.Descendants()
.Attributes()
.Where(o => o.Name.Namespace == test)
.Remove();
//print result
Console.WriteLine(doc.ToString());
output :
<root xmlns:test="urn:my-test-urn">
<Item name="Item one">
<Price>124.00</Price>
</Item>
</root>

Give this a try. I had to pull the namespace from the root element then run two separate Linqs:
Removes elements with the namespace
Removes attributes with the namespace
Code:
string xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" +
"<root xmlns:test=\"urn:my-test-urn\">" +
"<Item name=\"Item one\">" +
"<test:AlternativeName>Another name</test:AlternativeName>" +
"<Price test:Currency=\"GBP\">124.00</Price>" +
"</Item>" +
"</root>";
XDocument xDocument = XDocument.Parse(xml);
if (xDocument.Root != null)
{
string namespaceValue = xDocument.Root.Attributes().Where(a => a.IsNamespaceDeclaration).FirstOrDefault().Value;
// Removes elements with the namespace
xDocument.Root.Descendants().Where(d => d.Name.Namespace == namespaceValue).Remove();
// Removes attributes with the namespace
xDocument.Root.Descendants().ToList().ForEach(d => d.Attributes().Where(a => a.Name.Namespace == namespaceValue).Remove());
Console.WriteLine(xDocument.ToString());
}
Results:
<root xmlns:test="urn:my-test-urn">
<Item name="Item one">
<Price>124.00</Price>
</Item>
</root>
If you want to remove the namespace from the root element add the this line in the if statement after you get the namespaceValue
xDocument.Root.Attributes().Where(a => a.IsNamespaceDeclaration).Remove();
Results:
<root>
<Item name="Item one">
<Price>124.00</Price>
</Item>
</root>

How retrieve deeper siblings using LINQ to XML?

I have an XML structure as follows. I need to extract "Value" and "String" by matching the command attributes? How to write LINQ for this?
<Root>
<Command val="1001" type="sync">
<Status>
<DataList>
<Info>
<Value>1</Value>
<String>Sample String 1 is set</String>
</Info>
<Info>
<Value>2</Value>
<String>Sample String 2 is set</String>
</Info>
<Info>
<Value>3</Value>
<String>Sample String 3 is set</String>
</Info>
</DataList>
</Status>
<Command>
</Root>
I tried something as below but exception occurred while running.
lst = (
from command in xmlDoc.Descendants("Command")
.Descendants("Status")
.Descendants("DataList")
select new EnumList
{
val = command.Element("Value").Value,
stringVal = command.Element("String").Value,
})
.ToList();

Try
lst = (
from command in xmlDoc.Descendants("Info")
select new EnumList
{
val = command.Element("Value").Value,
stringVal = command.Element("String").Value,
})
.ToList();
and you have error in xml sample (no close tag Command), change it to
</Command>
</Root>