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Search through XML and grab another Node

<?xml version="1.0" encoding="UTF-8"?>
<Envelope xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Message>
<MessageID>1</MessageID>
<Product>
<SKU>33333-01</SKU>
</Product>
</Message>
</Envelope>
I've tried googling but whether I'm just not providing the correct search criteria I don't know.
I want to be able to search the XML file based on the MessageID and then grab the SKU.
I then want to search another XML file based on the SKU and remove that message completely.
<?xml version="1.0" encoding="UTF-8"?>
<Envelope xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Message>
<MessageID>1</MessageID>
<Inventory>
<SKU>33333-01</SKU>
<Quantity>1</Quantity>
</Inventory>
</Message>
<Message>
<MessageID>2</MessageID>
<Inventory>
<SKU>22222-01</SKU>
<Quantity>1</Quantity>
</Inventory>
</Message>
</Envelope>
Meaning the XML above becomes:
<?xml version="1.0" encoding="UTF-8"?>
<Envelope xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Message>
<MessageID>2</MessageID>
<Inventory>
<SKU>22222-01</SKU>
<Quantity>1</Quantity>
</Inventory>
</Message>
</Envelope>
To confirm I cannot confirm that the MessageID will be the same over different XML files.
Thanks in advance for any help.
My questions:
How do I search through XML files?
How do I then grab another Nodes details
Can I remove a complete from an XML file based on a search?

You can use XmlDocument to load your XML document. Then, you can use XPath for searching any nodes.
XmlDocument document = new XmlDocument();
document.Load("C:\fileOnTheDisk.xml");
// or
document.LoadXml("<a>someXmlString</a>");
// Returns single element or null if not found
var singleNode = document.SelectSingleNode("Envelope/Message[MessageID = '1']");
// Returns a NodeList
var nodesList = document.SelectNodes("Envelope/Message[MessageID = '1']");
Read more about XPath at w3schools.com.
Here is a good XPath Tester.
For example, you can use the following XPath to find nodes in your document by ID:
XmlDocument document = new XmlDocument();
document.Load("C:\doc.xml");
var node = document.SelectSingleNode("Envelope/Message[MessageID = '1']");
var sku = node.SelectSingleNode("Inventory/SKU").InnerText;
Console.WriteLine("{0} node has SKU = {1}", 1, sku);
Or you can output all SKUs:
foreach (XmlNode node in document.SelectNodes("Envelope/Message"))
{
Console.WriteLine("{0} node has SKU = {1}",
node.SelectSingleNode("MessageID").InnerText,
node.SelectSingleNode("Inventory/SKU").InnerText);
}
It will produce:
1 node has SKU = 33333-01
2 node has SKU = 22222-01
Note that there are possible NullReferenceExceptions if nodes are not present.
You can simply remove it using RemoveChild() method of its parent.
XmlDocument document = new XmlDocument();
document.Load("C:\doc.xml");
var node = document.SelectSingleNode("Envelope/Message[MessageID = '1']");
node.ParentNode.RemoveChild(node);
document.Save("C:\docNew.xml"); // will be without Message 1

You can use Linq to XML to do this:
var doc= XDocument.Load("input.xml");//path of your xml file in which you want to search based on message id.
var searchNode= doc.Descendants("MessageID").FirstOrDefault(d => d.Value == "1");// It will search message node where its value is 1 and get first of it
if(searchNode!=null)
{
var SKU=searchNode.Parent.Descendants("SKU").FirstOrDefault();
if(SKU!=null)
{
var searchDoc=XDocument.Load("search.xml");//path of xml file where you want to search based on SKU value.
var nodes =searchDoc.Descendants("SKU").Where(d=>d.Value==SKU.Value).Select(d=>d.Parent.Parent).ToList();
nodes.ForEach(node=>node.Remove());
searchDoc.Save("output.xml");//path of output file
}
}

I'd recommend you did this using LINQ to XML - it's much nicer to work with than the old XmlDocument API.
For all the examples, you can parse your XML string xml to an XDocument like so:
var doc = XDocument.Parse(xml);
1. How do I search through XML files?
You can get the SKU for a specific message ID by querying your document:
var sku = (string)doc.Descendants("Message")
.Where(e => (int)e.Element("MessageID") == 1)
.SelectMany(e => e.Descendants("SKU"))
.Single();
2. How do I then grab another Nodes details?
You can get the Message element with a specified SKU using a another query:
var message = doc.Descendants("SKU")
.Where(sku => (string)sku == "33333-01")
.SelectMany(e => e.Ancestors("Message"))
.Single();
3. Can I remove a complete element from an XML file based on a search?
Using your result from step 2, you can simple call Remove:
message.Remove();
Alternatively, you can combine the query from step 2 and simply execute a command to remove any messages that have a specific SKU:
doc.Descendants("SKU")
.Where(sku => (string)sku == "33333-01")
.SelectMany(e => e.Ancestors("Message"))
.Remove();

I tried to answer all your questions:
using System.Xml.XPath;
using System.Xml.Linq;
XDocument xdoc1 = XDocument.Load("xml1.xml");
XDocument xdoc2 = XDocument.Load("xml2.xml");
string sku = String.Empty;
string searchedID = "2";
//1.searching through an xml file based on path
foreach (XElement message in xdoc1.XPathSelectElements("Envelope/Message"))
{
if (message.Element("MessageID").Value.Equals(searchedID))
{
//2.grabbing another node's details
sku = message.XPathSelectElement("Inventory/SKU").Value;
}
}
foreach (XElement message in xdoc2.XPathSelectElements("Envelope/Message"))
{
if (message.XPathSelectElement("Inventory/SKU") != null && message.XPathSelectElement("Inventory/SKU").Value.Equals(sku))
{
//removing a node
message.Remove();
}
}
xdoc2.Save("xml2_del.xml");
}

Xelement - get elements

I'm loading an xml feed from youtube into xelement like so:
XElement element = XElement.Load(url);
This is fine and I get a document that looks like this:
<?xml version='1.0' encoding='UTF-8' ?>
<feed xmlns='http://www.w3.org/2005/Atom' xmlns:media='http://search.yahoo.com/mrss/' xmlns:opensearch='http://a9.com/-/spec/opensearchrss/1.0/' xmlns:gd='http://schemas.google.com/g/2005' xmlns:yt='http://gdata.youtube.com/schemas/2007'>
<id>http://gdata.youtube.com/feeds/api/users/id/uploads</id>
<updated>2014-01-07T11:43:08.269Z</updated>
<category scheme='http://schemas.google.com/g/2005#kind' term='http://gdata.youtube.com/schemas/2007#video'/>
<title type='text'>Uploads by id</title>
<logo>http://www.gstatic.com/youtube/img/logo.png</logo>
<link rel='related' type='application/atom+xml' href='https://gdata.youtube.com/feeds/api/users/stonemarketuk'/>
<link rel='alternate' type='text/html' href='https://www.youtube.com/channel/333/videos'/>
<link rel='http://schemas.google.com/g/2005#feed' type='application/atom+xml' href='https://gdata.youtube.com/feeds/api/users/id/uploads'/>
<link rel='http://schemas.google.com/g/2005#batch' type='application/atom+xml' href='https://gdata.youtube.com/feeds/api/users/id/uploads/batch'/>
<link rel='self' type='application/atom+xml' href='https://gdata.youtube.com/feeds/api/users/id/uploads?start-index=1&max-results=25'/>
<link rel='next' type='application/atom+xml' href='https://gdata.youtube.com/feeds/api/users/id/uploads?start-index=26&max-results=25'/>
<author>
<name>StonemarketUK</name>
<uri>https://gdata.youtube.com/feeds/api/users/id</uri>
</author>
<generator version='2.1' uri='http://gdata.youtube.com'>YouTube data API</generator>
<openSearch:totalResults>30</openSearch:totalResults>
<openSearch:startIndex>1</openSearch:startIndex>
<openSearch:itemsPerPage>25</openSearch:itemsPerPage>
<entry>
....entry elements
</entry>
<entry>
....entry elements
</entry>
</feed>
How do I get the entry elements? I have tried the following:
var entries = element.Elements("entry");
var entries = element.Element("feed").Elements("entry");
var entries = element.Nodes().Elements("entry");
But none of these return anything
I also debugged and tried element.Elements().FirstOrDefault() but this returned null. element.Nodes().Count() returned 41 so should I be trying to get the nodes called entry?

All elements are in a namespace (xmlns='http://www.w3.org/2005/Atom'). You must declare the atom namespace and use it.
It's easy:
XNamespace atom = "http://www.w3.org/2005/Atom";
var xml = XElement.Load(url);
var entry = xml.Elements(atom + "entry");
etc.
An easy way to get the right Element name is using XName.Get(). If you only have one namespace, you could put it in a seperate function:
internal static XName GetXName(string name)
{
string atomNamespace = "http://www.w3.org/2005/Atom";
return XName.Get(name, atomNamespace);
}

Try the following
var entryList = element.Elements().Where(x => x.Name.LocalName == "entry");
The problem here is that every element without an explicit namespace is implicitly in the namespace "http://www.w3.org/2005/Atom". The LocalName property can still be used to access the simple name as shown above. Barring that you need to construct a proper XName element which includes this namespace in order to match the 'entry' nodes

Getting an XElement with a namespace via XPathSelectElements

I have an XML e.g.
<?xml version="1.0" encoding="utf-8"?>
<A1>
<B2>
<C3 id="1">
<D7>
<E5 id="abc" />
</D7>
<D4 id="1">
<E5 id="abc" />
</D4>
<D4 id="2">
<E5 id="abc" />
</D4>
</C3>
</B2>
</A1>
This is may sample code:
var xDoc = XDocument.Load("Test.xml");
string xPath = "//B2/C3/D4";
//or string xPath = "//B2/C3/D4[#id='1']";
var eleList = xDoc.XPathSelectElements(xPath).ToList();
foreach (var xElement in eleList)
{
Console.WriteLine(xElement);
}
It works perfectly, but if I add a namespace to the root node A1, this code doesn't work.
Upon searching for solutions, I found this one, but it uses the Descendants() method to query the XML. From my understanding, this solution would fail if I was searching for <E5> because the same tag exists for <D7>, <D4 id="1"> and <D4 id="2">
My requirement is to search if a node exists at a particular XPath. If there is a way of doing this using Descendants, I'd be delighted to use it. If not, please guide me on how to search using the name space.
My apologies in case this is a duplicate.

To keep using XPath, you can use something link this:
var xDoc = XDocument.Parse(#"<?xml version='1.0' encoding='utf-8'?>
<A1 xmlns='urn:sample'>
<B2>
<C3 id='1'>
<D7><E5 id='abc' /></D7>
<D4 id='1'><E5 id='abc' /></D4>
<D4 id='2'><E5 id='abc' /></D4>
</C3>
</B2>
</A1>");
// Notice this
XmlNamespaceManager nsmgr = new XmlNamespaceManager(new NameTable());
nsmgr.AddNamespace("sample", "urn:sample");
string xPath = "//sample:B2/sample:C3/sample:D4";
var eleList = xDoc.XPathSelectElements(xPath, nsmgr).ToList();
foreach (var xElement in eleList)
{
Console.WriteLine(xElement);
}

but it uses the Descendants() method to query the XML. From my understanding, this solution would fail if I was searching for because the same tag exists for , and
I'm pretty sure you're not quite understanding how that works. From the MSDN documentation:
Returns a filtered collection of the descendant elements for this document or element, in document order. Only elements that have a matching XName are included in the collection.
So in your case, just do this:
xDoc.RootNode
.Descendants("E5")
.Where(n => n.Parent.Name.LocalName == "B4");

Try this
var xDoc = XDocument.Parse("<A1><B2><C3 id=\"1\"><D7><E5 id=\"abc\" /></D7><D4 id=\"1\"><E5 id=\"abc\" /></D4><D4 id=\"2\"><E5 id=\"abc\" /></D4></C3></B2></A1>");
foreach (XElement item in xDoc.Element("A1").Elements("B2").Elements("C3").Elements("D4"))
{
Console.WriteLine(item.Element("E5").Value);//to get the value of E5
Console.WriteLine(item.Element("E5").Attribute("id").Value);//to get the value of attribute
}

reading node from xml file in XMLDocument

i am trying to grab the TopicName how should i go after it and try different combination but somehow i am unable to get TopicName below is my source codee...
XmlDocument xdoc = new XmlDocument();//xml doc used for xml parsing
xdoc.Load(
"http://latestpackagingnews.blogspot.com/feeds/posts/default"
);//loading XML in xml doc
XmlNodeList xNodelst = xdoc.DocumentElement.SelectNodes("content");//reading node so that we can traverse thorugh the XML
foreach (XmlNode xNode in xNodelst)//traversing XML
{
//litFeed.Text += "read";
}
sample xml file
<content type="application/xml">
<CatalogItems xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="sitename.xsd">
<CatalogSource Acronym="ABC" OrganizationName="ABC Corporation" />
<CatalogItem Id="3212" CatalogUrl="urlname">
<ContentItem xmlns:content="sitename.xsd" TargetUrl="url">
<content:SelectionSpec ClassList="" ElementList="" />
<content:Language Value="eng" Scheme="ISO 639-2" />
<content:Source Acronym="ABC" OrganizationName="ABC Corporation" />
<content:Topics Scheme="ABC">
<content:Topic TopicName="Marketing" />
<content:Topic TopiccName="Coverage" />
</content:Topics>
</ContentItem>
</CatalogItem>
</CatalogItems>
</content>

The Topic nodes in your XML are using the content namespace - you need to declare and use the XML namespace in your code, then you can use SelectNodes() to grab the nodes of interest - this worked for me:
XmlNamespaceManager nsmgr = new XmlNamespaceManager(xdoc.NameTable);
nsmgr.AddNamespace("content", "sitename.xsd");
var topicNodes = xdoc.SelectNodes("//content:Topic", nsmgr);
foreach (XmlNode node in topicNodes)
{
string topic = node.Attributes["TopicName"].Value;
}
Just as a comparison see how easy this would be with Linq to XML:
XDocument xdoc = XDocument.Load("test.xml");
XNamespace ns = "sitename.xsd";
string topic = xdoc.Descendants(ns + "Topic")
.Select(x => (string)x.Attribute("TopicName"))
.FirstOrDefault();
To get all topics you can replace the last statement with:
var topics = xdoc.Descendants(ns + "Topic")
.Select(x => (string)x.Attribute("TopicName"))
.ToList();

If you just need a specific element, then I'd use XPath:
This is a guide to use XPath in C#:
http://www.codeproject.com/KB/XML/usingXPathNavigator.aspx
And this is the query that will get you a collection of your Topics:
//content/CatalogItems/CatalogItem/ContentItem/content:Topics/content:Topic
You could tweak this query depending on what it is you're trying to accomplish, grabbing just a specific TopicName value:
//content/CatalogItems/CatalogItem/ContentItem/content:Topics/content:Topic/#TopicName
XPath is pretty easy to learn. I've done stuff like this pretty quickly with no prior knowledge.
You can paste you XML and xpath query here to test your queries:
http://www.bit-101.com/xpath/

The following quick and dirty LINQ to XML code obtains your TopicNames and prints them on the console.
XDocument lDoc = XDocument.Load(lXmlDocUri);
foreach (var lElement in lDoc.Element("content").Element(XName.Get("CatalogItems", "sitename.xsd")).Elements(XName.Get("CatalogItem", "sitename.xsd")))
{
foreach (var lContentTopic in lElement.Element(XName.Get("ContentItem", "sitename.xsd")).Element(XName.Get("Topics", "sitename.xsd")).Elements(XName.Get("Topic", "sitename.xsd")))
{
string lTitle = lContentTopic.Attribute("TopicName").Value;
Console.WriteLine(lTitle);
}
}
It'd have been a lot shorter if it wasn't for all the namespaces :) (Instead of "XName.Get" you would just use the name of the element).

How to get the value of an XML attribute?

I have a XML file:
<SourceMessage xmlns="test.test">
<updated>2011</updated>
<title type="p1"/>
<title type="p2"/>
<title type="p3"/>
<entry>
</entry>
</SourceMessage>
How could I use LINQ to get the <type> attribute of the <title> element, i.e. "p1", "p2" and "p3"?

Use XDocument.Load or XDocument.Parse to load the XML data into an XDocument. Then, using LINQ, you can get the type for each <title> element under the document root as follows:
XNamespace test = "test.test";
XDocument doc = XDocument.Load(file);
// - or -
XDocument doc = XDocument.Parse("<SourceMessage ...");
IEnumerable<string> query = from title in doc.Root.Elements(test + "title")
select (string)title.Attribute("type");
foreach (string item in query)
{
Console.WriteLine(item);
}
Output:
p1
p2
p3

var xElement XElement.Parse(xmlString);
var result = xElement.Descendants("title")
.Select(e => e.Attribute("type").Value);

XDocument xml = XDocument.Parse (#"<SourceMessage xmlns="test.test">
<updated>2011</updated>
<title type="p1"/>
<title type="p2"/>
<title type="p3"/>
<entry>
</entry>
</SourceMessage>");
foreach (var t in xml.Root.Descendants("title"))
Console.Write(t.Attribute("type").Value);