Deleting nodes from XML file in C#

[markknowsley]

Using the following XML file as an example:

<?xml version='1.0'?>
<Collection>
   <Book Id='1'>
      <Title>Principle of Relativity</Title>
      <Author>Albert Einstein</Author>
      <Genre>Physics</Genre>
   </Book>
   <Book Id='2'>
      <Title>Cosmos</Title>
      <Author>Carl Sagan</Author>
      <Genre>Cosmology</Genre>
   </Book>
</Collection>

I want to write a C# method that will delete the Book node with the Id='2'.

I have the following code:

XmlDocument doc = new XmlDocument();
                doc.Load("test.xml");

                XmlNodeList nodeList = doc.SelectNodes("//Collection");
                foreach (XmlNode node in nodeList)
                {
                    node.RemoveChild(node.SelectSingleNode("Book"));
                }

                doc.PreserveWhitespace = true;
                XmlTextWriter writer = new XmlTextWriter("test.xml", Encoding.Unicode);
                doc.WriteTo(writer);
                writer.Close();

which removes the first node with the id 'Book'. Please can someone tell me how i can modify this to delete the node where Book Id='2'?

 

[jmeckley]

instead of cycling through each node look into xPath queries. this is the filter language for xml.

//define variables
string fileName = "test.xml";
int bookId = 2;
string xPathQuery = string.format("//Book[ID={0}]", bookId);

//open document
XmlDocument doc = new XmlDocument();
doc.Load(fileName);

//remove node
XmlNode nodeToDelete = doc.SelectSingleNode(xPathQuery);
doc.RemoveChild(nodetoDelete);

//save
doc.PreserveWhitespace = true;
doc.Save(fileName);

Jason Meckley
Programmer
Specialty Bakers, Inc.

 

[matt23lucier]

Instead of using:
node.RemoveChild(node.SelectSingleNode("Book"));
Try:
node.RemoveChild(node.SelectSingleNode("//Book[@Id='2']"));

 

[markknowsley]

Next question: I have some XML in this format

<employee ID="000001" Initials="G" Surname="RUSEDSKI                           ">
		<summary batchnumber="00841" batchitem="01" claimmonth="1" claimyear="2007" 		

Miles="154" amount="27.72" AuthStatus="Rejected" vmodifiedby="" vnotes=""/>
	</employee>
	<employee ID="000014" Initials="T" Surname="HENMAN                           ">
		<summary batchnumber="00841" batchitem="02" claimmonth="1" claimyear="2007" 		

Miles="24" amount="10.18" AuthStatus="Rejected" vmodifiedby="" vnotes=""/>
	</employee>

I've loaded the XML, created an XMLNodeList and then iterated through;

foreach (XmlNode node in nodeList)
{
node.RemoveChild(node.SelectSingleNode("//summary[@batchnumber='00841']);
}

This works fine and gets rid of the two nodes. However, I want to delete XML based on the value of the AuthStatus field - if this is set to 'Approved' then I want to delete the node.

But if I change the XPath to @authstatus='Approved' I get an 'Object Reference not set to an instance of an Object' error. Can someone tell me why this is?

Mark.