Appending an existing XML file with XmlWriter

Question

I've used the following code to create an XML file:

XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
xmlWriterSettings.Indent = true;
xmlWriterSettings.NewLineOnAttributes = true;
using (XmlWriter xmlWriter = XmlWriter.Create("Test.xml", xmlWriterSettings))
{
   xmlWriter.WriteStartDocument();
   xmlWriter.WriteStartElement("School");
   xmlWriter.WriteEndElement();
   xmlWriter.WriteEndDocument();
   xmlWriter.Close();
 }

I need to insert nodes dynamically creating the following structure:

<?xml version="1.0" encoding="utf-8"?>
<School />
   <Student>
      <FirstName>David</FirstName>
      <LastName>Smith</LastName>
   </Student>
   ...
   <Teacher>
      <FirstName>David</FirstName>
      <LastName>Smith</LastName>
   </Teacher>
   ...
</School>

How can I do it? The values of "FirstName" and "LastName" should be read from the keyboard and the values ​​can be entered at any time, of course under existing.

Answer 1

I have a suggestion for the next time:

string nameFile = "Test.xml";
bool newFile = false;


if (!File.Exists(nameFile))
{
    newFile = true;
    XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
    xmlWriterSettings.Indent = true;
    xmlWriterSettings.NewLineOnAttributes = true;

    xmlWriter.WriteStartDocument();
    xmlWriter.WriteStartElement("School");

    xmlWriter = XmlWriter.Create("Test.xml", xmlWriterSettings))
}
else
{
    doc = new XmlDocument();
    doc.Load(nameFile);

    // Create a XPathNavigator
    // You can go where you want to add
    // In this case it is just after last child of the roor
    XPathNavigator navigator = doc.CreateNavigator();     

    navigator.MoveToChild("School", "");
    xmlWriter = navigator.AppendChild();
}

// From here you can work only with xmlWriter,
// One will point on a file and the other on the stream of xmlDocument
// So you will need to save the document in the second choise

xmlWriter.WriteStartElement("Student");
xmlWriter.WriteElementString("FirstName", firstName);
xmlWriter.WriteElementString("LastName", lastName);
xmlWriter.WriteEndElement();


// End document / close or save. 
if (newFile)
    xmlWriter.WriteEndDocument();

xmlWriter.Close();

if (!newFile)
    doc.Save(nameFile);

It should work. :)