How do you update a XML file in C#

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C#

XML

Visual-Studio

LINQ

Greetings,

I am new to C# and XML coding. I have read a few tutorials online about how to deal with XML files. Currently I have a setup that creates an XML file with a few products that are being saved. I would like to read the file that has already been created, add another product to it and then save it but currently my code only overwrites what I have. Does anyone know of the way to add on to an XML file when trying to write to it. Here's the example of my XML file.

<table> 
   -<part> 
       <product_name>Test</product_name> 
       <length>10</length> <width>8</width> 
       <thickness>1.5</thickness> 
       <offset>.25</offset> 
       <yelements>6</yelements> 
       <xelements>7</xelements> 
    </part>
 </table>

Here's the code:

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            XmlDocument doc = new XmlDocument();
            doc.LoadXml("product.xml");
            XmlTextWriter writer = new XmlTextWriter("product.xml", System.Text.Encoding.UTF8);
            writer.WriteStartDocument(true);
            writer.Formatting = Formatting.Indented;
            writer.Indentation = 2;
            writer.WriteStartElement("Table");
            createNode(Name.Text, Cut_Area_X.Text, Cut_Area_Y.Text, Thickness.Text, Offset.Text, Number_Cuts_X.Text, Number_Cuts_Y.Text, writer);
            writer.WriteEndElement();
            writer.WriteEndDocument();
            writer.Close();
            MessageBox.Show("XML File created ! ");
        }

        private void createNode(string Name, string Length, string Width, string Thickness, string offset, string YElements, string XElements, XmlTextWriter writer)
        {
            writer.WriteStartElement("Part");
            writer.WriteStartElement("Product_Name");
            writer.WriteString(Name);
            writer.WriteEndElement();
            writer.WriteStartElement("Length");
            writer.WriteString(Length);
            writer.WriteEndElement();
            writer.WriteStartElement("Width");
            writer.WriteString(Width);
            writer.WriteEndElement();
            writer.WriteStartElement("Thickness");
            writer.WriteString(Thickness);
            writer.WriteEndElement();
            writer.WriteStartElement("Offset");
            writer.WriteString(offset);
            writer.WriteEndElement();
            writer.WriteStartElement("YElements");
            writer.WriteString(YElements);
            writer.WriteEndElement();
            writer.WriteStartElement("XElements");
            writer.WriteString(XElements);
            writer.WriteEndElement();
            writer.WriteEndElement();

        }
    }
}