C# load xml data with attributes to datagridview; update data and save back to the xml

Hi guys,

i currently have this XML as data

<DEALS><DEAL ID="22" ISBN="0-7888-1623-3" Screenplay="Mary Kaplan" Title ="Mr Gentleman" Director = "Jonathan Jones"><ALLOCATION DEMANDE="5000" CODE="72" PRICE="25.00">2500</ALLOCATION><ALLOCATION DEMANDE="7000" CODE="75" PRICE="35.00">4000</ALLOCATION></DEAL><DEAL ID="23" ISBN="1-7988-1623-3" Screenplay="Joe Doe" Title ="Nothing Much" Director = "Listentome"><ALLOCATION DEMANDE="3300" CODE="72"  PRICE="15.00">2500</ALLOCATION></DEAL></DEALS>

I load the data with the code below:

i use xDocument to load the DealData.xml and then put it in ToString.

//outside of the form
public static class XElementExtensions
    {
        public static DataTable ToDataTable(this XElement element)
        {
            DataSet ds = new DataSet();
            string rawXml = element.ToString();
            ds.ReadXml(new StringReader(rawXml));
            return ds.Tables[0];
        }


        public static DataTable ToDataTable(this IEnumerable<XElement> elements)
        {
            return ToDataTable(new XElement("Root", elements));
        }
    }



//in the form

        private void button2_Click(object sender, EventArgs e)
        {
            var xDocument = XDocument.Load("DealData.xml");
            string txtxml = xDocument.ToString();

            StringReader reader = new StringReader(txtxml);
            XDocument doc1 = XDocument.Load(reader);
            var res = doc1.Descendants("DEAL").ToList().Where(x => x.Attribute("ID").Value == "22").Descendants("ALLOCATION");

            dataGridView1.DataSource = res.ToDataTable();
        }

Now my question is:

I would like to update the data from the DataGridview with the Attribute("ID").Value == "22" and save the data back to the XML.

For example, after I load my data on the datagridview, we only pickup anything that is in the node

<DEAL ID="22" ISBN="0-7888-1623-3" Screenplay="Mary Kaplan" Title ="Mr Gentleman" Director = "Jonathan Jones"><ALLOCATION DEMANDE="5000" CODE="72" PRICE="25.00">2500</ALLOCATION><ALLOCATION DEMANDE="7000" CODE="75" PRICE="35.00">4000</ALLOCATION></DEAL>

I updated the datagridview below with DEMANDE = 9000 CODE = 66 PRICE = 24.77 AND ALLOCATION = 1200

I want be able to extract the data back in the xml as a child of the DEAL ID = "22"

So that the XML file looks like this 

<DEALS><DEAL ID="22" ISBN="0-7888-1623-3" Screenplay="Mary Kaplan" Title ="Mr Gentleman" Director = "Jonathan Jones"><ALLOCATION DEMANDE="5000" CODE="72" PRICE="25.00">2500</ALLOCATION><ALLOCATION DEMANDE="7000" CODE="75" PRICE="35.00">4000</ALLOCATION><ALLOCATION DEMANDE="9000" CODE="66" PRICE="24.77">1200</ALLOCATION>   <-! this is the new line !-></DEAL><DEAL ID="23" ISBN="1-7988-1623-3" Screenplay="Joe Doe" Title ="Nothing Much" Director = "Listentome"><ALLOCATION DEMANDE="3300" CODE="72"  PRICE="15.00">2500</ALLOCATION></DEAL></DEALS>

Is there a way to achieve that?
I have been searching and reading in the books but i cannot find a solution for this.

Thank you

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