Question

Here’s the problem I have a xml file that I am trying to append data to. I am using LINQ to XML and the code I am using is as follows:

    public void AppendSalesXMLData(Company company)
    {
        string FileName = "TestSales";
        string OrgID = company.OrgID.ToString();
        string SaleID = company.OrgSales[company.OrgSales.Count - 1].SaleID.ToString();

        if (!File.Exists(String.Format(@"C:\Data-Source\trunk\Applications\VintageSiteInspector\XML\{0}.xml", FileName)))
        {
            CreateXMLFile(FileName);
        }
        XDocument thisDoc = XDocument.Load(String.Format(@"C:\Data-Source\trunk\Applications\VintageSiteInspector\XML\{0}.xml", FileName));

        <!------- The following line throws an exception every time. ----->
        thisDoc.Element(FileName).Add(new XElement("Sale")); 


        thisDoc.Save(String.Format(@"C:\Data-Source\trunk\Applications\VintageSiteInspector\XML\{0}.xml", FileName));
    }

The XML file that I am opening is

<?xml version="1.0" encoding="utf-8"?>
<root>
 <TestSales></TestSales>
</root>

I just don’t see why I am getting a null reference exception.

Answer 1

Element refers to direct child (which in your case would be root, not TestSale). Try Descendants instead:

thisDoc.Descendants(FileName).First().Add(new XElement("Sale"));

Alternatively, when you know XML tree you can also simply walk it like this:

thisDoc.Element("root").Element(FileName).Add(new XElement("Sale"));