How to set element value with namespace in linq?

Question

I am developing silverlight web part for sharepoint 2010. I have an xml file in my application as follows

<sst xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" count="67" uniqueCount="39">
  <si>
    <t>INVOICE</t>
  </si>
  <si>
    <t>INVOICE #</t>
  </si>
  <si>
    <t>Bill To:</t>
  </si>
  <si>
    < t>DESCRIPTION</t>
  </si>
  <si>
    <t>AMOUNT</t>
  </si>
  <si>
    <t>TOTAL</t>
  </si>
  <si>
    <t>FOR:</t>
  </si>
  <si>
    <t>Positive Behavior Support Corp</t>
  </si>
  <si>
    <t>8108 SE Coconut St.</t>
  </si>
  <si>
    <t>Hobe Sound, FL 33455</t>
  </si>
  <si>
    <t>772-349-6317 Phone  772-675-9100 Fax</t>
  </si>
  <si>
    <t>EIN 20-5268843</t>
  </si>
  <si>
    <t>Provider 693068996</t>
  </si>
  <si>
    <t>Rate</t>
  </si>
  <si>
    <t>Units</t>
  </si>
  <si>
    <t>DATE</t>
  </si>
  <si>
    <t>Michael Nolan Ph.D. BCBA</t>
  </si>
  <si>
    <t>____________________________________________</t>
  </si>
  <si>
    <t>BCBA                          Date</t>
  </si>
  <si>
    <t>CLIENT:</t>
  </si>
  <si>
    <t>Date:</t>
  </si>
  <si>
    <t>Behavior Assistant- L. Bresson</t>
  </si>
  <si>
    <t>Email:</t>
  </si>
  <si>
    <t>1 Unit = 1 hour</t>
  </si>
  <si>
    <t>TOTALS</t>
  </si>
  <si>
    <t>[email protected]</t>
  </si>
  <si>
    <t>Attn: Cecilia</t>
  </si>
  <si>
    <t>Behavior Assistant- B. Bresson</t>
  </si>
  <si>
    <t>Behaviror Ass't -N Giarratano</t>
  </si>
  <si>
    <t>Signature of Representatives Approval           Date</t>
  </si>
  <si>
    <r>
      <t xml:space="preserve">Behavior Asst- </t>
    </r>
    <r>
      <rPr>
        <sz val="9" />
        <rFont val="Arial" />
        <family val="2" />
      </rPr>
      <t>N Giarratano-</t>
    </r>
    <r>
      <rPr>
        <sz val="10" />
        <rFont val="Arial" />
        <family val="2" />
      </rPr>
      <t>08</t>
    </r>
  </si>
  <si>
    <t>Behavior Asst- B. Bresson-08</t>
  </si>
  <si>
    <t>Behavior Asst- L. Bresson-08</t>
  </si>
  <si>
    <t>&lt;@Invoice&gt;</t>
  </si>
  <si>
    <t>&lt;@For&gt;</t>
  </si>
  <si>
    <t>&lt;@Client&gt;</t>
  </si>
  <si>
    <t>&lt;@Caregiver&gt;</t>
  </si>
  <si>
    <t>&lt;@Email,@Address,@City,@State,@Zip&gt;</t>
  </si>
  <si>
    <t>&lt;@Date&gt;</t>
  </si>
</sst>

I am successfully loading this xml file. Now I am acessing all the element with name "t" from xml file as follows.

XNamespace ns = xmlDoc.Root.Name.Namespace;
            var eles = from c in xmlDoc.Descendants(ns + "si")
                       select c.Element(ns + "t");

It is also working fine. But when I use the following query it gives me error

eles.Elements(ns + "t").Where(x => x.Element(ns + "t").Value == "<@Date>").SingleOrDefault().SetElementValue(ns + "t","hi");

It gives me error as object reference is not set to instance of object. How I can replace the "<@Date> with "hi" in the existing xml. Can you please provide me any code or link through which I can resolve the above issue ?

Answer 1

Your eles variable is already returning the <t>. None of the <t> have a child that is <t>, so it makes sense that x.Element(ns + "t") doesn't return anything (thus null, thus .Value is an error). Actually, I'm a bit confused, because eles.Elements(ns + "t") should have been an empty sequence.

Also, the value in C# terms is <@Date>; the > / < only applies to xml.

Also, the query is being impacted by the one <si> that doesn't have a <t>; a better variant would be:

var eles = xmlDoc.Descendants(ns + "si").Elements(ns + "t");

(which handles 0, 1, or many <t> per <si>)

Then after that, you mean:

eles.SingleOrDefault(x => x.Value == "<@Date>").Value = "hi";