XElement.Element returning null for newly created element

Question

I am using XElement to create an XMLDocument which is used in a hierarchical WPF treeview. If I create a new element with :

    x_element = new XElement("node",
    new XElement("tree_id", strData[0]),
    new XElement("sys_id", dpl.DepSysId),
    new XElement("part_id", strData[8]),
    new XElement("make", strData[6]),
    new XElement("model", strData[5]),
    new XElement("level", strData[2]));

I then need to add attributes to "node" so I tried:

   XElement temp_el = x_element.Element("node"); // This is returning null
   temp_el.SetAttributeValue("title", strData[7] + " " + strData[6] + " " + strData[5]);
   temp_el.SetAttributeValue("canEdit", "False");
   temp_el.SetAttributeValue("status", nStatus.ToString());
   temp_el.SetAttributeValue("qty", strData[13]);
   temp_el.SetAttributeValue("part", strData[8]);

In the above code temp_el is null, but I can see in the debugger that x_element contains the following :

<node>
  <tree_id>82</tree_id>
  <sys_id>82</sys_id>
  <part_id>169</part_id>
  <make>ST Panel</make>
  <model>Logical Pure 16 tube Collector</model>
  <level>0</level>
</node>

To work around this I have used the following:

   foreach (XElement temp_el in x_element.DescendantsAndSelf())
   {
       if (temp_el.Name == "node")
       {
           temp_el.SetAttributeValue("title", strData[7] + " " + strData[6] + " " + strData[5]);
           temp_el.SetAttributeValue("canEdit", "False");
           temp_el.SetAttributeValue("status", nStatus.ToString());
           temp_el.SetAttributeValue("qty", strData[13]);
           temp_el.SetAttributeValue("part", strData[8]);
           break;
       }
   }

Whilst the above works I am just curious as to why I am getting null returned. Is my workaround the best way of doing this?

Regards.

Answer 1

You defined your XElement like this:

x_element = new XElement("node", /* child nodes */);

Where "node" is the name of the XElement you are creating, and the following parameters are its children.

By using x_element.Node("node"), you are trying to get the child node named "node", and there isn't such a child node.
x_element itself is the node named "node".
DescendantsAndSelf worked because it includes x_element (hence "AndSelf"), but you don't need this either because you already have the node.

So you can change your second code snippet to this:

x_element.SetAttributeValue("title", strData[7] + " " + strData[6] + " " + strData[5]);
x_element.SetAttributeValue("canEdit", "False");
// etc.

(BTW, you can also add the Attributes in the constructor)

Answer 2

Because with your first temp_el,

XElement temp_el = x_element.Element("node");

You used to get nodes which is not treated to be an Element of x_element.

It was treated as its root. However, with the second one,

x_element.DescendantsAndSelf()`

You used this XElement Method which treat node itself as an element.

XContainer.Elements Method - Returns a collection of the child elements of this element or document, in document order.

XElement.DescendantsAndSelf Method - Returns a collection of elements that contain this element, and all descendant elements of this element, in document order.

Answer 3

To solve the issue I used Descendants(). Here is my code snippet

public void UpdateEnquiry([FromBody]XElement UpdatePurchaseOrder)
        {
            var obj = XElement.Parse(UpdatePurchaseOrder.ToString());
            var ii = (from v in obj.Descendants() select new { v.Value }).ToList() ;
         }