This post is about understanding Descendants and avoiding misconception with this method.
Recently, I read one question on StackOverFlow about reading XML using LINQ To XML to get node values. In that, a developer made use of Descendants Method to get the child node values.

Let's see the actual problem here. Following is the XML to read and the developer wrote code to read out the value of orderid node.

<ordersreport date="2012-08-01">
<returns>
      <amount>
        <orderid>2</orderid>
        <orderid>3</orderid>
        <orderid>21</orderid>
        <orderid>23</orderid>
      </amount>
    </returns>
</ordersreport>

So code is written like this:

var amount = documentRoot.Descendants("Amount")
           .Select(y => new
           {
              OrderId = (int)y.Element("OrderId")
           });
           foreach (var r in amount)
           {
              Console.WriteLine(r.OrderId);
           }

Output of the above code is: 2.

That is only first orderid element value which is the child of Amount. So, the misconception here by developer of the code is Descendants("Amount") returns child element of the Amount tag, i.e., all orderId element.

Now to Understand Descendants function in a better way, I visited the MSDN link which says something like this
XContainer.Descendants Method (XName) - Returns a filtered collection of the descendant elements for this document or element, in document order. Only elements that have a matching XName are included in the collection. So as per the definition on MSDN problem with code...

var amount = doc.Descendants("Amount")
  .Select(y => new
  {
   OrderId = (int)y.Element("OrderId")
   });

...will give you Element Amount and when you write y.Element("OrderId") will return you fist element of its child.

Descendants - doesn't mean than it returns the child element of element name rather than method. Look for descendants of element or if name of element specified as parameter than matching descendants.
Finally, I got the following solution to get it to work properly.

XElement documentRoot  = 
     XElement.Parse (@"<ordersreport date="2012-08-01">
                             <returns>
                              <amount>
                                  <orderid>2</orderid>             
                                  <orderid>3</orderid>
                                  <orderid>21</orderid>
                                  <orderid>23</orderid>
                               </amount>
                             </returns>
                        </ordersreport>");

Solution 1

var orderids = from order in
                  documentRoot.Descendants("Amount").Descendants()
                  select new
                  {
                     OrderId = order.Value
                  };

As per the information on MSDN, documentRoot.Descendants("Amount").Descendants() gives a list of orderId elements.

Solution 2

var orderids = from order in
                    documentRoot.Descendants("OrderId")
                    select new
                    {
                       OrderId = order.Value
                    };

Or the second solution is just a bit easy than this. Just make use of documentRoot.Descendants("OrderId") that will give all orderid element.

Conclusion

This post is just for avoiding the misconception related to Descendants and understanding it properly.

Leave your comments if you like it.

CodeProject