LINQ to XML Newbie Question

is there a better way to do this kind of thing:

var filter = new CashFilters();
var element = XElement.Parse(request.OuterXml);

var productId = element.Elements("ProductId").Select(el => el);

if (productId.Count() == 1)
    filter.ProductId = Convert.ToInt32(productId.Single().Value);

From stackoverflow

• Well, the Select(el => el) isn't doing you any good to start with.

  I suggest you use SingleOrDefault:

  var productId = element.Elements("ProductId").SingleOrDefault();
  if (productId != null)
      filter.ProductId = Convert.ToInt32(productId.Value);
  

  Note that that handles the case where there are no ProductId elements, but will throw an exception if there's more than one. If that's actually a valid case, then your current code (without the redundant Select call) is reasonable.

  EDIT: You could get away from this with:

  var productId = element.Elements("ProductId")
                         .Select(elt => elt.Value)
                         .SingleOrDefault();
  filter.ProductId = Convert.ToInt32(productId ?? filter.ProductId.ToString());
  

  But that's pretty ghastly ;)

  Basically you've got a condition - you only want to set the ProductId if it's specified. An "if" statement is the generally accepted way of conditionally executing code :)

  There are alternatives:

  filter.ProductId = productId == null 
                     ? filter.ProductId 
                     : int.Parse(productId);
  

  If you don't mind filter.ProductId being set to 0 if there's no ID specified, then you can just use:

  filter.ProductId = Convert.ToInt32(element.Elements("ProductId")
                                            .Select(elt => elt.Value)
                                            .SingleOrDefault());
  

  (due to the way that Convert.ToInt32 returns 0 when passed a null argument.)

  AWC : so there's no way to get ride of the null check? great book by the way :)

• Do you REALLY need to do this in Linq to Xml? The Xml DOM approach seems much more reasonable to me.

  Have you considered the pure Xml approach?

      XmlDocument doc = new XmlDocument();
      doc.LoadXml(request.OuterXml);
  
      var node = doc.SelectSingleNode("//ProductId[1]");
      if (node != null)
          filter.ProductId = Convert.ToInt32(node.InnerText);
  

  Jon Skeet : Personally I prefer the LINQ to XML approach - less scary (uncompiled) string stuff to go wrong. Simply using Elements("ProductId").SingleOrDefault() does the same as the XPath expression, but with less to know IMO.