Tuesday, May 06, 2008
Recently I was playing with some LINQ to XML for a demo I was preparing and was having trouble retrieving the expected values from what was a very straightforward query.
Have a look at the XML file that looks like this (the results of programmatically calling this Amazon service).
Each
I went for the obvious:
The clue (and at the same time further "excuse") is that all my previous experiments with LINQ to XML involved using my own demo XML files that never had namespaces inside so I forgot all about them (haven't paid the tax in a while). I find quite ugly what you have to do to incorporate namespaces in a LINQ to XML query, but there seems to be no nicer alternative to the following (thanks Mike):
Have a look at the XML file that looks like this (the results of programmatically calling this Amazon service).
Each
Item element represents a book and I wanted to retrieve the Title. How would you form that query with LINQ to XML?I went for the obvious:
var res =When that did not produce the expected results I scratched my "tired" head at the time and pinged MikeT who came up with the correct way of doing this (you still have time to work it out on your own).
from ia in XElement.Parse(e.Result).DescendantsAndSelf("ItemAttributes")
select ia.Element("Title").Value;
The clue (and at the same time further "excuse") is that all my previous experiments with LINQ to XML involved using my own demo XML files that never had namespaces inside so I forgot all about them (haven't paid the tax in a while). I find quite ugly what you have to do to incorporate namespaces in a LINQ to XML query, but there seems to be no nicer alternative to the following (thanks Mike):
void SomeMethod()I still didn't like this solution for the simple demo I wanted to use it for. So, I recalled VB's superior support for XML and I converted the project to VB and used the following instead which needs no extra method and is all round more elegant:
{
var res =
from ia in XElement.Parse(e.Result).DescendantsAndSelf(n("ItemAttributes"))
select ia.Element(n("Title")).Value;
// TODO use res
}
static XName n(string name)
{
return XNamespace.Get("http://webservices.amazon.com/AWSECommerceService/2005-10-05") + name;
}
Dim res = _...and if you are wondering where the
From ia In XElement.Parse(e.Result)...<n:ItemAttributes> _
Select ia...<n:Title>.Value()
n comes from, that is at the top of the VB file:Imports <xmlns:n="http://webservices.amazon.com/AWSECommerceService/2005-10-05">...another aspect of VB's beauty and another thing I had the opportunity to mention in my demo ;-)
Labels: dot NET general, LINQ
# posted by The Moth @ 6:30:00 AM 
Comments:
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I think as with most VB features, they are great when you have a simple case(demo) but are nothing but trouble in a real complex project.
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Mr. Fischer your comment is absolutely ridiculous. Would you care to explain how this elegant feature could cause trouble in your "real complex project"?
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I think you'll find this works in C#
XElement resultXML = XElement.Load(url);
XNamespace ns = "http://schemas.microsoft.com/LiveSearch/2008/04/XML/web";
var results = resultXML.Descendants(ns + "WebResult");
_________________XElement resultXML = XElement.Load(url);
XNamespace ns = "http://schemas.microsoft.com/LiveSearch/2008/04/XML/web";
var results = resultXML.Descendants(ns + "WebResult");
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