maximum DateTime in XML

Question

I am trying to find the maximum DateTime value in my XML.

Here is a sample of the XML:

<?xml version="1.0" encoding="utf-16"?>
<?xml-stylesheet type='text/xsl' href='http://127.0.0.123/sitemaps/xmltemplate/main-sitemap.xsl'?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
  <url>
    <loc>http://127.0.0.123/?????</loc>
    <lastmod>2018-05-13</lastmod>
    <changefreq>daily</changefreq>
    <priority>0.1</priority>
  </url>
  <url>
    <loc>http://127.0.0.123/?????-????</loc>
    <lastmod>2018-05-26</lastmod>
    <changefreq>daily</changefreq>
    <priority>0.1</priority>
  </url>
</urlset>

And here's the code I'm trying to use:

XDocument xdoc = XDocument.Load(FullAddressXML);
var maxId = xdoc.Elements("url").Select(x => new {                
        MaxDateTime = x.Descendants("lastmod").Max(y=>(DateTime)y)
    });

When I run this, maxId is empty.

Please could you give more details than "it dosent work"? Does it fail to compile? Does it compile but throw an exception? (And if so, what exception?) Does it not throw an exception, but not give you the answer you expect? — Jon Skeet, Jun 02 '18 at 11:21
So please edit that detail into the question. A question which only states "It doesn't work" is never a good question. — Jon Skeet, Jun 02 '18 at 11:25

score 4 · Accepted Answer · answered Jun 02 '18 at 11:28

There are three problems here:

You're calling xdoc.Elements("url") which will never return any elements, because there are no url elements as the direct descendant of the document; you'd want xdoc.Root.Elements to find the url elements within the root element
You're providing the local name of the elements, but due to namespace defaulting, they're actually in a namespace of "http://www.sitemaps.org/schemas/sitemap/0.9" which you aren't specifying, so it won't find any elements
You're finding a sequence of maximum DateTime values, one per url element, which almost certainly isn't what you want to do - you presumably want the maximum across all URLs.

Additionally, it's not clear why you're creating a new anonymous type with a single property - that's usually not useful.

Here's an example which works for your sample data:

using System;
using System.Linq;
using System.Xml.Linq;

public class Test
{
    static void Main()
    {
        var doc = XDocument.Load("test.xml");
        XNamespace ns = "http://www.sitemaps.org/schemas/sitemap/0.9";
        var max = doc.Root
            .Elements(ns + "url")
            .Max(url => (DateTime) url.Element(ns + "lastmod"));
        Console.WriteLine(max);
    }
}

Alternatively, if there will never be any other lastmod elements, you could just use Descendants on the document itself:

var max = doc.Descendants(ns + "lastmod").Max(x => (DateTime) x);

maximum DateTime in XML

1 Answers1