How to exclude NULL blocks from XML using LINQ-to-XML?

问题

Consider this XML file. Note the first Tutorial has an Author child element, and the second Tutorial does not:

<?xml version="1.0" encoding="utf-8" ?>
<Tutorials>
  <Tutorial>
    <Author>The Tallest</Author>
    <Title>
      WPF Tutorial - Creating A Custom Panel Control
    </Title>
    <Date>2/18/2008</Date>
  </Tutorial>
    <Tutorial>
    <Title>
      2nd WPF Tutorial - Creating A Custom Panel Control
    </Title>
    <Date>2/18/2008</Date>
  </Tutorial>
</Tutorials>

How do I use LINQ-to-XML to load the data that is present? The code below blows up when it gets to the Tutorial section that lacks an author. I cannot figure out how to write the where statement to exclude the block that lacks an author, or how to make the code elegantly skip over the missing data. I have tried this:

where tutorial.Element("Title") != null

But the above has no effect.... Here is the problem code:

XDocument xmlDoc = XDocument.Load("C:\\xml\\2.xml");

var tutorials = from tutorial in xmlDoc.Descendants("Tutorial")
                select new
                {
                    Author = tutorial.Element("Author").Value,
                    Title = tutorial.Element("Title").Value,
                    Date = tutorial.Element("Date").Value,
                };

foreach (var tutorial in tutorials)
{
    Console.WriteLine("author: " + tutorial.Author);
    Console.ReadKey();
}

回答1:

Use the XElement to String conversion operator instead of the Value property:

var tutorials = from tutorial in xmlDoc.Root.Elements("Tutorial")
                select new
                {
                    Author = (string)tutorial.Element("Author"),
                    Title = (string)tutorial.Element("Title"),
                    Date = (DateTime)tutorial.Element("Date"),
                };

回答2:

Instead of referencing the Value property of the XElement that might be null, you can do an explicit cast to string instead, like this:

Author = (string) tutorial.Element("Author")

Check out this article for more info:

Improving LINQ Code Smell with Explicit and Implicit Conversion Operators

来源：https://stackoverflow.com/questions/8177864/how-to-exclude-null-blocks-from-xml-using-linq-to-xml

标签

linq-to-xml