如何使用C＃在xml中获取特定的子节点值

Question

I have an xml schema like below

<library>
    <book>
      <id>1</id>
      <name>abc</name>
        <read>
          <data>yes</data>
          <num>20</num>
       </read>
    </book>
    <book>
      <id>20</id>
      <name>xyz</name>
        <read>
          <data>yes</data>
          <num>32</num>
       </read>
    </book>
</library>

Now if the id is 20 i need to take the value of tag <num> under <read>

I done the code as below

 var xmlStr = File.ReadAllText("e_test.xml");
 var str = XElement.Parse(xmlStr);
 var result = str.Elements("book").Where(x => x.Element("id").Value.Equals("20")).ToList();

this give the whole <book> tag with id 20 . From this how can I extract only the value of tag <num> .

ie is i need to get the value 32 in to a variable

Answer 1

Before you try to extract the num value, you need to fix your Where clause - at the moment you're comparing a string with an integer. The simplest fix - if you know that your XML will always have an id element which has a textual value which is an integer - is to cast the element to int .

Next, I'd use SingleOrDefault to make sure there's at most one such element, assuming that's what your XML document should have.

Then you just need to use Element twice to navigate down via read and then num , and cast the result to int again:

// Or use XDocument doc = ...; XElement book = doc.Root.Elements("book")...
XElement root = XElement.Load("e_test.xml")
XElement book = root.Elements("book")
                    .Where(x => (int) x.Element("id") == 20)
                    .SingleOrDefault();
if (book == null)
{
    // No book with that ID
}
int num = (int) book.Element("read").Element("num");

Answer 2

If you're not dead set on using Linq, how about this XPath? XPath is probably more widely understood, and is really simple. The XPath to find your node would be:

/library/book[id=20]/read/num

Which you could use in C# thus:

var doc = new XmlDocument();
doc.LoadXml(myString);
var id = 20;
var myPath = "/library/book[id=" + id + "]/read/num";

var myNode = doc.SelectSingleNode(myPath);

Then you can do whatever you like with myNode to get its value etc..

Helpful reference:

http://www.w3schools.com/xsl/xpath_syntax.asp