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Adding an Attribute to an XML Element

Posted on 2004-10-04
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Last Modified: 2013-11-19
I have an XML document, and I would like to add an attribute to a particular element. For example, in the following XML (not fully shown), there is an element called s:any:

...
<s:element name="TypedDataSet">
  <s:complexType>
    <s:sequence>
      <s:any />
    </s:sequence>
  </s:complexType>
</s:element>
...

I want to add an attribute namespace="http://www.tempuri.org/TypedDataSet.xsd" to all elements with s:any name. In the above example, the result will be like:

...
<s:element name="TypedDataSet">
  <s:complexType>
    <s:sequence>
      <s:any namespace="http://www.tempuri.org/TypedDataSet.xsd"/>
    </s:sequence>
  </s:complexType>
</s:element>
...

I would appreciate a full example showing how to read the XML document, adding in the attribute, and saving the document.

Thanks in advance.
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Question by:yongsing
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Expert Comment

by:KeithWatson
Comment Utility
OK, this should do the trick; it shows reading from a string literal and from disk.

You need to include:

using System.Xml;
using System.IO;

// I had to remove the namespace prefix; you've only supplied part of the XML document (it won't parse without it)
string s = "<element name='TypedDataSet'><complexType><sequence><any /></sequence></complexType></element>";

XmlDocument document = new XmlDocument();
document.LoadXml(s);

// Alternative, to read from a file on disk rather from the string above
// document.Load(new XmlTextReader("file://c:\\test.xml"));

// This may have to change to "//s:any" in your document
XmlElement element = (XmlElement) document.SelectSingleNode("//any");

element.SetAttribute("namespace", "http://www.tempuri.org/TypedDataSet.xsd");

// Write the output to a file on disk

StreamWriter writer = new StreamWriter("c:\\testoutput.xml");
writer.Write(document.InnerXml);
writer.Close();


Hope that helps.
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Expert Comment

by:KeithWatson
Comment Utility
Incidentally, I was perhaps a little terse on the XPath statement; you may be better with a precise path such as:

XmlElement element = (XmlElement) document.SelectSingleNode("/element/complexType/sequence/any");

(Which as I stated you may need to qualify with the "s" namespace prefix")

Keith.
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by:yongsing
Comment Utility
Thanks, it works.

If the "any" element is qualified with some other unknown namespace, can I still add the attribute? For example, it could be qualified with "xxx" or even not qualified with any namespace. In other words, I want to add the attribute to all elements with the name "any" regardless of what namespace it is qualified with.
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Expert Comment

by:KeithWatson
Comment Utility
If you can get a reference to the node without knowing the namespace (which is perfectly possible) then yes. The implementation of XPath I've used most does insist that you qualify XPath expressions with namespaces, which makes sense, since they are effectively differently named nodes, in the same way that two classes in C# with the same name but living in different namespaces are distinct entities in their own right.

You could write a similar program however not using XPath that recursed down all of the nodes in the tree looking for nodes with the name "Any" and performing exactly the same operation as above on each of these elements.
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Author Comment

by:yongsing
Comment Utility
Hi, sorry for not getting back earlier. For your suggestion of recursing  down all of the nodes in the tree looking for nodes with the name "any", can you provide an example? Thanks!
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Accepted Solution

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KeithWatson earned 300 total points
Comment Utility
Here's some sample code... Note that the second method calls itself (i.e. it's recursive).


private void testMethod() {

      /* Make a test string */
      string testXmlString = "<Test><Node2><Keith></Keith></Node2></Test>";

      /* Load this into an XmlDocument object */
      XmlDocument document = new XmlDocument();
      document.LoadXml(testXmlString);

      /* Get a handle to the root node of the document */
      XmlElement rootNode = (XmlElement) document.ChildNodes.Item(0);

      /* Call the recursive function looking to add the namespace attribute to nodes named 'Keith' */
      addAttributeToNodeWithName(rootNode, "Keith");

      /* Write the document as it is now to the console */
      Console.WriteLine(document.OuterXml);

}



private void addAttributeToNodeWithName(XmlElement node, string withName) {

      /* If this node matches the pattern, add the namespace attribute */

      if (node.Name.Equals(withName)) {
            node.SetAttribute("namespace", "Keith");
      }

      /* Recurse on any children and do the same thing with them */
            
      foreach (XmlElement childNode in node.ChildNodes) {
            addAttributeToNodeWithName(childNode, withName);
      }

}


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Author Comment

by:yongsing
Comment Utility
Hi Keith, thanks.

If I add the following to the XML, it won't work:

string testXmlString = "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                                 "<Test><Node2><Keith></Keith></Node2></Test>";

There will be an exception on this line:
XmlElement rootNode = (XmlElement) document.ChildNodes.Item(0);

It can be fixed by changing the index from 0 to 1:
XmlElement rootNode = (XmlElement) document.ChildNodes.Item(1);

How can I know that there is a <?xml ... ?> in front?
0
 
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Author Comment

by:yongsing
Comment Utility
I just found out that you need to check whether the type is XmlElement:

for (int i = 0; i < document.ChildNodes.Count; i++)
{
   if (document.ChildNodes.Item(i) is XmlElement)
   {
      XmlElement xmlElement = (XmlElement)document.ChildNodes.Item(i);
      addAttributeToNodeWithName(xmlElement, "any");
   }
}

I'll get back to you again... :)
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Author Comment

by:yongsing
Comment Utility
Thanks Keith, I finally got what I want!
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