Working with Xml DOM

By: Saurabh Nandu - Sunday, September 23, 2001 Add Comment

<div align="center"> <table width="75%" class="outline"> <tr> <td width="50%" class="outline">Download</td> <td width="50%" class="outline">SDK</td> </tr> <tr> <td width="50%" class="outline"> <a class="wbox" href="../../file/xmldom.zip">xmldom.zip</a> (5kb)</td> <td width="50%" class="outline">Beta2</td> </tr> </table> </div> Introduction Xml - The standard for representing data over the internet is indeed very powerful and has a lot of importance in today's connected world, but very few platforms have been able to fully support Xml and its various specifications. On the .NET Platform, Microsoft has clearly displayed its interest in supporting Xml by providing an extensive API that fully supports the latest Xml standards. Xml DOM <a class="wbox" target="_blank" href="http://www.W3C.org">W3C</a> has specified the Xml DOM (Document Object Model) as a standard programming interface for handling Xml Documents. The Xml DOM treats a Xml Document as a tree of nodes. Every individual data item is treated as a Node, any text or sub data items are treated as sub-nodes (child nodes).  Table 1: Possible Node Types according to W3C and corresponding .NET Class  <table border="0" width="100%" class="outline"> <tr> <td width="50%" class="outline">Xml Node Type</td> <td width="50%" class="outline">.NET Framework Class</td> </tr> <tr> <td width="50%" class="outline">Element</td> <td width="50%" class="outline">XmlElement</td> </tr> <tr> <td width="50%" class="outline">Attribute</td> <td width="50%" class="outline">XmlAttribute</td> </tr> <tr> <td width="50%" class="outline">Text</td> <td width="50%" class="outline">XmlText</td> </tr> <tr> <td width="50%" class="outline">CDATA Section</td> <td width="50%" class="outline">XmlCDataSection</td> </tr> <tr> <td width="50%" class="outline">Entity Reference</td> <td width="50%" class="outline">XmlEntityReference</td> </tr> <tr> <td width="50%" class="outline">Entity</td> <td width="50%" class="outline">XmlEntity</td> </tr> <tr> <td width="50%" class="outline">Processing Instruction</td> <td width="50%" class="outline">XmlProcessingInstruction</td> </tr> <tr> <td width="50%" class="outline">Comment</td> <td width="50%" class="outline">XmlComment</td> </tr> <tr> <td width="50%" class="outline">Document</td> <td width="50%" class="outline">XmlDocument</td> </tr> <tr> <td width="50%" class="outline">Document Type</td> <td width="50%" class="outline">XmlDocumentType</td> </tr> <tr> <td width="50%" class="outline">Document Fragment</td> <td width="50%" class="outline">XmlDocumentFragement</td> </tr> <tr> <td width="50%" class="outline">Notation</td> <td width="50%" class="outline">XmlNotation</td> </tr> </table> The .NET Framework places these classes under the 'System.Xml' namespace, 'System.dll' assembly. The .NET SDK Beta2 provides full support W3C Xml DOM level 1 (core) 'http://www.w3c.org/TR/REC-DOM-Level-1/' as well as for W3C Xml DOM level 2 'http://www.w3c.org/TR/DOM-Level-2/'. Code: In this article we will learn to manipulate data within a Xml document using the Xml DOM specification. Of course please remember that the focus of this article is to help you learn C# Programming and not Xml DOM! 1) Contacts.Xml : Xml Document<table border="0" width="100%" class="code"> <tr> <td width="100%"> <pre><?xml version="1.0"?> <Contacts> <Contact ContactID="1021"> <FirstName>Nanu</FirstName> <LastName>Jogi</LastName> </Contact> <Contact ContactID="3267"> <FirstName>Saurabh</FirstName> <LastName>Nandu</LastName> </Contact> <Contact ContactID="1002"> <FirstName>Pritesh</FirstName> <LastName>Nandu</LastName> </Contact> </Contacts></pre> </td> </tr> </table>  2) Contacts.cs - The Example Class <table border="0" width="100%" class="code"> <tr> <td width="100%"> <pre>using System; using System.Xml; using System.IO; public class Contacts { private XmlDocument contactDoc; //Path to the data file private string docPath="contacts.xml"; public static void Main() { Contacts myContacts = new Contacts(); } public Contacts() { //Open a FileStream on the Xml file FileStream docIn = new FileStream(docPath,FileMode.Open,FileAccess.Read,FileShare.ReadWrite); contactDoc = new XmlDocument(); //Load the Xml Document contactDoc.Load(docIn); //Display the contacts DisplayContacts(); //Add a Contact AddContact(); //Display the contacts DisplayContacts(); //Edit a Contact EditContact(); //Display the contacts DisplayContacts(); //Delete a Contact DeleteContact(); //Display the contacts DisplayContacts(); }</pre> </td> </tr> </table> Above is the definition of the class Contacts, this is a normal Console Application. Within the class I define two private variables, one is of the type XmlDocument and other is a string holding the path to the Xml Document. Then in the constructor of the class I make calls to various methods which will manipulate the Xml data using the Xml DOM. <table width="100%" class="code"> <tr> <td > <pre> private void DisplayContacts() { //Get a list of all XmlNodes with the TAG Contact XmlNodeList contactsList = contactDoc.GetElementsByTagName("Contact"); Console.WriteLine("Displaying the Contacts... \r\n"); //Iterate through the Nodes for(int i=0;i<contactsList.Count;i++) { //Get the AttribuitesCollection for the Contact element XmlAttributeCollection attrColl = contactsList[i].Attributes; //Display the Attribute Name and Value Console.Write("Contact "+attrColl[0].Name); Console.WriteLine(":\t"+attrColl[0].Value); //Display the FirstChild element's Name and Text Console.Write("Contact "+contactsList[i].FirstChild.Name); Console.WriteLine(":\t"+contactsList[i].FirstChild.InnerText); //Display the LastChild element's Name and Text Console.Write("Contact "+contactsList[i].LastChild.Name); Console.WriteLine(":\t"+contactsList[i].LastChild.InnerText); Console.WriteLine(); } Console.WriteLine("Contacts List Over... \r\n\r\n"); }</pre> </td> </tr> </table> The above listing shows the implementation of the DisplayContacts method, this method iterates over all the XmlNode's in the document and displays their content. My implementation is very tightly coupled with the Xml data that I am going to work with, incase you need a generic method to iterate over the XmlNode's refer to the Quick Start tutorials. <img border="0" src="../../img/xmldomcon1.gif" width="332" height="263"> Figure 1: Display Contacts   <table width="100%" class="code"> <tr> <td > <pre> private void AddContact() { Console.WriteLine("Adding a New Contact\r\n"); //Create a new XmlElement XmlElement newContact = contactDoc.CreateElement("Contact"); //Create a new XmlAttribute XmlAttribute idAttribute = contactDoc.CreateAttribute("ContactID"); idAttribute.Value = "2345"; //Set the Attribute on the XmlElement newContact.SetAttributeNode(idAttribute); //Create a new XmlElement XmlElement firstElement = contactDoc.CreateElement("FirstName"); firstElement.InnerText="Nitin"; //Add the Append the element as an child newContact.AppendChild(firstElement); XmlElement lastElement = contactDoc.CreateElement("LastName"); lastElement.InnerText="Batta"; newContact.AppendChild(lastElement); //Insert the newly created XmlElement into the XmlDocument //before the LastChild contactDoc.DocumentElement.InsertBefore(newContact, contactDoc.DocumentElement.LastChild); //Create a FileStream and Save the Document FileStream docOut = new FileStream(docPath,FileMode.Truncate,FileAccess.Write,FileShare.ReadWrite); contactDoc.Save(docOut); }</pre> </td> </tr> </table> The above AddContact method is used to append a new contact to the document. I have used the XmlDocment class's methods to create new XmlAttribute's and XmlElement's. Finally the XmlNode is inserted in the XmlDocument before the LastChild and the document is saved. <img border="0" src="../../img/xmldomcon2.gif" width="332" height="323"> Figure 2: Add a new Contact <table width="100%" class="code"> <tr> <td > <pre> private void EditContact() { Console.WriteLine("Editing a Contact\r\n"); //Use an XPath query to find a XmlNode XmlNode editContact = contactDoc.SelectSingleNode("descendant::Contact[FirstName='Nitin']"); //Check if the XmlNode has Child Nodes if(editContact.HasChildNodes) { //Change the FirstChild Elemets InnerText editContact.FirstChild.InnerText="Sanddy"; } //Save the Document FileStream docOut = new FileStream(docPath,FileMode.Truncate,FileAccess.Write,FileShare.ReadWrite); contactDoc.Save(docOut); }</pre> </td> </tr> </table> The EditContact method shown above executes an XPath query on the Xml Document and selects the XmlNode with the element Contact which has an ChildElement FirstName equal to Nitin. Once we have the XmlNode, we change the text of the FirstName element and save the file. <img border="0" src="../../img/xmldomcon3.gif" width="332" height="323"> Figure 3: Edit a Contact <table width="100%" class="code"> <tr> <td > <pre> private void DeleteContact() { Console.WriteLine("Deleting a Contact\r\n"); //Use an XPath query to find a XmlNode XmlNode deleteContact = contactDoc.SelectSingleNode("descendant::Contact[FirstName='Sanddy']"); //Remove the XmlNode from the Document contactDoc.DocumentElement.RemoveChild(deleteContact); //Save the Document FileStream docOut = new FileStream(docPath,FileMode.Truncate,FileAccess.Write,FileShare.ReadWrite); contactDoc.Save(docOut); }</pre> </td> </tr> </table> Just like the EditContact method, in the DeleteContact method too we use an XPath query to select the XmlNode having the FirstName child element's value equal to Sanddy. Once the Node is found we remove it from the document and save the document. Conclusion In this article we saw how to manipulate Xml data using the Xml DOM classes from the .NET Framework. You can modify these methods and dig a bit more into the reference documentation to get more information!

Working with Xml DOM

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