Summary How to auto-increment an unique ID in XML with XmlTextReader?

If you have worked with databases then you know that you can assign some fields to use auto increment values. They can be very useful, if you want to edit an item. All you will need is the ID of the item. In an XML file you can also create such a auto increment element. However you will need to increment manually with a self-defined function. In this example you will see how you can create such a function.

One important thing that you should know is that, when ever you increment the ID, its better to lock the file prior doing that. The reason for locking the XML file is that if somebody else uses the function you will have duplicated ID's.

I am using the following XML for the example. As you can see each person contains an ID. The highest person ID is 15 so the function should return 16 as the next ID.

Output:

16

Additional information

<%@ import namespace="System.Xml" %> <%@ import namespace="System.IO" %> <%@ page language="C#" debug="true"%> <script runat="server"> void page_load(object sender, System.EventArgs e){ // Return the next ID Response.Write(GetNextNodeID().ToString()); // Create new elements with the ID here // ... } private int GetNextNodeID() { // Read the xml file and lock it, so that somebody // else is not able to use it. FileStream file; file = new FileStream(Server.MapPath("XmlTextReaderWithUniqueID.xml"), FileMode.Open, FileAccess.ReadWrite, FileShare.None); // Pass the filestream to the XmlTextReader XmlTextReader reader = new XmlTextReader(file); // The unique id starts with 0 int nMaxID = 0; // Iterate through all nodes while (reader.Read()) { // Check whether the element is 'person' if (reader.IsStartElement() && reader.Name == "person") { // Convert the id to an integer int nID = Int32.Parse(reader.GetAttribute("id")); // This if gets the largest person id if(nMaxID < nID) nMaxID = nID; } } // Close the file. Now this file is again open for all. file.Close(); // Increment the ID here! nMaxID++; return nMaxID; } </script>

Further additional information

<?xml version="1.0" encoding="ISO-8859-1"?> <employee> <person id="1"> <firstname>Bob</firstname> <lastname>Jones</lastname> <active>true</active> </person> <person id="5"> <firstname>Bob</firstname> <lastname>Jones</lastname> <active>true</active> </person> <person id="9"> <firstname>Bob</firstname> <lastname>Jones</lastname> <active>true</active> </person> <person id="15"> <firstname>Mike</firstname> <lastname>Anthony</lastname> <active>false</active> </person> </employee>

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