XML Handling Part 3 - Editing an XML

Ημερομηνία: 18/08/2013

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In the previous articles we had quite a lot of talk about XMLs. We learned what XML is, how to read and create XML files. We also talked about XMLDocument. In this article, the last one of the XML series, we are going to use XMLDocument to update existing XML files.

Edit XML values

We are going to use an XML, similar to the one we have been using all along.

<?xml version="1.0" encoding="utf-8"?>

<Sms>

<Body>Good morning!</Body>

</Sms>

<Sms>

</Sms>

<Sms>

<Body>Bon Voyage!</Body>

</Sms>

</SmsDataSet>

The way to edit is quite simple.

Create an XMLDocument object.
Load the XML we want to update
Select the nodes we want to update.
Update the nodes
Save the XMLDocument object.

Here's a simple example to see how it works. This code will select the SMS node having Id = 2, and update its Body value to "Updated Value". We use ChildNodes[2], because we know that Body element is the third element within an Sms node. We have to use integer indexing as XmlNodeList does not allow selecting using string values.

bool UpdateXMLValues()

{

bool success = true;

try

{

string xmlFile = Server.MapPath("XMLFile.xml");

// Load the XML file into an XmlDocument.

XmlDocument doc = new XmlDocument();

doc.Load(xmlFile);

//Get a list of nodes based on their tag name, where Id = 2, using a filter

XmlNodeList nodes = doc.SelectNodes("/SmsDataSet/Sms[Id=2]");

foreach (XmlNode node in nodes)

node.ChildNodes[2].InnerText = "Updated Value";

//We could use the following line if we wanted to update attribute values

// node.SetAttribute("attr", "attribute");

doc.Save(xmlFile);

}

catch(Exception ex)

{

success = false;

}

return success;

}

The result will be

<?xml version="1.0" encoding="utf-8"?>

<Sms>

<Body>Good morning!</Body>

</Sms>

<Sms>

</Sms>

<Sms>

<Body>Updated Value</Body>

</Sms>

</SmsDataSet>

Insert XML values

We are now going to insert a new node within our XML. It's not much different than updating existing nodes. Here's what we need.

Create an XMLDocument object.
Load the XML we want to update
Select the parent node we will place the new node.
Create the node and insert info
Append the new node to the parent node
Save the XMLDocument object.

In the example we are going to insert a new Sms node. First, we select the SmsDataSet node. This will be our parent node. Then, we create a new Sms node using the CreateElement method. We go on, creating the inner nodes (Id, Numbers etc). We append all new nodes to the Sms node using the AppendChild method. Finally we append the Sms node to the parent SmsDataSet node.

Since there is an Id node that should get an auto increment value, we compute the number of Sms nodes and place its number in the Id value of the new node.

bool InsertXMLValues()

{

bool success = true;

try

{

string xmlFile = Server.MapPath("XMLFile.xml");

// Load the XML file into an XmlDocument.

XmlDocument doc = new XmlDocument();

doc.Load(xmlFile);

//Get the number of nodes to compute the new Id

int numberOfSms = doc.SelectNodes("/SmsDataSet/Sms").Count;

//Get the parent node

XmlNode node = doc.SelectSingleNode("/SmsDataSet");

//Create the new element

XmlNode newNode = doc.CreateElement("Sms");

//Create and fill inner elements

XmlNode newNodeId = doc.CreateElement("Id");

newNodeId.InnerText = (numberOfSms).ToString();

XmlNode newNodeNumbers = doc.CreateElement("Numbers");

newNodeNumbers.InnerText = "+31028237923";

XmlNode newNodeBody = doc.CreateElement("Body");

newNodeBody.InnerText = "New Node! Yeah!";

//Include more elements

// ........

//Append inner elements to the new element

newNode.AppendChild(newNodeId);

newNode.AppendChild(newNodeNumbers);

newNode.AppendChild(newNodeBody);

//Append more elements

// ........

//Append the new element to the parent

node.AppendChild(newNode);

//Save the file

doc.Save(xmlFile);

}

catch (Exception ex)

{

success = false;

}

return success;

}

The result will be

<?xml version="1.0" encoding="utf-8"?>

<Sms>

<Body>Good morning!</Body>

</Sms>

<Sms>

</Sms>

<Sms>

<Body>Updated Value</Body>

</Sms>

<Sms>

</Sms>

</SmsDataSet>

Delete XML values

Last thing to do, is learn how to remove a node. Once again we follow these simple steps.

Create an XMLDocument object.
Load the XML we want to update
Select the parent node out of which we will remove the node.
Select the node we are about to remove
Remove the selected node from the parent node
Save the XMLDocument object.

We want to delete the Sms node we created in the previous example. So, we select the parent SmsDataSet node and we remove the nodes we want ("/SmsDataSet/Sms[Id=3]") using the RemoveChild method.

bool DeleteXMLValues()

{

bool success = true;

try

{

string xmlFile = Server.MapPath("XMLFile.xml");

XmlDocument doc = new XmlDocument();

// Load the XML file into an XmlDocument.

doc.Load(xmlFile);

//Select the parent node

XmlNode node = doc.SelectSingleNode("/SmsDataSet");

//Select the node that will be deleted

XmlNodeList nodesToDelete = doc.SelectNodes("/SmsDataSet/Sms[Id=3]");

foreach (XmlNode nodeToDelete in nodesToDelete)

//Remove the node

node.RemoveChild(nodeToDelete);

//Since each node has unique Id, we could also use

//XmlNode nodeToDelete = doc.SelectSingleNode("/SmsDataSet/Sms[Id=3]");

//Remove the node

//node.RemoveChild(nodeToDelete);

//Save the file

doc.Save(xmlFile);

}

catch (Exception ex)

{

success = false;

}

return success;

}

As expected, the result is

<?xml version="1.0" encoding="utf-8"?>

<Sms>

<Body>Good morning!</Body>

</Sms>

<Sms>

</Sms>

<Sms>

<Body>Updated Value</Body>

</Sms>

</SmsDataSet>

Summary

This was the last article discussing XML handling. This time, we found out how we can update an XML file. We used XMLDocument to easily edit, insert and delete nodes by first selecting the appropriate nodes and then assign methods such as AppendChild or RemoveChild.

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