.NET as it had evolved has come up with different API to read and write XML data. If you are using .NET 3.0 and lower version you will have to use XMLDocument aka the classic DOM API. With .NET 3.0 Microsoft had launched Language Integrated Query(LINQ) and with this came one of the feature name the LINQ to XML.
LINQ to XML has a simple model for building XML documents by hand. Whether it be XML sources from a stream or file, or XML created on-the-fly in code there are only a few important types to know and understand. The main ones used in everyday activities are XDocument, XElement and XAttribute.
In this article we will talk about XDocument and XMLDocument.
Lets consider the following test data for our article
<root>
<child id=’123′/>
<child id=’234′/>
…
</root>
Reading the XML
XmlDocument.Load
XmlDocument.Load was the cleanest and easiest to understand. It is necessary that you must know XPath, although the fact is I like XPath. XmlDocument does have some security concerns with XPath injection. Here is how we code to load a document
private static void XmlDocumentReader(string fileName) {
XmlDocument doc = new XmlDocument();
doc.Load(fileName);
XmlNodeList nodes = doc.SelectNodes(“//child”);
if (nodes == null) {
throw new ApplicationException(“invalid data”);
}
foreach (XmlNode node in nodes) {
string id = node.Attributes["id"].Value;
ProcessId(id);
}
}
Another way to query a single node is given below
XmlDocument doc = XmlDocument.Load(fileName);
XmlNode node = doc.SelectSingleNodes(“/root/child[@id=’123’")
LINQ to XML
LINQ to XML was also very easy to read and understand code. XDocument.Load does read the whole document into memory before returning. Due to feature of Lambda expression it has become very easy to traverse the xml document. The query syntax is easier than XPath or XQuery for developers who do not use XPath or XQuery on a daily basis. Here is the code I used to load and search the document:
private static void XDocumentReader(string fileName) {
XDocument doc = XDocument.Load(fileName);
if (doc == null | doc.Root == null) {
throw new ApplicationException("invalid data");
}
foreach (XElement child in doc.Root.Elements("child")) {
XAttribute attr = child.Attribute("id");
if (attr == null) {
throw new ApplicationException("invalid data");
}
string id = attr.Value;
ProcessId(id);
}
}
Another way to query a single node is given below
var xd = XDocument.Load(fileName);
var domQuery =
from c in xd.Descendants("child ")
where (string)c.Attribute("id") == "123"
Writing a new XML
Both the method almost looks similar.
XmlDocument
XmlDocument xmlDoc = new XmlDocument();
// Write down the XML declaration
XmlDeclaration xmlDeclaration = xmlDoc.CreateXmlDeclaration("1.0","utf-8",null);
// Create the root element
XmlElement rootNode = xmlDoc.CreateElement("root");
xmlDoc.InsertBefore(xmlDeclaration, xmlDoc.DocumentElement);
xmlDoc.AppendChild(rootNode);
// Create a new <child> element and add it to the root node
XmlElement parentNode = xmlDoc.CreateElement("child");
// Set attribute name and value!
parentNode.SetAttribute("ID", "01");
xmlDoc.DocumentElement.PrependChild(parentNode);
LINQ to XML
XDocument doc = new XDocument(
new XDeclaration("1.0", "utf-8", "yes"),
new XElement("root",
new XElement ("child", new XAttribute("id", "01")
)
);
Manipulating XML Data
XmlDocument
Here we have to struggle with manipulating the xml data. First take help of XPath to select the node and then use replace node to update it. Or use the feature of delete node and insert new node. Code is given below
XmlDocument doc = new XmlDocument.Load(fileName);
//Select the cd node with the matching title
XmlNode oldCd;
XmlElement root = doc.DocumentElement;
oldCd = root.SelectSingleNode("/root/child[id='1']“);
XmlElement newCd = doc.CreateElement(“child”);
newCd.SetAttribute(“id”,2);
root.ReplaceChild(newCd, oldCd);
//save the output to a file
doc.Save(fileName);
LINQ to XML
Here the code is very simple to write and understand. The coding time is also very less.
var xd = XDocument.Load(fileName);
var domQuery =
from c in xd.Descendants(“child “)
where (string)c.Attribute(“id”) == “123″
domQuery.Attribute(“id”).Value = 1
xd.save(filename)
Conclusion
Overall speaking both the API’s are equally powerful. However LINQ has made it little bit easier for developer to work with XML Data. I would say if you are using .NET 3.5 and higher you should rather go with LINQ To XML.
