Creating and transforming XML using LINQ

XML has achieved tremendous adoption as a basis for formatting data whether in Word files, in configuration files, or in databases; XML seems to be everywhere. Yet, from a development perspective, XML is still hard to work with. If you ask the average software developer to work in XML you will likely hear a heavy sigh. The API choices for working with XML seem to be either aged and verbose such as DOM or XML specific such as XQuery or XSLT which require motivation, study, and time to master. LINQ to XML, a component of the LINQ project, aims to address this issue. LINQ to XML is a modernized in-memory XML programming API designed to take advantage of the latest .NET Framework language innovations. It provides both DOM and XQuery/XPath like functionality in a consistent programming experience across the different LINQ-enabled data access technologies.

In this article I will explore some of the features available in .NET Framework release 3.5 related to LINQ for XML. This is, of course, not an extensive discussion, merely a familiarization and stepping stone for more learning and exploration.

Let’s start with one of the old ways of creating the xml. Then later on I will explain how the same can be written using new LINQ to XML API.

Old WAY of doing things

public void CreateEmployeesOld()
{
XmlElement root = m_doc.CreateElement("employees");
root.AppendChild(AddEmployee(1, "John doe", DateTime.Parse("12/12/2005"), true));
root.AppendChild(AddEmployee(2, "Kim", DateTime.Parse("11/23/1999"), true));
root.AppendChild(AddEmployee(3, "Carla", DateTime.Parse("2/6/2008"), false));
root.AppendChild(AddEmployee(4, "Aleks", DateTime.Parse("10/6/1998"), false));
m_doc.AppendChild(root);
Response.Write(m_doc.OuterXml);
}

private static XmlElement AddEmployee(int ID, string name, DateTime hireDate, bool isSalaried)
{
XmlElement employee = m_doc.CreateElement("employee");
XmlElement nameElement = m_doc.CreateElement("name");
nameElement.InnerText = name;
XmlElement hireDateElement = m_doc.CreateElement("hire_date");
hireDateElement.InnerText = hireDate.ToShortDateString();
employee.SetAttribute("id", ID.ToString());
employee.SetAttribute("salaried", isSalaried.ToString());
employee.AppendChild(nameElement);
employee.AppendChild(hireDateElement);
return employee;
}

Now say for, once you have created the employee xml and now you want to transform it to new set of xml elements, then old way need help of XSLT. But in below example of LINQ to XML I have explained that too. How easy it would be to transform one xml to another one without using XSLT

New WAY of doing things

public void CreateEmployeesNew()
{
// creating employee xml
XDocument doc = new XDocument(
new XDeclaration("1.0", "utf-8", "yes"),
new XComment("A sample xml file"),
new XElement("employees",
new XElement("employee",
new XAttribute("id", 1),
new XAttribute("salaried", "true"),
new XElement("name", "John doe"),
new XElement("hire_date", "12/12/2005")),
new XElement("employee",
new XAttribute("id", 2),
new XAttribute("salaried", "true"),
new XElement("name", "Kim"),
new XElement("hire_date", "11/23/1999")),
new XElement("employee",
new XAttribute("id", 3),
new XAttribute("salaried", "false"),
new XElement("name", "Carla"),
new XElement("hire_date", "2/6/2008")),
new XElement("employee",
new XAttribute("id", 4),
new XAttribute("salaried", "false"),
new XElement("name", "Aleks"),
new XElement("hire_date", "10/6/1998"))
)
);
Response.Write("
" + doc + "
");

// transforming employee xml in to newer xml format.
XElement element = new XElement("salaried_employees", from e in doc.Descendants("employee")
where e.Attribute("salaried").Value == "true"
select new XElement("employee",
new XElement(e.Element("name"))));
Response.Write("
" + element + "
");
}

To conclude this I would say, XML is fantastic construct that has been deeply ingrained into just about everything. Having the ability to easily construct, query, transform and manipulate XML documents is an invaluable service that will improve the speed of which applications can be built and the quality of those applications.This article is not an exhaustive investigation of LINQ to XML; there have been many other articles, snippets and blogs written on the subject. It mainly just a taste and familiarization of what is possible using .NET 3.5.