C# 5.0 Programmer's Reference

192 ❘ CHAPTER 8 LINQ
For example, suppose a program has an array named employees that contains Employee objects.
The following code uses LINQ and functional construction to build an XML fragment containing
elements for each of the Employee objects.
// Use LINQ to create a list of elements.
var makeEmployees =
from employee in employees
select new XElement("Employee",
new XAttribute("FirstName", employee.FirstName),
new XAttribute("LastName", employee.LastName));
// Create the XML document.
XElement document = new XElement("Employees", makeEmployees);
The code starts with a LINQ query that selects information from the employees array. For each
Employee in the array, the query creates an XElement. It uses the Employee object’s FirstName and
LastName properties to create XAttribute objects for the XElement.
You can even include the LINQ query directly inside the top-level constructor, as shown in the
following code.
XElement document2 = new XElement("Employees",
from employee in employees
select new XElement("Employee",
new XAttribute("FirstName", employee.FirstName),
new XAttribute("LastName", employee.LastName)));
LINQ out of XML
The LINQ XML objects provide a standard assortment of LINQ methods that make moving data
from those objects into IEnumerable objects simple. Using these functions, it’s about as easy to
select data from the XML objects as it is from IEnumerable objects such as arrays and lists.
XML objects represent hierarchical data. To make using that data easier, the XML classes also
provide methods to help you search those data hierarchies. For example, the XElement object provides
a Descendants method that searches the object’s descendants for elements of a certain type.
For example, the following code searches the XElement named document for descendants named
“Employee” and displays their FirstName and LastName attributes.
var selectEmployee =
from employee in document.Descendants("Employee")
select new
{
FirstName = employee.Attribute("FirstName").Value,
LastName = employee.Attribute("LastName").Value
};
foreach (var obj in selectEmployee)
Console.WriteLine(obj.FirstName + " " + obj.LastName);
The LINQ query selects objects from document.Descendants("Employee"). Each of the objects
returned by the Descendants method is an XElement. The query uses that object’s Attribute method
to get the object’s FirstName and LastName attributes. Those attributes are XAttribute objects, so
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