C# 4 and .NET 4

976 ❘ ChaPTer 34 .net prOGrAmminG with sQl server
}
class Program
{
static void Main()
{
using (ExamsEntities data = new ExamsEntities())
{
foreach (Exam item in db.Exams)
{
XElement exam = XElement.Parse(item.Info);
Console.WriteLine("Exam: {0}", exam.Attribute("Number").Value);
Console.WriteLine("Title: {0}", exam.Element("Title").Value);
Console.Write("Course(s): ");
foreach (var course in exam.Elements("Course"))
{
Console.Write("{0} ", course.Value);
}
Console.WriteLine();
}
}
}
}
The ADO.NET Entity Framework and LINQ to XML are explained in Chapter 31, “ADO.NET Entity
Framework,” and Chapter 33, “Manipulating XML,” respectively.
querying the data
Up until now, you haven’t seen the really great features of the XML data type. SQL SELECT statements can
be combined with XML XQuery.
A SELECT statement combined with an XQuery expression to read into the XML value is shown here:
SELECT [Id], [Number], [Info].query('/Exam/Course') AS Course FROM [Exams]
The XQuery expression /Exam/Course accesses the Course elements that are children of the Exam
element. The result of this query returns the IDs, exam numbers, and courses:
1 70-502 6460
2 70-562 23106463
3 70-561 23106464
With an XQuery expression, you can create more complex statements to query data within the XML
content of a cell. The next example converts the XML from the exam information to XML that lists
information about courses:
SELECT [Info].query('
for $course in /Exam/Course
return
{ data(/Exam[1]/@Number) }
{ data($course) }
')
AS Course
FROM [Exams]
WHERE Id=2
Here, just a single row is selected with SELECT [Info]. FROM Exams WHERE Id = 2. With the result
of this SQL query, the for and return statements of an XQuery expression are used. for $course
in /Exam/Course iterates through all Course elements. $course declares a variable that is set with every
iteration (similar to a C# foreach statement). Following the return statement, the result of the query for
every row is defined. The result for every course element is surrounded by the element. Embedded
inside the element are and . The text within the element is defined with
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