This code is written using
LINQ Preview May 2006 CTP.
To run this sample code, you
must have
Visual Studio
2005
Express or other Visual Studio 2005 versions.
After that, install LINQ
Preview May 2006 CTP version from MSDN website.
After installation
of LINQ Preview May 2006 CTP, click on New Project in the File menu of
Visual
Studio
2005, select LINQ Preview in the Project Types and create a LINQ Console
Application from the selected templates.
Note:
If you want to write your sample code in VB.NET, Select Visual Basic in
the Project types and LINQ in the Templates pane.
See Figure 1.
Figure 1.
As name suggests, LINQ (.NET
Integrated Query Language) provides from..where..select syntax to select
data
from collections.
Understanding
from..where..select
The from..where..select
syntax in LINQ is similar to SELECT..FROM..WHERE clause of SQL. Here is a simple
from..select.
from day in
daysArray
select day;
In the above
statement, I select day in daysArray. It returns an object of "var" type, which
is a generic type and can store any type. For example, daysArray can be an array
of numbers, strings, or even objects. Here is an example of daysArray.
string[] daysArray = {
"Mon",
"Tue", "Wed",
"Thur",
"Fri", "Sat",
"Sun" };
This is how
return value is stored from a from..select statement.
var days =
from day in daysArray
select day;
Now where
clause is used to filter the results. For example, the following syntax gets
retuslts from daysArray where value of day is "Wed" only.
var days =
from day in daysArray
where day =="Wed"
select day;
Filtering using where
The following code selects
items from an array that have value below 20.
int[]
IntArray = { 12, 5, 24, 10, 9, 8, 4, 87, 23, 7, 11, 43 };
var under20 =
from u20 in
IntArray where u20 < 20
select u20;
Console.WriteLine("Numbers
below 20 are: ");
Console.WriteLine("=====================");
foreach (var numU20 in under20)
{
Console.WriteLine(numU20);
}
Console.WriteLine("======================");
Console.ReadLine();
The output looks like Figure
2.
Figure 2.
The following query is used
to get items between two values, greater than 8 and less than 20.
var
under20 = from u20
in IntArray where u20 < 20 && u20 > 8
select u20;
The output looks like Figure
3.
Figure 3.
The exact match items can be
retrieved using == operator. For example, the following syntax selects items
that have value 23.
var
under20 = from u20
in IntArray where u20 == 23
select u20;
The output looks like Figure
4.
Figure 4.