How to use LINQ syntax to query data

Language Integrated Query (LINQ) is possibility the most exciting new feature Microsoft added that first introduced in Visual Studio 2008 and .NET Framework version 3.5.

Language Integrated Query (LINQ) has its own capability in querying a data from database, flexibility and overwhelming reach of LINQ to change the way developers write application. Nevertheless, LINQ is a powerful strongly typed syntax for accessing queries and generating results which improves developer productivity to write less code that create a better application. For more information visit MSDN LINQ.

Actually, when I first explore this language it looks weird and feels none – sense. Indeed, it helps saves a lot of works. So far, I’m still learning about this language and publish it as my own future reference at the same time providing relevant information for those trying to learn LINQ. In this tutorial, it shows how to use queries using LINQ.

Creating simple LINQ Queries using select, from, where, orderby, and join keywords.

First of all, I’ll show you a basic LINQ query and for the next tutorial we’re going to work with databases queries. For now it’s simply a sort of a given array form.

     string[] queryString = { "LINQ", "VB.NET", "C#", "ASP.NET", "C++" };

            var str = from strquery in queryString

                      select strquery;

            foreach (var data in str)

            {

                listBox1.Items.Add(data);      

            }

Output:

LINQ

VB.NET

C#

ASP.NET

C++

In this example it sorts alphabetically with orderby keyword.

     string[] queryString = { "LINQ", "VB.NET", "C#", "ASP.NET", "C++" };

            var str = from strquery in queryString

                      orderby strquery            

                      select strquery;

            foreach (var data in str)

            {

                listBox1.Items.Add(data);      

            }

Output:

ASP.NET

C#

C++

LINQ

VB.NET

In this example it shows only specific result with where keyword.

     string[] queryString = { "LINQ", "VB.NET", "C#", "ASP.NET", "C++" };

            var str = from strquery in queryString

                      where strquery == "LINQ"

                      orderby strquery            

                      select strquery;

            foreach (var data in str)

            {

                listBox1.Items.Add(data);      

            }

Output:

LINQ

In this example it will display a number from 1 to 5

     int[] number = { 1, 2, 3, 4, 5 };

            var num = from querynum in number

                      select querynum;

            foreach (var mynumber in num)

            {

                listBox1.Items.Add(mynumber);

            }

Output:

1

2

3

4

5

In this example use join keyword to join two arrays and display the same element of both arrays.

     int[] num1 = { 1, 2, 3, 4, 5 };

            int[] num2 = { 1, 3, 7, 9, 5 };

            var joinNum = from queryNum1 in num1

                          join queryNum2 in num2

                          on queryNum1 equals queryNum2

                          select new {queryNum1,queryNum2};

            foreach (var myjoin in joinNum)

            {

                listBox1.Items.Add(myjoin);

            }

Output:

{queryNum1 = 1, queryNum2 = 1}

{queryNum1 = 3, queryNum2 = 3}

{queryNum1 = 5, queryNum2 = 5}

When you noticed the output contains three array elements 1, 3, and 5 that compare num1 and num 2 Array. However there’s other way how to construct join statement, instead with join, they use from, here is sample code.

     var fromjoin = from queryA in arrayA

                           from queryB in arrayB

                           where queryA == queryB

                           select new { queryA, queryB };

It will generate the same output as what join statement stated.

If you are newbie using LINQ and didn’t know yet, but it has already background either VB.NET or C#, don’t worry because .NET 3.5+ has a build – in function that supports query syntax. Unfortunately, lower version of .NET doesn’t support LINQ.