LINQ QUerry : A Step Ahead Series

LINQ Query : A Step Ahead Series

History:
The article is related to previous posts :

1. Anonymous Types in LINQ: A Step Ahead Series

2. How to Test Anonymous Type Equality - LINQ: A Step Ahead Series

Introduction:

LINQ - Language Integreted Query is repeadily used in these days. The presented article is elaborate the idea "How to describe a LINQ Query".

Simply, a query is an expression that retrieves data from a data source.

Scope:

The scope of the presented article is upto its title and projected scenarios.

• Basics


• LINQ Actions


• Some basic example


• Creating a LINQ project using Visual Studio

class LINQQuery
{        
    static void Main()
    {
        
        //  This is the Data source - Operation - I
        int[] numbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };

        //  Query Creation - Operation - II
        var numQuery =
            from num in numbers
            where (num % 2) == 0
            select num;

        //  Query Execution - Operation - III
        foreach (int num in numQuery)
        {
            Console.Write("{0,1} ", num);
        }
    }
}

1. In Visual Studio, open a Visual Basic or C# project that was created in Visual Studio 2005 and follow the prompts to convert it to a Visual Studio 2008 project.


2. For a C# project, click the Project menu, and then click Properties.


3. In the Application property page, select .NET Framework 3.5 in the Target Framework drop-down list.


4. For a Visual Basic project, click the Project menu, and then click Properties.


5. In the Compile property page, click Advanced Compile Options and then select .NET Framework 3.5 in the Target Framework (all configurations) drop-down list.

1. LINQ queries start with the keyword from.


2. In a LINQ query, you are always working with objects.


3. You an apply the basic operations to LINQ Query as follow:
   
   
   
   • 
     
     Filtering is the common operation tyhrough which you can filter the data, consider following code:
     
     

     
     //filter all employees on last name as 'Arora'
     var lnqueryNames = from empname in employee
                                where empname.lastname == "Arora"
                                select empname;
     

     
     
   
   
   Ordering sets the ordering for the output, lets take a loon in the following:
   
   

   
   //display all Arora in ascending order with departments
   var lnqueryNames = from empname in employee
                              where empname.lastname == "Arora"
                              orderby empname.dept ascending
                              select empname;
   

   
   
   
   • 
     Ordering give the output in a group, consider following example:
     
     

     
     
     var lnqueryNames = from empname in employee
                                group empname by empname.department;
     
     foreach (var empbydept in lnqueryNames)
       {
           Console.WriteLine(empbydept.Key);
           foreach (Employee emp in empbydept)
           {
               Console.WriteLine("    {0}", emp.lastName);
           }
       }