Correlated Query Operation With Lambda Operator in C#


Today, in this article let's play around with one of the interesting and most useful concepts in C# with Lambda.

Question: What is correlated query operation with Lambda operator (=>) in C#?

In simple terms "It provides the ability to perform a correlated query operation with a Lambda operator in C#".

Step 1: Create a new WebForm project

Step 2: The employee table output of the application looks like this:


Step 3: The department table output of the application looks like this:


Step 4: The complete code of WebForm1.aspx looks like this:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="Co_related_Operation_Lambda_App.WebForm1" %>


<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">

<html xmlns="">

<head id="Head1" runat="server">

    <style type="text/css">



            margin-top: 50px;






    <form id="form1" runat="server">





                    <td colspan="2" align="center">

                        <asp:Label ID="Label1" runat="server" Text="Correlated Queries using Lambda Operator (=>)"

                            Font-Bold="true" Font-Size="Large" Font-Names="Verdana" ForeColor="Maroon"></asp:Label>




                    <td colspan="2" align="center">

                        <asp:Button ID="Button1" runat="server" Text="Select Data" Font-Names="Verdana" Width="213px"

                            BackColor="Orange" Font-Bold="True" OnClick="Button1_Click" />




                    <td colspan="2" align="center">

                        <asp:GridView ID="GridView1" runat="server" CssClass="grid" BackColor="LightGoldenrodYellow"

                            BorderColor="Tan" BorderWidth="1px" CellPadding="2" ForeColor="Black" GridLines="None">

                            <AlternatingRowStyle BackColor="PaleGoldenrod" />

                            <FooterStyle BackColor="Tan" />

                            <HeaderStyle BackColor="Tan" Font-Bold="True" />

                            <PagerStyle BackColor="PaleGoldenrod" ForeColor="DarkSlateBlue" HorizontalAlign="Center" />

                            <SelectedRowStyle BackColor="DarkSlateBlue" ForeColor="GhostWhite" />

                            <sortedascendingcellstyle backcolor="#FAFAE7" />

                            <sortedascendingheaderstyle backcolor="#DAC09E" />

                            <sorteddescendingcellstyle backcolor="#E1DB9C" />

                            <sorteddescendingheaderstyle backcolor="#C2A47B" />










Step 5: The complete code of WebForm1.aspx.cs looks like this:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace Co_related_Operation_Lambda_App


    public partial class WebForm1 : System.Web.UI.Page


        protected void Page_Load(object sender, EventArgs e)



        protected void Button1_Click(object sender, EventArgs e)


            var query = objEntities.Employee.Where(r => r.Location == objEntities.Department.Where(q => q.Location == r.Location).Select(q => q.Location).FirstOrDefault()).Select(r => new { FirstName = r.FirstName, LastName = r.LastName, Age = r.Age, Location = r.Location });

            GridView1.DataSource = query; GridView1.DataBind();


        #region Instance

        MembersCompanyEntities objEntities = new CompanyEntities();




Step 6: The output of the application looks like this:

Step 7: The co-relation operation with Lambda output of the application looks like this: