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Inner Join Using LINQ For Multiple Tables (3 Tables Now) With Lambda

By Vijay Prativadi on October 22, 2012
Today, in this article let’s play around with one of the interesting and most useful concepts in LINQ.
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Introduction

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

Question: What is inner join using LINQ for multiple tables with lambda?

In simple terms "It provides flexibility to pull out the matching result sets from 3 or more tables with help of inner join using LINQ with lambda expression.".


Step 1: Create a new "ASP.NET Web Application", as in:
 

new-project-window.jpg
 

Step 2: The design of the Employee table looks like this:

 

employee-table.jpg
 

employee-ID-table.jpg
 

Step 3: The design of the Position table looks like this:

 

position-table.jpg
 

position-ID-table.jpg
 

Step 4: The design of the Salary table looks like this:
 

salary-table.jpg

 

salary-id-table.jpg


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

 

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="LINQInnerJoinApp._Default" %>

 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

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

    <title></title>

</head>

<body>

    <form id="form1" runat="server">

    <center>

        <div>

            <table>

                <tr>

                    <td colspan="2">

                        <asp:Label ID="Label1" runat="server" Text="INNER JOIN using LINQ for Multiple Tables (3 Tables) with Lambda"

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

                    </td>

                </tr>

                <tr>

                    <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>

                </tr>

                <tr>

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

                        <br />

                        <asp:GridView ID="GridView1" runat="server" BackColor="LightGoldenrodYellow" BorderColor="Tan"

                            BorderWidth="1px" CellPadding="2" EnableModelValidation="True" ForeColor="Black"

                            GridLines="None" AutoGenerateColumns="False">

                            <AlternatingRowStyle BackColor="PaleGoldenrod"></AlternatingRowStyle>

                            <FooterStyle BackColor="Tan"></FooterStyle>

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

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

                            </PagerStyle>

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

                            <Columns>

                                <asp:BoundField DataField="FirstName" HeaderText="First Name" ReadOnly="true" />

                                <asp:BoundField DataField="LastName" HeaderText="Last Name" />

                                <asp:BoundField DataField="Position1" HeaderText="Position" />

                                <asp:BoundField DataField="Salary1" HeaderText="Salary" />

                            </Columns>

                        </asp:GridView>

                    </td>

                </tr>

            </table>

        </div>

    </center>

    </form>

</body>

</html>

 

Step 6: 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 LINQInnerJoinApp

{

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

    {

        protected void Page_Load(object sender, EventArgs e)

        {

        }

        protected void Button1_Click(object sender, EventArgs e)

        {

            var query = objEntities.Employee.Join

            (

            objEntities.Position, r => r.EmpId, p => p.EmpId, (r, p) => new

            {

                r.FirstName,

                r.LastName,

                p.Position1,

                p.PosId

            }

            )

            .Join(objEntities.Salary, a => a.PosId, b => b.PosId, (a, b) => new

            {

                a.FirstName,

                a.LastName,

                a.Position1,

                b.Salary1

            });

            GridView1.DataSource = query;

            GridView1.DataBind();

        }

        #region Instance MembersCompanyEntities objEntities = new CompanyEntities();

        #endregion

    }

}

 

Step 7: The output of the application looks like this:

 

Inner-Join-operator-in-Linq.jpg


 

Step 8: The results retrieved output of the application looks like this:

  Output-Inner-Join-operator-in-Linq.jpg

Vijay Prativadi

Hey Everyone, It's Vijay. I am SDE mostly up on Microsoft Technologies. If you are thinking to know what I do mostly when at work. I get a chance to work upon few Microsoft technologies. All the way along my core tech... Read more

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