ARTICLE

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

Posted by Vijay Prativadi Articles | LINQ 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

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