Self-Join Using LINQ

Vijay Prativadi
Mar 04, 2013
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Article

Introduction

This article demonstrates an interesting and very useful concept in LINQ.

Question: What is self-join using LINQ?

In simple terms "It enables selection of data by performing a self-join on a table using LINQ query".

Step 1: Create a new web application

Step 2: Add a new Entity Framework

Step 3: The complete code of WebForm1.aspx is as in the following:

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

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

.grid

{

margin-top: 50px;

}

</style>

</head>

<body>

<div>

<table>

<tr>

<asp:Label ID="Label1" runat="server" Text="Self Join with LINQ" Font-Bold="true"

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

</td>

</tr>

<tr>

<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>

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

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

AutoGenerateColumns="True">

</asp:GridView>

</td>

</tr>

</table>

</div>

</center>

</form>

</body>

</html>

Step 4: The complete code of WebForm1.aspx.cs is as in the following:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;namespace SelfJoin_LINQ

{

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 = from r in objEntities.tblEmployee join q in objEntities.tblEmployee on r.Id equals q.EmpRoleId select new

{

Id = r.FirstName + " " + r.LastName, RoleEmployees = q.FirstName + " " + q.LastName };

GridView1.DataSource = query;

GridView1.DataBind();

}

#region Instance MembersCompanyEntities objEntities = new CompanyEntities();

#endregion

}

}

Step 5: The output of the application is as in the following:

Step 6: The selected data output of the application is as in the following:

I hope this article was useful for you.