Co-related Queries and Self Join Using LINQ

Vijay Prativadi
12y
13k
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Article

Co-related Queries

Introduction

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

Question: What is co-related queries using LINQ?

In simple terms "It provides flexibility to perform co-relation of queries using LINQ".

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_RelatedQueriesLINQApp.WebForm1" %>
<!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">
    <style type="text/css">
        .grid
        {
            margin-top: 50px;
        }
    </style>
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <center>
        <div>
            <table>
                <tr>
                    <td colspan="2" align="center">
                        <asp:Label ID="Label1" runat="server" Text="Co-related Queries using LINQ" 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">
                        <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" />
                        </asp:GridView>
                    </td>
                </tr>
            </table>
        </div>
    </center>
    </form>
</body>
</html>

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_RelatedQueriesLINQApp
{
    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.Employeewhere
                         r.Location == (from q in objEntities.Department
                         where q.Location == r.Location select q.Location).FirstOrDefault()select
                         new{FirstName = r.FirstName,LastName = r.LastName,Age = r.Age,Location = r.Location});
            GridView1.DataSource = query;
            GridView1.DataBind();
        }
        #region Instance MembersCompanyEntities objEntities = new CompanyEntities();
        #endregion
    }
}

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

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

Self Join

Question: What is self join using LINQ?

In simple terms "It provides the flexibility to perform a join on a single table and get the result set based on the request query".

Step 1: Create a new WebForm project

Step 2: The complete code of WebForm1.aspx looks like this:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="SelfJoinApp.WebForm1" %>
<!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">
    <style type="text/css">
        .grid
        {
            margin-top: 50px;
        }
    </style>
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <center>
        <div>
            <table>
                <tr>
                    <td colspan="2" align="center">
                        <asp:Label ID="Label1" runat="server" Text="Self Join using LINQ" 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">
                        <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" />
                        </asp:GridView>
                    </td>
                </tr>
            </table>
        </div>
    </center>
    </form>
</body>
</html>

Step 3: 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 SelfJoinApp
{
    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.Employeejoin q in objEntities.Employee on r.ManagerId
                equals q.EmpIdselect new{FirstName = r.FirstName,
                LastName = r.LastName,ManagerName = string.Concat(q.FirstName, " ", q.LastName)}).ToList();
            GridView1.DataSource = query;
            GridView1.DataBind();
        }
        #region Instance MembersCompanyEntities objEntities = new CompanyEntities();
        #endregion
    }
}

Step 4: The output of the application looks like this:

Step 5: The data retrieved output of the application looks like this:

I hope this article is useful for you. I look forward for your comments and feedback.Thanks Vijay Prativadi

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