Play With First ()/FirstOrDefault () or Single ()/SingleOrDefault () in LINQ

Vijay Prativadi
Nov 19, 2012
21.7k
0
0
Article

Introduction

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

Question: What are these?

Please refer to the following table:

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="FirstandSingleLINQApp.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="Play with First/FirstOrDefault or Single/SingleOrDefault 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="First()" Font-Names="Verdana" Width="213px"
                            BackColor="Orange" Font-Bold="True" OnClick="Button1_Click" />
                    </td>
                </tr>
                <tr>
                    <td colspan="2" align="center">
                        <asp:Button ID="Button2" runat="server" Text="FirstOrDefault()" Font-Names="Verdana"
                            Width="213px" BackColor="Orange" Font-Bold="True" OnClick="Button2_Click" />
                    </td>
                </tr>
                <tr>
                    <td colspan="2" align="center">
                        <asp:Button ID="Button3" runat="server" Text="Single()" Font-Names="Verdana" Width="213px"
                            BackColor="Orange" Font-Bold="True" OnClick="Button3_Click" />
                    </td>
                </tr>
                <tr>
                    <td colspan="2" align="center">
                        <asp:Button ID="Button4" runat="server" Text="SingleOrDefault()" Font-Names="Verdana"
                            Width="213px" BackColor="Orange" Font-Bold="True" OnClick="Button4_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 FirstandSingleLINQApp
{
    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.First(); var querylist = new List<Employee> { query };
            GridView1.DataSource = querylist;
            GridView1.DataBind();
        }
        protected void Button2_Click(object sender, EventArgs e)|
        {
            var query = objEntities.Employee.FirstOrDefault();
            var querylist = new List<Employee> { query };
            GridView1.DataSource = querylist;
            GridView1.DataBind();
        }
        protected void Button3_Click(object sender, EventArgs e)
        {
            var query = objEntities.Employee.Single();
            var querylist = new List<Employee> { query };
            GridView1.DataSource = querylist;
            GridView1.DataBind();
        }
        protected void Button4_Click(object sender, EventArgs e)
        {
            var query = objEntities.Employee.Where(p => p.Age == 25).SingleOrDefault();
            var querylist = new List<Employee> { query };
            GridView1.DataSource = querylist;
            GridView1.DataBind();
        }
        #region Instance MembersCompanyEntities objEntities = new CompanyEntities();
        #endregion
    }
}

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

Step 5: The First () operation output of the application looks like this:

Step 6: The Single () operation output of the application looks like this (Here the sequence contains more than 1 element so throws up an exception):

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