check if id exists in database c#

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In this article I will explain how to check if Id already exists in DB.
Out Put Looks Like This.

I created a New Project in windows form using c#

Now in Form1.cs, I designed my UI

I created a table name Employee in my database.

Now i am creating the Stored Procedure for Inserting the data in database.                                                     

USE [dotnetdb]
GO

/****** Object:  StoredProcedure [dbo].[SP_InsertEmpinfo]    Script Date: 07/23/2013 13:54:06 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

Create procedure [dbo].[SP_InsertEmpinfo]
(
@EmpId nvarchar(50),
@EmpName nvarchar(50),
@EmpAddress nvarchar(50),
@EmpDesignation nvarchar(50)
)

As Begin

Insert into Employee (EmpId,EmpName,EmpAddress,EmpDesignation) values (@EmpId,@EmpName,@EmpAddress,@EmpDesignation)
end

GO

Now i am writing the code on buttonclick in Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace CheckId
{
    public partial class Form1 : Form
    {
     public  string empid;
        
        public Form1()
        {
            InitializeComponent();
        }

        private void submit_Click(object sender, EventArgs e)
        {
            using (SqlConnection con = new SqlConnection("Data Source = CHINNU;Initial Catalog = dotnetdb;Uid = sa;Password = password123;"))
            {

                if (!empId())
                {
                }

                else
                {
                    SqlCommand cmd = new SqlCommand("SP_InsertEmpinfo", con);
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.Add("@EmpId", SqlDbType.NVarChar).Value = txtempid.Text;
                    cmd.Parameters.Add("@EmpName", SqlDbType.NVarChar).Value = txtempname.Text;
                    cmd.Parameters.Add("@EmpAddress", SqlDbType.NVarChar).Value = txtempaddress.Text;
                    cmd.Parameters.Add("@EmpDesignation", SqlDbType.NVarChar).Value = txtdesignation.Text;
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();
                }
            }  
        }


        public bool empId()
        {

            using (SqlConnection con = new SqlConnection("Data Source = CHINNU;Initial Catalog = dotnetdb;Uid = sa;Password = password123;"))
            {
                con.Open();

                string query = "select EmpId from employee where EmpId= '" + txtempid.Text + "'";

                SqlCommand cmd = new SqlCommand(query, con);

                SqlDataReader dr;

                dr = cmd.ExecuteReader();

                while (dr.Read())
                {

                    empid = dr["EmpId"].ToString();

                    if (empid != "0")
                    {

                        MessageBox.Show("Id Already Exists");

                        return false;
                    }
                    con.Close();
                }


                return true;
            }
        }

                
    }
}

Now I am adding App.config for Connection.

Now Press F5.

Now I am Entering the employee information as shown below.

Now i inserted the employee information in my db,again i am trying to inserting the same information.

  It throws an error message like this.                                                                                                           

Output:                                                                                                                                                            

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