Three Layer

<configuration>

  <connectionStrings>

    <add name="Mythreetier" connectionString="Data Source=guru\sqlexpress;Initial Catalog=ProjectBilling;Integrated Security=True" providerName="System.Data.SqlClient"/>

  </connectionStrings>

</configuration>

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Configuration;

using System.Data;

using System.Data.SqlClient;

namespace DatabaseLayer

{

    public class clsDataLayer

    {

    private string conn = ConfigurationManager.ConnectionStrings["Mythreetier"].ToString();

 

        public void InsertUpdateDeleteSQLString(string sqlstring)

        {

            SqlConnection objsqlconn = new SqlConnection(conn);

           if (objsqlconn.State == ConnectionState.Closed)

            {

                objsqlconn.Open();

            }           

            SqlCommand objcmd = new SqlCommand(sqlstring, objsqlconn);

            objcmd.ExecuteNonQuery();

        }

 

        public object ExecuteSqlString(string sqlstring)

        {

            SqlConnection objsqlconn = new SqlConnection(conn);

            if (objsqlconn.State == ConnectionState.Closed)

            {

                objsqlconn.Open();

            }  

            DataSet ds = new DataSet();

            SqlCommand objcmd = new SqlCommand(sqlstring, objsqlconn);

            SqlDataAdapter objAdp = new SqlDataAdapter(objcmd);

            objAdp.Fill(ds);

            return ds;

        }

    }

}

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using DatabaseLayer

namespace BusinessLayer

{

    public class clsBusinessLayer

    {

        public clsDataLayer objDataLayer = new clsDataLayer();

        public void AddNewCustomer(string custname, string custaddr, string custcountry, string custcity, string custincode)

        {

            objDataLayer.AddNewCustomerDB(custname, custaddr, custcountry, custcity, custincode);

        }

        public void UpdateCustomer(int custid, string custname, string custaddr, string custcountry, string custcity, string custincode)

        {

            objDataLayer.UpdateCustomerDB(custid, custname, custaddr, custcountry, custcity, custincode);

        }

 

        public void DeleteCustomer(int custid)

        {

            objDataLayer.DeleteCustomerDB(custid);

        }

        public object LoadCustomer()

        {

            return objDataLayer.LoadCustomerDB();

        }

    }

}