Database component: It consists of following files:
i)   IDbCommand.cs
ii)  AbstractCommand.cs
iii) MSSqlDbComponent.cs

Build the above files and create : mssqldbcomponent.dll

file name: IDbCommand.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace teacherone.mssqldbcomponent
{
    interface IDbCommand
    {
        void Execute();
    }
}


file name: AbstractCommand.cs 

using System;
using System.Collections.Generic;
using System.Text;
using System.Data.SqlClient;
using System.Xml;

namespace teacherone.mssqldbcomponent
{
    public class AbstractCommand
    {
        private SqlConnection connection;
        private SqlTransaction transaction;

        protected string command;
        protected string commandtype;
        protected string result;
        protected string connectionString;

        public void setCommand(string pcommand, string pcommandtype)
        {
            command = pcommand;
            commandtype = pcommandtype;
        }

        public void Flush()
        {
            command = null;
            commandtype = null;
            result = null;
        }

        public void Dispose()
        {
            command = null;
            commandtype = null;
            result = null;
            connectionString = null;

            if (transaction != null)
            {
                transaction.Dispose();
                transaction = null;
            }
            if (connection != null)
            {
                connection.Close();
                connection.Dispose();
                connection = null;
            }
        }

        public void Execute()
        {
            if (connection == null)
            {
                connection = new SqlConnection(connectionString);
                connection.Open();
            }
            SqlCommand sqlcommand = new SqlCommand(command, connection);
            sqlcommand.Transaction = transaction;

            if (commandtype.Equals("INSERT") ||
                 commandtype.Equals("UPDATE") ||
                 commandtype.Equals("DELETE"))
            {
                result = "" + sqlcommand.ExecuteNonQuery();
            }
            else
            {
                XmlReader xmlreader = sqlcommand.ExecuteXmlReader();
                if (xmlreader.Read())
                {
                    result = xmlreader.ReadOuterXml();
                }
                else
                {
                    result = null;
                }
                xmlreader.Close();
                xmlreader = null;
                sqlcommand = null;
            }
            command = string.Empty;
            commandtype = string.Empty;
        }


        public void StartTransaction()
        {
            connection = new SqlConnection(connectionString);
            connection.Open();
            transaction = connection.BeginTransaction();
        }

        public void EndTransaction()
        {
            transaction.Commit();
            transaction.Dispose();
        }

        public void RollBackTransaction()
        {
            transaction.Rollback();
            transaction.Dispose();
        }

    }
}



file name: MSSqlDbComponent.cs 


using System;
using System.Collections.Generic;
using System.Text;

namespace teacherone.mssqldbcomponent
{
    public class MSSqlDbComponent : AbstractCommand, IDbCommand
    {
        public MSSqlDbComponent()
        {
        }
        public void SetConnectionString(string connstr)
        {
            connectionString = connstr;
        }

        public string GetResult()
        {
            return result;
        }

    }
}

Testing of database component

Create the table.

USE [SomeDatabaseDB]
GO
/****** Object:  Table [dbo].[classified]    Script Date: 01/01/2008 01:01:01 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[classified](
	[classifiedid] [int] NULL,
	[classifieddesc] [ntext] NULL,
	[classifiedtype] [int] NULL,
	[createdate] [datetime] NULL
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]



Client program to test the database component: 



file name: TestClient.cs 

While compiling TestClient.cs make reference to mssqldbcomponent.dll 
(it was created using IDbCommand.cs, AbstractCommand.cs and MSSqlDbComponent.cs)


using System;
using System.Collections.Generic;
using System.Text;
using teacherone.mssqldbcomponent;

namespace TestClient
{
    class Program
    {
        static void Main(string[] args)
        {
            string connectionstring = 
              @"Data source=computername\SQLEXPRESS;Initial Catalog=SomeDatabaseDB; Integrated Security=SSPI";

            MSSqlDbComponent dbcomponent = new MSSqlDbComponent();
            dbcomponent.SetConnectionString(connectionstring);


            /// Demo: Inser command
            string insertcommand = " insert into classified (classifiedid, classifieddesc, " +
                                   " classifiedtype,classifiedtype. createdate) " +
                                   " values " +
                                   " (2,'test descr',2,'11/12/2008') " ;

            dbcomponent.setCommand(insertcommand, "INSERT");
            dbcomponent.Execute();

            /// Demo: select command
            string selectcommand = " select * from  classified  FOR XML AUTO, TYPE ";

            dbcomponent.setCommand(selectcommand, "SELECT");
            dbcomponent.Execute();
            string result = dbcomponent.GetResult();
            Console.WriteLine(result);

            Console.WriteLine("Hit enter to continue...");
            Console.Read();


        }
    }
}