ASP.NET

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using BookStoreBLL;
using System.Collections.Generic;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
            return;
        BooksBLL bll = new BooksBLL("C");
        Book[] books = bll.allBooks();
        GridView1.DataSource = books;

        
    }
    
}

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

namespace BookStoreWindowsForms
{
    public partial class Form1 : Form
    {
        
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            BooksBLL bll = new BooksBLL("C");
            Book[] books = bll.allBooks();
            dataGridView1.DataSource = books;
            
            
        }        
    }
}

using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using BookStoreDAL;
using System.Data.Common;

namespace BookStoreBLL
{

    public class BooksBLL
    {
        private DALClass dal;
        public BooksBLL(string conStr)
        {
            dal = new DALClass(conStr);
        }

        public Book[] allBooks()
        {
            string sql = "SELECT * FROM Books";
            List<book> allBooks = new List<book>();
            dal.Open();
            DbDataReader reader = dal.ExecuteReader(sql);
            if (reader != null)
            {
                while (reader.Read())
                {
                    Book book = new Book();
                    book.BookCode = (int)reader["ID"];
                    book.BookName = (string)reader["BookName"];
                    book.Publisher = (string)reader["Publisher"];
                    book.Price = (decimal)reader["price"];
                    book.BooksInStock = (int)reader["AmountInStock"];
                }
                reader.Close();
            }
            dal.Close();


            return allBooks.ToArray();
        }
    }
}</book></book>

using System;
using System.Collections.Generic;
using System.Text;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;
using System.Data.Common;
using System.Data.OleDb;


namespace BookStoreDAL
{
    public class DALClass
    {
        private string conStr;
        private DbConnection con;
        private DbCommand com;
        private string dbType;

        public DALClass(string conStrName)
        {
            //System.Diagnostics.Debugger.Break();
            conStr = ConfigurationManager.ConnectionStrings[conStrName].ConnectionString;
            dbType = ConfigurationManager.ConnectionStrings[conStrName].ProviderName;

            if (dbType == "System.Data.SqlClient")
            {
                con = new SqlConnection(conStr);
                com = new SqlCommand();
            }
            else if (dbType == "System.Data.OleDb")
            {
                con = new OleDbConnection(conStr);
                com = new OleDbCommand();
            }
            com.Connection = con;
        }

        public bool Open()
        {
            try
            {
                if (con.State != ConnectionState.Open)
                    con.Open();
                return true;
            }
            catch
            {
                return false;
            }
        }

        public void Close()
        {
            con.Close();
        }

        public DbDataReader ExecuteReader(string sql)
        {
            try
            {
                com.CommandText = sql;
                DbDataReader reader = com.ExecuteReader();
                return reader;
            }
            catch
            {
                return null;
            }
        }

        public bool ExecuteNonQuery(string sql)
        {
            try
            {
                com.CommandText = sql;
                com.ExecuteNonQuery();
                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }

        public DbDataReader ExecuteReader(DbParameter[] parameters, string sql)
        {
            try
            {
                com.CommandText = sql;
                com.Parameters.AddRange(parameters);
                DbDataReader reader = com.ExecuteReader();
                com.Parameters.Clear();
                return reader;
            }
            catch
            {
                return null;
            }
        }

        public DbParameter CreateDbParameter(string name, object value)
        {
            DbParameter param = null;
            if (dbType == "System.Data.SqlClient")
                param = new SqlParameter();
            else if (dbType == "System.Data.OleDb")
                param = new OleDbParameter();

            param.ParameterName = name;
            param.Value = value;
            return param;
        }
    }
}