using System;

using System.Collections.Generic;

using System.Text;

using System.Data;

using System.Data.OleDb;

namespace BaiThi.DungChung

{

    class thaotacdb

    {

        public static OleDbConnection ketnoi()

        {

            return new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=E:\DataKTHT.mdb");

        }

        public static void ThucHien(string SQL)

        {

            OleDbConnection conn = ketnoi();

            conn.Open();

            OleDbCommand cmd = new OleDbCommand(SQL, conn);

            cmd.ExecuteNonQuery();

            conn.Close();

        }

        public static DataSet LayDataset(string SQL)

        {

            OleDbConnection conn = ketnoi();

            conn.Open();

            OleDbDataAdapter ad = new OleDbDataAdapter(SQL, conn);

            DataSet ds = new DataSet();

            ad.Fill(ds);

            return ds;

        }

    }

}

using System;

using System.Collections.Generic;

using System.Text;

using System.Data;

using BaiThi.DungChung;

namespace BaiThi.Thaotacbang

{

    class tblLop

    {

        string maLop, tenLop, khoa;

        int namvao;

        public string MaLop

        {

            set { maLop = value; }

            get { return maLop; }

        }

           public string TenLop

        {

            set { tenLop = value; }

            get {return tenLop;  }

        }

           public string Khoa

        {

            set { khoa = value; }

            get {return khoa ; }

        }

           public int Namvao

        {

            set { namvao = value; }

            get { return namvao; }

        }

        public void Them()

        {

            string sql = string.Format("insert into Lop values('{0}','{1}',{2},'{3}')", MaLop, TenLop, Namvao, Khoa);

            thaotacdb.ThucHien(sql);

        }

        public void sua()

        {

            string sql = string.Format("update Lop set TenLop ='{0}',namvao = {1},Khoa='{2}' where MaLop = '{3}'", TenLop, Namvao, Khoa, MaLop);

            thaotacdb.ThucHien(sql);

        }

        public static void xoa(string malop)

        {

            string sql = string .Format ("delete from lop where malop = '{0}'",malop );

            thaotacdb.ThucHien(sql);

        }

        public static List<tblLop> LayDSLop(string DK)

        {

            string sql = string.Format("select * from lop where {0}", DK);

            DataSet ds = thaotacdb.LayDataset(sql);

            List<tblLop> lst = new List<tblLop>();

            foreach (DataRow  r in ds.Tables [0].Rows )

            {

                tblLop t = new tblLop();

                t.MaLop = r["MaLop"].ToString();

                t.TenLop = r["TenLop"].ToString();

                t.Namvao =int.Parse ( r["Namvao"].ToString());

                t.Khoa = r["Khoa"].ToString();

                lst.Add(t);

            }

            return lst;

        }

        public static tblLop LayTTLop(string MaLop)

        {

            string sql = string.Format("select * from Lop where MaLop ='{0}'", MaLop);

            DataSet ds = thaotacdb.LayDataset(sql);

            if (ds.Tables[0].Rows.Count >0)

            {

                tblLop t = new tblLop();

                t.MaLop = ds.Tables[0].Rows[0]["MaLop"].ToString();

                t.TenLop = ds.Tables[0].Rows[0]["TenLop"].ToString();

                t.Namvao = int.Parse(ds.Tables[0].Rows[0]["Namvao"].ToString());

                t.Khoa = ds.Tables[0].Rows[0]["Khoa"].ToString();

                return t;

            }

            else

                return null;

        }

    }

}

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using BaiThi.Thaotacbang;

namespace BaiThi

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)

        {         

            List<tblLop> lst = tblLop.LayDSLop("1=1");

            gridLop.DataSource = lst;

        }

        private void Them_Click(object sender, EventArgs e)

        {

            double tmp;

            if (txtMaLop.Text == "" || txtTenLop.Text == "" || txtKhoa.Text == "" || double.TryParse(txtNamVao.Text, out  tmp) == false)

            {

                MessageBox.Show("Du lieu nhap vao ko dung");

                return;

            }

            if (tblLop.LayTTLop(txtMaLop .Text ) != null  )

            {

                MessageBox.Show("Du lieu TRUNG");

                return;

            }

            tblLop t = new tblLop();

            t.MaLop = txtMaLop.Text;

            t.TenLop = txtTenLop.Text;

            t.Namvao = int.Parse(txtNamVao.Text);

            t.Khoa = txtKhoa.Text;

            t.Them();

            MessageBox.Show("Da Them");

            List<tblLop> lst = tblLop.LayDSLop("1=1");

            gridLop.DataSource = lst;

        }

        private void gridLop_Click(object sender, EventArgs e)

        {

            string MaLop = gridLop.CurrentRow.Cells["MaLop"].Value.ToString();

            tblLop t = tblLop.LayTTLop(MaLop);

            txtMaLop.Text = t.MaLop;

            txtTenLop.Text = t.TenLop;

            txtNamVao.Text = t.Namvao.ToString();

            txtKhoa .Text = t.Khoa ;

        }

        private void Sua_Click(object sender, EventArgs e)

        {

            tblLop t = new tblLop();

            t.MaLop = txtMaLop.Text;

            t.TenLop = txtTenLop.Text;

            t.Namvao = int.Parse(txtNamVao.Text);

            t.Khoa = txtKhoa.Text;

            t.sua();

            MessageBox.Show("Da sua");

            List<tblLop> lst = tblLop.LayDSLop("1=1");

            gridLop.DataSource = lst;

        }

        private void Xoa_Click(object sender, EventArgs e)

        {

            string malop = gridLop.CurrentRow.Cells["MaLop"].Value.ToString();

            tblLop.xoa(malop);

            MessageBox.Show("Da Xoa");

            List<tblLop> lst = tblLop.LayDSLop("1=1");

            gridLop.DataSource = lst;

        }

        private void thoat_Click(object sender, EventArgs e)

        {

            Close();

        }

        private void nhaplai_Click(object sender, EventArgs e)

        {

            txtMaLop.Text = "";

            txtTenLop.Text = "";

            txtNamVao.Text = "";

            txtKhoa.Text = "";

        }

    }

}