private OleDbConnection conn;

    private OleDbCommand cmd;

    public studentDA()

    {

        conn = new DBconnection().conn;

        cmd = conn.CreateCommand();

    }

    public List<studentdata> select()

    {

        List<studentdata> list = null;

        cmd.CommandText = "select *from student";

        conn.Open();

        OleDbDataReader dr = cmd.ExecuteReader();

        if(dr.HasRows)

            list = new List<studentdata>();

        while (dr.Read())

        {

            studentdata data = new studentdata();

            data.Code = (int)dr["code"];

            data.Nam = dr["Nam"].ToString();

            data.Sex = dr["Sex"].ToString();

            data.Tizhong = decimal.Parse(dr["Tizhong"].ToString());

            data.Age = int.Parse(dr["Age"].ToString());

            data.Yuwen = decimal.Parse(dr["Yuwen"].ToString());

            data.Shuxue = decimal.Parse(dr["Shuxue"].ToString());

            data.Yingyu = decimal.Parse(dr["Yingyu"].ToString());

            data.Banji = dr["Banji"].ToString();

            list.Add(data);

        }

        conn.Close();

        return list;

    }

public OleDbConnection conn;

    public DBconnection()

    {

        conn = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source="+HttpContext.Current.Server.MapPath("~/App_Data/mydb.accdb"));

    }