webform连接ACCESS数据库

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"));

    }