Не сохраняются данные в базе после изменений, сделанных в datagridview. Помогите, пожалуйста

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Data.OleDb;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Windows.Forms;

namespace newnewnew
{
class Form1 : Form
{


DataGridView dg;
OleDbDataAdapter da;
DataTable dt;
DataSet ds;
public Form1()


{
this.Width = 700;
this.Height = 700;

this.Text = "Двустороннее связывание";

string sql = "select * from Склад_Аксесуары";
string connectionstring;

connectionstring = "Provider=Microsoft.Jet.OLEDB.4.0;" + @"Data Source =d:\vitaly.mdb";
OleDbConnection conection = new OleDbConnection(connectionstring);
conection.Open();



Button btnSave = new Button();
btnSave.Text = "Save";
btnSave.Click += new System.EventHandler(BtnSave_Click);
btnSave.Location = new Point(200, 10);
btnSave.Width = 100;
this.Controls.Add(btnSave);



dg = new DataGridView();
dg.Width = 500;
dg.Height = 400;
dg.Location = new Point(50,50);
dg.AutoResizeColumns();
this.Controls.Add(dg);




da = new OleDbDataAdapter();

OleDbCommand command;
command = new OleDbCommand(sql, conection);
da.SelectCommand = command;
command = new OleDbCommand("UPDATE Склад_Аксесуары set Аксесуары=?", conection);
da.UpdateCommand = command;

dt = new DataTable();
ds = new DataSet();

da.Fill(dt);


dg.DataSource = dt;

}

static void Main()
{

Application.Run(new Form1());
}

private void BtnSave_Click(object sender, System.EventArgs e)
{

da.Update(dt);
//da.Update((DataTable)dg.DataSource);
MessageBox.Show
("Получилочь!!!!!");
}
}
}