รบกวนช่วยดูทีนะคะ ไม่สามารถโชว์ข้อมูลผ่านทาง DataGridVIew ได้ค่ะ (MS Access+VB C# )

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

namespace OneTime
{
    public partial class FormSaleOrder : Form
    {
        public FormSaleOrder()
        {
            InitializeComponent();
        }


        private DataSet _dataset;
        private OleDbConnection _conn;
        private OleDbCommand _cmd;
        private OleDbDataAdapter _adapter;



        private void FormSaleOrder_Load(object sender, EventArgs e)
        {
            string conStr = "Provider=Microsoft.Ace.OleDb.12.0;" 
                + @"Data Source=C:\Onetime Database\Database.accdb";

            _conn = new OleDbConnection(conStr);
            _conn.Open();

            string sql = "SELECT * FROM Customer";
            _cmd = new OleDbCommand(sql, _conn);
            OleDbDataReader reader = _cmd.ExecuteReader();

            while(reader.Read())
                cbxCust.Items.Add(reader["CustomerName"]);

            sql = "SELECT * FROM Product";
            _cmd = new OleDbCommand(sql, _conn);
            reader = _cmd.ExecuteReader();


            while (reader.Read())
                cbxProduct.Items.Add(reader["ProductName"]);

            dateTimePicker1.Value = DateTime.Today;

            cbxCust.SelectedIndex = 0;
            cbxProduct.SelectedIndex = 0;
            btnDelete.Enabled = false;

           
        }

        private void FormSaleOrder_FormClosing(object sender, FormClosingEventArgs e)
        {
            _conn.Close();
        }


        private void showOrder()
        {
            string sql = "SELECT * FROM SaleOrder WHERE CustomerName = @cust";

            _cmd = new OleDbCommand(sql, _conn);
            _cmd.Parameters.AddWithValue("cust", cbxCust.SelectedItem);

            _adapter = new OleDbDataAdapter(_cmd);
            _dataset = new DataSet();

            _adapter.Fill(_dataset, "order");

            dataGridView1.DataSource = _dataset.Tables["order"];
        }

        private void cbxCust_SelectedIndexChanged(object sender, EventArgs e)
        {
            showOrder();
        }

        private void btnAdd_Click(object sender, EventArgs e)
        {
            double quan;
            if (!double.TryParse(txbTotal.Text, out quan))
            {
                MessageBox.Show("จำนวนไม่ถูกต้อง");
                return;
            }


            string sql = "INSERT INTO SaleOrder(CustomerName, ProductName, Quantity, OrderDate) VALUE (@cust, @product, @quan, @orderdate)";

            _cmd = new OleDbCommand(sql, _conn);
        
            _cmd.Parameters.AddWithValue("cust", cbxCust.SelectedItem);
            _cmd.Parameters.AddWithValue("product", cbxProduct.SelectedItem);
            _cmd.Parameters.AddWithValue("quan", quan);
            _cmd.Parameters.AddWithValue("orderdate", dateTimePicker1.Value);

            int affectedRow = _cmd.ExecuteNonQuery();
            if (affectedRow < 1)

                MessageBox.Show("Error!");
            else
                showOrder();

        }

        private void dataGridView1_RowStateChanged(object sender, DataGridViewRowStateChangedEventArgs e)
        {
            if (dataGridView1.SelectedRows.Count > 0)
                btnDelete.Enabled = true;
            else
                btnDelete.Enabled = false;
        }

        
       



      
    }
}