C＃Windows应用程序访问数据库数据不会在关闭时持续存在

我正在使用C＃创建Windows应用程序，由此访问了一个空的Access数据库，该数据库包含两个表：Provinces和Locations。我正在处理只处理Provinces表的表单，如下所示：

这是一个子窗体。当它打开时，我可以插入/更新记录等。每当进行更改时，我都单击“加载表”按钮以在DataGridView对象中显示更改。

如果关闭此子窗体并再次显示它，则可以单击“加载表”按钮，然后调出所有数据以显示在DataGridView对象中。但是，如果我完全关闭该应用程序，那么我将丢失所有数据。我通过双击数据库文件以在Access中启动它来证明这一点，在那里我可以看到数据肯定消失了。因为我不知道为什么数据不能持久保存在文件中，所以这已经成为一个谜。请指教。

下面是表格的代码。您可以从我的方法中看到，每次执行函数时，我都会关闭连接对象。所以我茫然为什么我在应用程序关闭时总是丢失数据？

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

namespace GTI_Taxi_Pricing
{
public partial class frmProv : Form
{
    private OleDbConnection connection = new OleDbConnection();
    public frmProv()
    {
        InitializeComponent();
        connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=TaxiDB.accdb;Persist Security Info=False;";                
    }

    private void btnLoad_Click(object sender, EventArgs e)
    {
        try
        {
            connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            String query = "SELECT * FROM Provinces;";
            command.CommandText = query;
            OleDbDataAdapter da = new OleDbDataAdapter(command);
            DataTable dt = new DataTable();
            da.Fill(dt);
            dataGridView1.DataSource = dt;
            connection.Close();
        }
        catch(Exception ex)
        {
            MessageBox.Show("Error: " + ex);
        }
    }

    private void btnSave_Click(object sender, EventArgs e)
    {
        if (txtName.Text == "")
        {
            MessageBox.Show("The name field must have a value.");
            return;
        }
        try
        {
            connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            command.CommandText = "INSERT INTO Provinces (name) VALUES ('" + txtName.Text + "')";

            command.ExecuteNonQuery();
            MessageBox.Show("Data Saved");
            connection.Close();
        }
        catch(Exception ex)
        {
            MessageBox.Show("Error: " + ex);
        }
    }

    private void btnNewRecord_Click(object sender, EventArgs e)
    {
        txtID.Text = "";
        txtName.Text = "";
    }

    private void btnEdit_Click(object sender, EventArgs e)
    {
        if (txtID.Text == "")
        {
            MessageBox.Show("The id field must have a value.");
            return;
        }
        if(txtName.Text == "")
        {
            MessageBox.Show("The name field must have a value.");
            return;
        }
        try
        {
            connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            command.CommandText = "UPDATE Provinces SET name='" + txtName.Text + "' WHERE id=" + txtID.Text + ";";

            command.ExecuteNonQuery();
            MessageBox.Show("Data Update Successful.");
            connection.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error: " + ex);
        }
    }

    private void btnDelete_Click(object sender, EventArgs e)
    {
        if (txtID.Text == "")
        {
            MessageBox.Show("The id field must have a value.");
            return;
        }
        try
        {
            connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            command.CommandText = "DELETE FROM Provinces WHERE id=" + txtID.Text + ";";

            command.ExecuteNonQuery();
            MessageBox.Show("Record Deleted Successfully.");
            connection.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error: " + ex);
        }
    }

    private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
    {
        if(e.RowIndex >= 0)
        {
            DataGridViewRow row = dataGridView1.Rows[e.RowIndex];
            txtID.Text = row.Cells[0].Value.ToString();
            txtName.Text = row.Cells[1].Value.ToString();
        }
    }
}

}