How to make oledb query asychronous - c#-5.0

Question

I'm having problems with this query, it takes a long time to run and is timing out. I wanted to try to make it async but I can't find a good example that's close to what I'm trying to do.
Below is what I've tried, it starts but does nothing. This is inside a WinForm project.
namespace access_db_csharp
{
public partial class Form1 : Form
{
string SQL = "";
public Form1()
{
InitializeComponent();
textBox1.Text = "Select Project, Request, Release, TestName, AssignmentNumber, Formulation, Container, Closure FROM tblWtLossBottDropResults";
textBox2.Text = "Where Container LIKE '%2700-305%'";
dataGridView1.Focus();
}
OleDbConnection con=new OleDbConnection ();
OleDbCommand cmd=new OleDbCommand ();
string connectionstring = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=K:\R&D Dept\Development Lab\DLab Databases and Add Ins\DLab Results Database\DLab Results Individual Tables.accdb;Jet OLEDB:Database Password='roscoe'";
private async void button1_Click(object sender, EventArgs e)
{
Task<DataTable> task = new Task<DataTable>(RunQuery);
task.Start();
}
private DataTable RunQuery()
{
if (checkBox1.Checked == true)
{
SQL = textBox1.Text + " " + textBox2.Text;
}
else
{
SQL = textBox1.Text;
}
OleDbConnection con = new OleDbConnection(connectionstring);
OleDbCommand cmd = new OleDbCommand(SQL, con);
con.Open();
cmd.CommandType = CommandType.Text;
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
DataTable tblWtLossBottDropResults = new DataTable();
da.Fill(tblWtLossBottDropResults);
dataGridView1.DataSource = tblWtLossBottDropResults;
//dataGridView1.ColumnCount = 17;
dataGridView1.Columns[0].Name = "Project";
dataGridView1.Columns[1].Name = "Request";
dataGridView1.Columns[2].Name = "Release";
dataGridView1.Columns[3].Name = "TestName";
dataGridView1.Columns[4].Name = "AssignmentNumber";
dataGridView1.Columns[5].Name = "Formulation";
dataGridView1.Columns[6].Name = "Container";
dataGridView1.Columns[7].Name = "Closure";
MessageBox.Show("Done");
int numRows = dataGridView1.RowCount;
label4.Text = "Rows Returned: " + numRows.ToString();
return tblWtLossBottDropResults;
}
private void Form1_Load(object sender, EventArgs e)
{
con.ConnectionString = connectionstring;
con.Open();
}
}
}
Ideally I want to get the data from the query and load it into a datagridview table.

Answer 1

There are a few things you should change:
1. You should not mix UI and non-UI code.
2. You should keep your connection open for the shortest amount of time.
Because the OleDb provider doesn't have asynchronous APIs, your database code will be synchronous:
private DataTable RunQuery(string commandText)
{
using (var connection = new OleDbConnection(connectionstring))
{
using (var command = connection.CreateCommand())
{
command.CommandType = CommandType.Text;
command.CommandText = commandText;
using (var dataAdapter = new OleDbDataAdapter(command))
{
connection.Open();
var dataTable = new DataTable();
dataAdapter.Fill(dataTable);
return dataTable;
}
}
}
}
Because it's a Windows Forms application you can use Task.Run to offload that work to the thread pool and free the UI thread:
private async void button1_Click(object sender, EventArgs e)
{
var commandText = checkBox1.Checked
? textBox1.Text + " " + textBox2.Text
: textBox1.Text;
var dataTable = await Task.Run(() => RunQuery(commandText));
/* This should be set on the designer or on the constructor
//dataGridView1.ColumnCount = 17;
dataGridView1.Columns[0].Name = "Project";
dataGridView1.Columns[1].Name = "Request";
dataGridView1.Columns[2].Name = "Release";
dataGridView1.Columns[3].Name = "TestName";
dataGridView1.Columns[4].Name = "AssignmentNumber";
dataGridView1.Columns[5].Name = "Formulation";
dataGridView1.Columns[6].Name = "Container";
dataGridView1.Columns[7].Name = "Closure";
*/
dataGridView1.DataSource = dataTable;
MessageBox.Show("Done");
int numRows = dataGridView1.RowCount;
label4.Text = "Rows Returned: " + numRows.ToString();
}