AsyncPages in ASP.NET 2.0

I'd like a review of this implementation of Async in ASP.NET 2.0 web form page below. Let me know if I am missing something.

AsyncPagesASPNET20.aspx

AsyncPagesASPNET20.aspx.cs

public partial class AsyncPagesASPNET20 : System.Web.UI.Page
{
    private string queryCustomerSelect = "SELECT FirstName, LastName FROM SalesLT.Customer";
    private DataAccess dataAccess = new DataAccess(WebConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            this.PreRenderComplete += AsyncPage_PreRenderComplete;
            AddOnPreRenderCompleteAsync(new BeginEventHandler(BeginAsyncOperation), new EndEventHandler(EndAsyncOperation));
        }
    }

    private void EndAsyncOperation(IAsyncResult ar)
    {
        Trace.Write("EndAsyncOperation...");
        this.dataAccess.EndAsyncSelect(ar);
    }

    private IAsyncResult BeginAsyncOperation(object sender, EventArgs e, AsyncCallback cb, object extraData)
    {
        Trace.Write("BeginAsyncOperation...");
        return dataAccess.BeginAsyncSelect(sender, e, cb, extraData, this.queryCustomerSelect);
    }

    void AsyncPage_PreRenderComplete(object sender, EventArgs e)
    {
        this.GridView1.DataSource = this.dataAccess.reader;
        this.GridView1.DataBind();
    }

    public override void Dispose()
    {       
        this.dataAccess.Dispose();
    }
}

DataAccess.cs

```
public class DataAccess : IDisposable
{
string connectionString = string.Empty;
private SqlConnection connection;
private SqlCommand command;
public SqlDataReader reader;
public DataAccess(string connectionString)
{
this.connectionString = connectionString;
this.connection = new SqlConnection(this.connectionString);
this.command = new SqlCommand();
}

public IAsyncResult BeginAsyncSelect(object sender, EventArgs e, AsyncCallback cb, object ext

Overall a very cleanly written class. It is easy to follow and understand.

A couple of suggestions though.

Make the reader class variable a Property with a private setter. This will eliminate the ability to reassign it from outside of the class. I would also rename it Reader to fit with C# coding standards.

Most C# coding standards I have read suggest prefixing private class variables with a _. This will allow you to remove the this. statement whenever you need to access one of the class variables. I think doing that will make you code much easier to read.

I'm not sure what the SelectSync method is used for. I see it as a way to do a non-async query into the database. If that is the case, I would move it to a different class as it interferes with the async nature of the one you have written. Maybe rename this class to DataAccessAsync, and have a second one DataAccess? Its hard to say without an example of a call to that method.

I can't see much more at this point.

StackExchange Code Review Q#15287, answer score: 2