C# asynch SQL inside singleton and delegates

Question

I\'m trying to build a class that will be responsible for all operations on database.

Using singleton pattern from here: http://codebender.denniland.com/a-singleton-base

Answer 1

public delegate void NotifyCallback(string message);    

public class ClassWithCommandAndCallback 
{
  public SqlCommand Sql;
  public NotifyCallback Callback;
}

public void loadData(NotifyCallback callback)
{
  ClassWithCommandAndCallback ar = new ClassWithCommandAndCallback();
  ar.Sql = cmd;
  ar.Callback = callback;
  IAsyncResult result = cmd.BeginExecuteReader(new AsyncCallback(HandleCallback), ar, CommandBehavior.CloseConnection);
}

private void HandleCallback(IAsyncResult result)
{
  ClassWithCommandAndCallback ar = (ClassWithCommandAndCallback)result.AsyncState;

  ar.Callback("loaded (SQL was: "+ar.Sql+")");
}