public void Purge()
        {
            using (ExpenseDataContext ctx = new ExpenseDataContext())
            {
                List<Expense> resultList =
                    (from expense in ctx.Expenses
                     select expense).ToList();

                foreach (Expense expense in resultList)
                {
                    ctx.DeleteObject(expense);
                }

                ctx.SaveChanges();
            }
        }