public async Task <bool> DeleteAsync(int id)
        {
            var customer = await _context.StudentInfos.SingleOrDefaultAsync(c => c.Id == id);

            _context.Remove(customer);
            try
            {
                return(await _context.SaveChangesAsync() > 0 ? true : false);
            }
            catch (System.Exception exp)
            {
            }
            return(false);
        }