public async Task OnPost()
        {
            try
            {
                var vm = new ConcertViewModel()
                {
                    BandName = BandName,
                    Capacity = Capacity,
                    Name     = Name
                };

                await _controller.AddConcert(vm);
            }
            catch (Exception ex)
            {
                IsError      = true;
                ErrorMessage = ex.Message;
                throw;
            }
        }