public async Task <IActionResult> Submit([FromBody] AssignmentViewModel model)
        {
            if (ModelState.IsValid)
            {
                var assignment = await _assignmentRepository.GetById(model.Id);

                var answer = model.Answer;

                // assignment of Extra Round
                if (assignment.Extra)
                {
                    answer = $"{model.Answer}. Standnummer van exposant: {model.Question.Exhibitor.ExhibitorNumber}," +
                             $"Exposantnaam: {model.Question.Exhibitor.Name}";
                }
                else // assignment of normal tour
                {
                    var question = await _questionRepository.GetById(assignment.Question.Id);

                    var exhibitor = await _exhibitorRepository.GetById(question.CategoryExhibitor.ExhibitorId);

                    exhibitor.GroupsAtExhibitor--;
                }

                assignment.Answer = answer;
                assignment.Notes  = model.Notes;
                if (!String.IsNullOrEmpty(model.Photo))
                {
                    assignment.Photo = _imageWriter.WriteBase64ToFile(model.Photo);
                }
                assignment.Submitted = true;
                await _assignmentRepository.SaveChanges();

//                if (result.Succeeded)
                //TODO: temporary, recursive loop anders:
                assignment = await _assignmentRepository.GetByIdLight(assignment.Id);

                return(Ok(assignment));
            }

            return(Ok(
                       new
            {
                Message = "Error, the submitted assignment is not valid."
            }));
        }