public IActionResult GetCategoryById(int categoryId)
        {
            var category = _categoryRepository.GetCategoryById(categoryId);

            if (category == null)
            {
                ModelState.AddModelError("", "Error getting a category");
                ViewBag.Message = $"There was a problem retrieving category with id {categoryId} " +
                                  $"From the database or no category with that id exists";
                category = new CategoryDto();
            }

            var books = _categoryRepository.GetAllBooksForCategory(categoryId);

            if (books.Count() <= 0)
            {
                ViewBag.BookMessage = $"{category.Name} has no books";
            }

            var bookCategoryViewModel = new CategoryBooksViewModel()
            {
                Category = category,
                Books    = books
            };

            // because of create / update / delete method so we have to have it
            ViewBag.SuccessMessage = TempData["SuccessMessage"];
            return(View(bookCategoryViewModel));
        }
        public IActionResult GetCategoryById(int categoryId)
        {
            var category = _categoryRepository.GetCategoryById(categoryId);

            if (category == null)
            {
                ModelState.AddModelError("", $"There is no category with id:{categoryId}");
                ViewBag.Message = $"There was a problem retrieving category with id {categoryId} " +
                                  $"from the database or no category exists";
                category = new CategoryDto();
            }

            var books = _categoryRepository.GetAllBooksForCategory(categoryId);

            if (books.Count() <= 0)
            {
                ViewBag.BookMessage = $"Category: {category.Name} has no books";
            }

            var bookCategoryViewModel = new CategoryBooksViewModel()
            {
                Category = category,
                Books    = books
            };


            return(View(bookCategoryViewModel));
        }