public IActionResult CreateCategory(CategoryCreationData request)
        {
            int categories = _context.Categories
                             .Count(c => c.Label == request.Label);

            if (categories > 0)
            {
                return(BadRequest(new
                {
                    message = "Šiuo pavadinimu kategorija jau egzistuoja."
                }));
            }

            _context.Categories.Add(new Category
            {
                Label    = request.Label,
                ParentId = request.ParentId
            });

            _context.SaveChanges();
            return(Ok(new
            {
                message = "Nauja kategorija sukurta."
            }));
        }
        public IActionResult ModifyCategory(int id, CategoryCreationData request)
        {
            if (!ModelState.IsValid)
            {
                return(BadRequest(ModelState));
            }

            Category modifying = _context
                                 .Categories.SingleOrDefault(c => c.Id == id);

            if (modifying != null)
            {
                modifying.Label    = request.Label;
                modifying.ParentId = request.ParentId == 0 || request.ParentId == null ? null : request.ParentId;
                _context.SaveChanges();
                return(Ok());
            }

            return(BadRequest());
        }