public IHttpActionResult Create(CategoryViewModel category)
        {
            if (!this.ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var newCategory = new Category
            {
                Name = category.Name,
            };

            this.data.Categories.Add(newCategory);
            this.data.Categories.SaveChanges();

            category.Id = newCategory.Id;
            return Ok(newCategory);
        }
        public IHttpActionResult Update(int id, CategoryViewModel category)
        {
            if (!this.ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var existingCategory = this.data.Categories.Find(id);
            if (existingCategory == null)
            {
                return BadRequest(CategoryNotFoundExceptionMassage + "category.");
            }

            existingCategory.Name = category.Name;
            this.data.Categories.SaveChanges();

            category.Id = existingCategory.Id;
            return Ok(existingCategory);
        }