public async Task <ActionResult <Category> > PostCategory(Category category)
        {
            if (category.Id != 0)
            {
                return(null);
            }
            string c = _context.PostCategory(category);

            if (c == "Category added successfully.")
            {
                _context.db_categories.Add(category);
                await _context.SaveChangesAsync();

                return(CreatedAtAction("GetCategory", new { id = category.Id }, category));
            }
            else
            {
                return(null);
            }
        }