public IActionResult AddProduct(CategoryAndProductsViewModel modelData)
        {
            Association newAssociation = modelData.NewAssociation;

            dbContext.Add(newAssociation);
            dbContext.SaveChanges();
            return(RedirectToAction("CategoryPage", new { categoryid = newAssociation.CategoryId }));
        }
        public IActionResult CategoryPage(int categoryid)
        {
            CategoryAndProductsViewModel ViewModel = new CategoryAndProductsViewModel()
            {
                TheCategory           = dbContext.Categories.Where(c => c.CategoryId == categoryid).Include(c => c.Products).ThenInclude(c => c.Product).FirstOrDefault(),
                NonassociatedProducts = dbContext.Products.Where(p => p.Categories.All(c => c.CategoryId != categoryid)).ToList()
            };

            return(View(ViewModel));
        }