static void AddProduct(string categoryName, string productName, double price) { using var shoppingContext = new ShoppingContext(); var category = shoppingContext.Category.Where(x => x.Name == categoryName).FirstOrDefault(); var product = new Product { Name = productName, Price = price, Categories = new List <ProductCategory>() { new ProductCategory() { Category = category } } }; shoppingContext.Products.Add(product); shoppingContext.SaveChanges(); }