JavaScript Object Notation - JSON

namespace ProductShop
{
    using System.IO;
    using Newtonsoft.Json;
    using ProductShop.Data;
    using ProductShop.Models;
    using System.Collections.Generic;
    using System.Linq;
    using System;
    using ProductShop.Dtos.Export;
    using Newtonsoft.Json.Serialization;

    public class StartUp
    {
        private const string ImportMessage = "Successfully imported {0}";

        public static void Main(string[] args)
        {
            var context = new ProductShopContext();

            // 04. Import Categories and Products
            var categoriesProductsJason = File.ReadAllText(@"C:\Users\Nik\Desktop\Product Shop\ProductShop\Datasets\categories-products.json");
            Console.WriteLine(ImportCategoryProducts(context, categoriesProductsJason));
        }

        // 04. Import Categories and Products
        public static string ImportCategoryProducts(ProductShopContext context, string inputJson)
        {
            //var validCategoruIds = context
            //    .Categories
            //    .Select(c => c.Id)
            //    .ToHashSet();

            var validCategoryIds = new HashSet<int>(
                context
                    .Categories
                    .Select(c => c.Id));

            var validProductIds = new HashSet<int>(
                context
                    .Products
                    .Select(p => p.Id));

            var categoriesProducts = JsonConvert.DeserializeObject<CategoryProduct[]>(inputJson);
            var validEntities = new List<CategoryProduct>();

            foreach (var categoryProduct in categoriesProducts)
            {
                bool isValid = validCategoryIds.Contains(categoryProduct.CategoryId) &&
                               validProductIds.Contains(categoryProduct.ProductId);

                if (isValid)
                {
                    validEntities.Add(categoryProduct);
                }
            }

            context.CategoryProducts.AddRange(validEntities);
            context.SaveChanges();

            return string.Format(ImportMessage, validEntities.Count);
        }
    }
}