namespace LinqInNotIn
{
    internal class Program
    {
        static void Main(string[] args)
        {
            List<Product> products = new List<Product>();
            products.Add(new Product(1, "Scissors"));
            products.Add(new Product(2, "Pencil"));
            products.Add(new Product(3, "Ballpen"));
            //products.Add(new Product(3, "Null Ballpen"));
            products.Add(new Product(4, "Snack"));
            products.Add(new Product(5, "Beverage"));

            int[] ids = { 2, 4, 5 };
            
            var inQuery = from item in products
                        where ids.Contains(item.ProductId)
                        select item;

            var notInQuery = from item in products
                             where !ids.Contains(item.ProductId)
                             select item;

            Console.WriteLine("inQuery");
            foreach (var item in inQuery)
            {
                Console.WriteLine($"idx: {item.ProductId}, name: {item.Name}");
            }

            Console.WriteLine("notInQuery");
            foreach (var item in notInQuery)
            {
                Console.WriteLine($"idx: {item.ProductId}, name: {item.Name}");
            }

            Console.WriteLine("first, single");
            var firstItem = products.First(item => item.ProductId == 3);
            var singleItem = products.Single(item => item.ProductId == 3);
            Console.WriteLine($"first == single: {firstItem == singleItem}");
        }
    }
}