linq

PacticeSolution/LinqInNotIn/LinqInNotIn.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

PacticeSolution/LinqInNotIn/Product.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LinqInNotIn
+{
+    internal class Product
+    {
+        public int ProductId { get; set; }
+        public string Name { get; set; }
+
+        public Product(int id, string name)
+        {
+            this.ProductId = id;
+            this.Name = name;
+        }
+    }
+}

PacticeSolution/LinqInNotIn/Program.cs

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