Linq101-Join

 using System;
 using System.Collections.Generic;
 using System.Linq;

 namespace Linq101
 {
     internal class Join
     {
         /// <summary>
         /// This sample shows how to efficiently join elements of two sequences based on equality between key expressions over the two.
         /// </summary>
         public void Linq102()
         {
             string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
             List<Data.Product> products = Data.GetProductList();

             var q = from c in categories
                     join p in products on c equals p.Category
                     select new { Category = c, p.ProductName };

             ObjectDumper.Write(q);
         }

         /// <summary>
         /// Using a group join you can get all the products that match a given category bundled as a sequence.
         /// </summary>
         public void Linq103()
         {
             string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
             List<Data.Product> products = Data.GetProductList();

             var q = from c in categories
                     join p in products on c equals p.Category into ps
                     select new { Category = c, Products = ps };

             foreach (var v in q)
             {
                 Console.WriteLine(v.Category + ":");
                 foreach (var p in v.Products)
                 {
                     Console.WriteLine("   " + p.ProductName);
                 }
             }
         }

         /// <summary>
         /// The group join operator is more general than join, as this slightly more verbose version of the cross join sample shows.
         /// </summary>
         public void Linq104()
         {
             string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
             List<Data.Product> products = Data.GetProductList();

             var q = from c in categories
                     join p in products on c equals p.Category into ps
                     from p in ps
                     select new { Category = c, p.ProductName };

             foreach (var v in q)
             {
                 Console.WriteLine(v.ProductName + ": " + v.Category);
             }
         }

         /// <summary>
         /// A so-called outer join can be expressed with a group join. A left outer joinis like a cross join,
         /// except that all the left hand side elements get included at least once, even if they don't match any right hand side elements.
         /// Note how Vegetablesshows up in the output even though it has no matching products.
         /// </summary>
         public void Linq105()
         {
             string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
             List<Data.Product> products = Data.GetProductList();

             var q = from c in categories
                     join p in products on c equals p.Category into ps
                     from p in ps.DefaultIfEmpty()
                     select new { Category = c, ProductName = p == null ? "(No Products)" : p.ProductName };

             foreach (var v in q)
             {
                 Console.WriteLine(v.ProductName + ": " + v.Category);
             }
         }
     }
 }