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);
            }
        }
    }
}