using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var received = new List<Foo>{new Foo{ProductId=1,WarehouseSectionId=2}};

        var reserved = new List<Foo>{};

        var leftOuterJoin = from r in received

                    join rs in reserved

                    on new {a = r.ProductId, b = r.WarehouseSectionId } equals new { a = rs.ProductId, b =  rs.WarehouseSectionId } into joinedL

                    from rs in joinedL.DefaultIfEmpty()

                    select r;

        Console.WriteLine(leftOuterJoin.First().ProductId);

    }

}

class Foo

{

    public int ProductId;

    public int WarehouseSectionId;

}