Question

Let me start to explain with an example.

var vProducts = new[] {
    new { Product = "A", Location ="Y", Month = "January", Demand = 50 },
    new { Product = "A", Location ="Y", Month = "February", Demand = 100 },
    new { Product = "A", Location ="Y", Month = "March", Demand = 20 },
    new { Product = "A", Location ="Y", Month = "June", Demand = 10 }
};

var vPeriods = new[] {
    new { Priority = 1, Month = "January" },
    new { Priority  = 2, Month = "February" },
    new { Priority  = 3, Month = "March" },
    new { Priority  = 4, Month = "April" },
    new { Priority  = 5, Month = "May" },
    new { Priority  = 6, Month = "June" }
};

var vAll = from p in vProducts
       from t in vPeriods
       select new
           {
             Product = p.Product,
             Location = p.Location,
             Period = t.Priority,
             PeriodName = t.Month,
             Demand = p.Demand
           };

This above query will create all combinations of Products & Period. But, I need to get a list of all products along with the ones that do not have matching Month as shown below.

example

Product      Location      Priority        Month    Demand
  A              Y            1           January     50
  A              Y            2          February    100
  A              Y            3           March       20
  A              Y            4           April       null
  A              Y            5           May         null
  A              Y            6           June        10

Thanks for any comments.

Answer 1

You want to do a left outer join, it will go something like:

var res = from period in vPeriods
                  join product in vProducts on period.Month equals product.Month into bla
                  from p in bla.DefaultIfEmpty()
                  select new { period.Month, period.Priority, Product = p == null ? null : p.Product, Demand = p == null ? -1 : p.Demand };

  foreach (var a in res)
            {
                Console.WriteLine(string.Format("{0} {1} {2}", a.Product, a.Month, a.Demand));
            }

Of course that products that do not have matching months don’t have locations etc. (as you stated in your example)