Using Linq to determine the missing combination of records - linq

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)