object custom property

   Hi guys,

I need to sum related objects values to a custom property of parent object to use as a display property in a datagrid source.

The equivalent SQL query would look like:

SELECT     RR.RentReviewID, 
                 RR.ReviewDate, 
                 SUM(RRI.IncomeValue) AS TotalIncome
FROM         RentReview RR JOIN
                  RentReviewIncome RRI ON RR.RentReviewId = RRI.RentReviewId
GROUP BY  RR.RentReviewId,
                  RR.ReviewDate

RentReview object has RentReviewIncome as associated object.

The query I currently execute is:-

var query = Manager.RentReviews
                .Where(a => a.Tenancy.tenancyID == tenancyID)
                .OrderByDescending(a => a.effectiveFromDate)
                .Include("Schedule")
                .Include("RentReviewIncomes");

Query(query, callback);

This returns associated RentReviewIncome objects, but where to from there?

I was hoping something like this custom property on the RentReview object might do the trick, but no.
public decimal TotalIncome { get { return (decimal)RentReviewIncomes.Sum(incomeValue); } }