Question

I use the following code in wcf ria services (Silverlight App):

 public partial class BillingWaterDomainService : LinqToEntitiesDomainService<BilingWaterEntities>
    {
        public ObservableCollection<PaymentSummary> GetPaymentSummary(long requestId)
        {
            var paymentSummaries = new ObservableCollection<PaymentSummary>();

            var result = GetRequestCostDetailsByRequestId(requestId);
            foreach (var requestCostDetail in result.Where(r=>r.BranchCostId.HasValue))
            {
                if (requestCostDetail.Debtor.HasValue)
                {
                    RequestCostDetail detail = requestCostDetail;

                    long? costCustomerPrice = 0;                       
                    costCustomerPrice =
                        result.Where(
                            r => r.CostCustomerDetail.CostCustomerType.CostTypeId == detail.BranchCostDetail.CostType && r.Creditor.HasValue).
                            Sum(r => r.Creditor != null ? r.Creditor.Value : 0);

                    paymentSummaries.Add(new PaymentSummary()
                                             {
                                                 PaymentTitle = requestCostDetail.BranchCostDetail.CostType1.CostTitle,
                                                 Price = requestCostDetail.Debtor.Value-(costCustomerPrice.HasValue ? costCustomerPrice.Value:0)
                                             });
                }
            }


            return paymentSummaries;
        }
    }

When i try execute this code, i have following error:

Invoke Operation
‘GetPaymentSummary’ failed.The cast to value type ‘Int64’ failed
because the materialized value is null.Either the result type ‘s
generic parameter or the query must use a nullable type

this error in the following line of code:

costCustomerPrice =result.Where(
                            r => r.CostCustomerDetail.CostCustomerType.CostTypeId == detail.BranchCostDetail.CostType && r.Creditor.HasValue).
                            Sum(r => r.Creditor != null ? r.Creditor.Value : 0);

And This piece of code:

r => r.CostCustomerDetail.CostCustomerType.CostTypeId

how can i solve this problem?!

Answer 1

It seems that r => r.CostCustomerDetail.CostCustomerType.CostTypeId is null for some entries. Try adding a condition:

results.Where(r => r.CostCustomerDetail.CostCustomerType.CostTypeId.HasValue)
    .Where(... 

Or maybe even r.CostCustomerDetail.CostCustomerType is sometimes null.

You can also do this:

... .Select(r => r.Creditor != null ? r.Creditor.Value : 0)
       .DefaultIfEmpty(0).Sum()