Linq to SQL空值检查计算

Question

I have function which calculates quantity .Its working fine but some due to null values in field it does not return anything . these field can be null .i want to calculate only where both fields are not null. i think i need to use foreach but i dont know the way how can i use it here . Help appreciated

 private double Get_Quantity() 
    {
        try
        {
            double sum = 0;

            sum = (double)(from s in ManagerClass.oSqlData.table
                           where s.Demand.Order.Order_ID == Order_ID 
                           where s.Demand.Order.Order_Date >= ManagerClass.startDate && s.Demand.Order.Order_Date <= ManagerClass.EndDate

                           select s.ValueA - s.ValueB ).Sum();
            return sum;
        }
        catch
        {
            return 0;
        }
    }

Answer 1

Try like this;

        sum = (double)(from s in ManagerClass.oSqlData.table
            where (s.Demand != null && s.Demand.Order != null && s.Demand.Order.Order_ID == Order_ID)
            && (s.Demand != null && s.Demand.Order != null && s.Demand.Order.Order_Date >= ManagerClass.startDate && s.Demand.Order.Order_Date <= ManagerClass.EndDate)
                  && s.ValueA != null
                  && s.ValueB != null
            select s.ValueA - s.ValueB).DefaultIfEmpty(0).Sum();