Question

Whats wrong with the below query, I am getting this error:
Nullable object must have a value.

  Dim subscriptionUsers = From inv In dataContext.Invoices.ToList Join u In dataContext.Users _
                                    On inv.Subscription Equals u.Subscription _
                                    Where inv.Id.Value = invoiceID _
                                    And Not u.Fund.Title.Contains("AGM") _
                                    And DirectCast(IIf(Not u.EndDate.HasValue, IIf(u.StartDate.Value <= inv.EndDate.Value, True, False), _
                                                    IIf((u.StartDate.Value >= inv.StartDate.Value And u.StartDate.Value <= inv.EndDate.Value) Or _
                                                (u.EndDate.Value >= inv.StartDate.Value And u.EndDate.Value <= inv.EndDate.Value) Or _
                                                (u.StartDate.Value < inv.StartDate.Value And u.EndDate.Value > inv.EndDate.Value), True, False)), Boolean) _
                                Group By Key = u.Fund.Title Into Group _
                                Select Fund = Key, UsersCount = Group.Count, Users = Group.ToList, _
                                SubFunds = (From a In dataContext.Allocations Where a.Fund.Title = Key Select a.Department.Title Distinct)

If I remove the u.EndDate.Value in the condition then it works fine.

Here is the stack trace:

at System.Nullable1.get_Value()
at SDBReports.InvoiceAllocationReportUserControl._Lambda$__4(VB$AnonymousType_02 $VB$It)
at System.Linq.Enumerable.WhereEnumerableIterator1.MoveNext()
at System.Linq.Lookup2.Create[TSource](IEnumerable1 source, Func2 keySelector, Func2 elementSelector, IEqualityComparer1 comparer)
at System.Linq.GroupedEnumerable4.GetEnumerator()
at System.Linq.Enumerable.WhereSelectEnumerableIterator2.MoveNext()
at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

p.s. I have used SPMetal to generate the entity classes on SharePoint lists.

For more clarity:

do not get confused with u.EndDate.Value and inv.EndDate.Value

here is the true part for u.EndDate.Hasvalue:

 IIf((u.StartDate.Value >= inv.StartDate.Value And u.StartDate.Value <= inv.EndDate.Value) Or _
                                                (u.EndDate.Value >= inv.StartDate.Value And u.EndDate.Value <= inv.EndDate.Value) Or _
                                                (u.StartDate.Value < inv.StartDate.Value And u.EndDate.Value > inv.EndDate.Value), True, False)

and here is the false part

IIf(u.StartDate.Value <= inv.EndDate.Value, True, False)

Answer 1

• Use If instead of IIf. This is short-circuited (like C#’s conditional operator) and will work because the conditions are only evaluated if HasValue is True. IIf is deprecated. Never use it.

• Furthermore, an expression like If(condition, True, False) is nonsensical. Replace it with just condition.

• Finally, you need to use AndAlso instead of And – once again, for short-circuiting to happen. In fact, always use AndAlso and OrElse in conditionals. Use And and Or only when doing bit operations.

• The DirectCast is also unnecessary.

This leaves us with a much simplified expression:

If(Not u.EndDate.HasValue, u.StartDate.Value <= inv.EndDate.Value), _
    (u.StartDate.Value >= inv.StartDate.Value AndAlso u.StartDate.Value <= inv.EndDate.Value) OrElse _
    (u.EndDate.Value >= inv.StartDate.Value AndAlso u.EndDate.Value <= inv.EndDate.Value) OrElse _
    (u.StartDate.Value < inv.StartDate.Value AndAlso u.EndDate.Value > inv.EndDate.Value))

But this expression is still much too complex. You should split this up but first assigning the values inside the nullables to some temporary variable using Let inside the query.