Exception when using LINQ SUM

Question

I'm trying to get the SUM of "bookings" and I get error "The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type."

var bookings = entities.Bookings.Where(x => x.ID == id &&
                                     x.StartDate <= bookingEnd &&
                                     x.EndDate >= bookingStart)
                                    .Sum(x => x.BookingQuantity);

How shall I fix this? I need to get 0 if it ever gets to be null else its bookings.

Same question here: stackoverflow.com/questions/2076827/…

VikciaR
– VikciaR

2011-04-15 10:18:46 +00:00
Commented Apr 15, 2011 at 10:18 — VikciaR
– VikciaR, Commented Apr 15, 2011 at 10:18

Simon Gill · Accepted Answer · 2011-04-15 10:02:07Z

41

Try the null coalescing operator:

var bookings = entities.Bookings.Where(x => x.ID == id &&
                                 x.StartDate <= bookingEnd &&
                                 x.EndDate >= bookingStart && 
                                 x.BookingQuantity != null)
                                .Sum(x => (int?)x.BookingQuantity) ?? 0;

or declare bookings as a nullable int

int? bookings = ...

The compilers type inference is picking up the result of Sum as a plain int, which should never be null.

answered Apr 15, 2011 at 10:02

Simon Gill

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1 Comment

Zapnologica Over a year ago

In my case it also returns int, not nullable int which doesn't make sense. How does the ?? 0 fix it then?

Chris McAtackney · Accepted Answer · 2011-04-15 10:01:25Z

15

This page suggests a fix to this problem;

Sum(x => (int?)x.BookingQuantity) ?? 0;

answered Apr 15, 2011 at 10:01

Chris McAtackney

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2 Comments

Zapnologica Over a year ago

my compiler throws an error saying '?? cannot be applied to type int'

Chris McAtackney Over a year ago

Did you cast it to (int?) ?

VikciaR · Accepted Answer · 2011-04-15 09:56:43Z

1

Add checking for null.

var bookings = entities.Bookings.Where(x => x.ID == id &&
                                     x.StartDate <= bookingEnd &&
                                     x.EndDate >= bookingStart && 
                                     x.BookingQuantity != null)
                                    .Sum(x => x.BookingQuantity);

answered Apr 15, 2011 at 9:56

VikciaR

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1 Comment

Lasse Edsvik Over a year ago

SELECT * FROM Bookings WHERE BookingQuantity IS NULL returns 0 rows, so all have 1 or more if there are any.

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