Linq error when using let

Question

I have the following linq query and it is giving the following error: A query body must end with a select clause or a group clause

from sdc in ScheduleDestinationCaches
let twins = from gt in GetTwins(72)
join ssFilter in ScheduleStops on sdc.CarrierID equals ssFilter.CarrierID
join ssLookup in ScheduleStops on sdc.CityID equals ssLookup.CityID
join sc in ScheduleCarriers on ssLookup.CarrierID equals sc.CarrierID
where twins.Contains(ssFilter.StopID ) || ssFilter.StopID == 72
select sc

any ideas?

By the way I'm using linqpad

from MSDN: http://msdn.microsoft.com/en-us/library/bb383976.aspx it looks like you're missing a second `from` clause after the `let` cause. Yes I realize it's for C# syntax, but in this case, it's basically identical except the semicolon at the end. — user2366842, Aug 15 '14 at 16:50
It is complaining about `from gt in GetTwins(72)` which doesn't have a select. — sgmoore, Aug 15 '14 at 16:50

MarcinJuraszek · Accepted Answer · 2014-08-15T17:27:31.813

Let's add some indentation:

from sdc in ScheduleDestinationCaches
let twins = from gt in GetTwins(72)
            join ssFilter in ScheduleStops on sdc.CarrierID equals ssFilter.CarrierID
            join ssLookup in ScheduleStops on sdc.CityID equals ssLookup.CityID
            join sc in ScheduleCarriers on ssLookup.CarrierID equals sc.CarrierID
            where twins.Contains(ssFilter.StopID ) || ssFilter.StopID == 72
            select sc

Can you see the issue now? Adding from as an assignment to let-defined variable starts new LINQ expression, which end with select sc. This makes the outer query not to have select clause at all!

I think you're looking for

from sdc in ScheduleDestinationCaches
let twins = GetTwins(72)
join ssFilter in ScheduleStops on sdc.CarrierID equals ssFilter.CarrierID
join ssLookup in ScheduleStops on sdc.CityID equals ssLookup.CityID
join sc in ScheduleCarriers on ssLookup.CarrierID equals sc.CarrierID
where twins.Contains(ssFilter.StopID ) || ssFilter.StopID == 72
select sc

Comments-based update

from sdc in ScheduleDestinationCaches
let twins = GetTwins(72).Select(x => x.Id)
join ssFilter in ScheduleStops on sdc.CarrierID equals ssFilter.CarrierID
join ssLookup in ScheduleStops on sdc.CityID equals ssLookup.CityID
join sc in ScheduleCarriers on ssLookup.CarrierID equals sc.CarrierID
where twins.Contains(ssFilter.StopID ) || ssFilter.StopID == 72
select sc

Thank you. I can see and understand the difference. Now I'm getting a different error: 'System.Linq.IQueryable' does not contain a definition for 'Contains' and the best extension method overload 'System.Linq.ParallelEnumerable.Contains(System.Linq.ParallelQuery, TSource)' has some invalid arguments Instance argument: cannot convert from 'System.Linq.IQueryable' to 'System.Linq.ParallelQuery' — user1286550, Aug 15 '14 at 17:09
That's because `GetTwins` returns a collection of objects, and you're trying to check if it contains an `int` value. That will not work. — MarcinJuraszek, Aug 15 '14 at 17:23
Add `Select(x => x.Id)` (or whatever the property name is) call after `GetTwins`. — MarcinJuraszek, Aug 15 '14 at 17:27

Linq error when using let

1 Answers1