Linq WhereListIterator issue

Question

Linq WhereListIterator issue

AS 211

My code is

AreaTimePlan[LocationPlanLoop - 1].AllocatedLocation = (Location)(from newLoc in Global.Locations where newLoc.ToLocations.First()== Flight.Origin && newLoc.Type.Title == AreaTimePlan[LocationPlanLoop - 1].LocationType.Title select newLoc).First();

Global.Locations is a list of Location objects
Flight.Origin is a single Location object
NewLoc.ToLocations is a list of Location objects

I get a runtime error - Unable to cast object of type 'WhereListIterator`1[Airport_Server.Location]' to type 'Airport_Server.Location'.'

My intention is that AreaTimePlan[LocationPlanLoop - 1].AllocatedLocation contains a Location which has a ToLocation equal to Origin.

Firstly I'm not sure if I need to use a cast or re-write my Linq query? Secondly whichever I need to use I would appreciate help on the correct implementation.

Thanks

Karen Payne MVP 35,591 Reputation points Volunteer Moderator

2021-01-12T19:27:52.05+00:00

Rather than creating a long LINQ statement, break it apart and diagnose the results to learn where the issue is. As it's currently written it's not going to be easy to diagnose the problem which after you figure it out keep it that way or go back to a one liner although a one liner currently is really the issue.
AS 211 Reputation points

2021-01-12T21:42:07.313+00:00

Thanks for your advice.

Apologises, I think my original issue was a testing error as I'm now not getting an error from the code. I'm still testing. I'll post an updated comment or answer when I've done more testing. I thought I'd tested correctly before posting but it seems not.
Ken Tucker 5,861 Reputation points

2021-01-13T09:41:14.503+00:00
I would change newLoc.ToLocations.First() to a variable so it does not have to keep doing the .First() inside the linq loop

where newLoc.ToLocations.First()
AS 211 Reputation points

2021-01-13T16:12:25.753+00:00

Thank you for the advice.

In the long term I intend to work out how to improve the statement so that it returns a list of any newLoc location which has a 'ToLocation' that matches flight.origin.

Using .First() was because then it's a single location and can then be compared to Flight.Origin. A workaround so I can continue with other parts of the code and come back to this issue.

Answer accepted by question author

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Karen Payne MVP 35,591 Reputation points Volunteer Moderator

2021-01-12T19:27:52.05+00:00

Rather than creating a long LINQ statement, break it apart and diagnose the results to learn where the issue is. As it's currently written it's not going to be easy to diagnose the problem which after you figure it out keep it that way or go back to a one liner although a one liner currently is really the issue.
AS 211 Reputation points

2021-01-12T21:42:07.313+00:00

Thanks for your advice.

Apologises, I think my original issue was a testing error as I'm now not getting an error from the code. I'm still testing. I'll post an updated comment or answer when I've done more testing. I thought I'd tested correctly before posting but it seems not.
Ken Tucker 5,861 Reputation points

2021-01-13T09:41:14.503+00:00

I would change newLoc.ToLocations.First() to a variable so it does not have to keep doing the .First() inside the linq loop

where newLoc.ToLocations.First()
AS 211 Reputation points

2021-01-13T16:12:25.753+00:00

Thank you for the advice.

In the long term I intend to work out how to improve the statement so that it returns a list of any newLoc location which has a 'ToLocation' that matches flight.origin.

Using .First() was because then it's a single location and can then be compared to Flight.Origin. A workaround so I can continue with other parts of the code and come back to this issue.

Answer 1

Timon Yang-MSFT 9,606

@AS
Did you really call First() during testing?
The problem seems to be caused by not calling this method.

AS 211 Reputation points

2021-01-13T15:59:17.15+00:00

Thanks for your help.

That was exactly the issue. I tried First() as my last test and thought I tested before posting but I must have made a mistake. If you convert your comment to an answer then I will mark it as accepted.

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Linq WhereListIterator issue

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