Can't set nullable int to LINQ query's return value?

Question

I want to retrieve an Id from a table based on certain criteria. If the criteria isn't met, I just want to return the default value (in this case, I'm assuming null). Here's my code:

int? circuitTypeId = cimsContext.CircuitTypes.FirstOrDefault(ct => ct.Name == circuitType).Id;

I am assuming that if there isn't a match between ct.Name and circuitType that the value returned is null. However, when running my program, I get an error on this line saying "Null reference exception". I know that the record isn't there, but shouldn't I be able to assign the null returned by the query to my nullable int variable?

No, at the moment you'll need to explicitly check for null before dereferencing Id. Or you can wait for [Roslyn's Elvis](http://stackoverflow.com/q/27493541/314291) operator `?.` :) — StuartLC, Jan 05 '15 at 05:37
`FirstOrDefault` is worthless in this situation because you're trying to access `Id` from potentially `null`. `First` would at least throw a better exception. — jamesSampica, Jan 05 '15 at 05:38

score 5 · Answer 1 · answered Jan 05 '15 at 05:42

Your assumption is wrong, as per your query:-

int? circuitTypeId = cimsContext.CircuitTypes
                                .FirstOrDefault(ct => ct.Name == circuitType).Id;

This will return int, when match is found but it will throw a Null Reference Exception when no name matches with that of circuitType. you should do this:-

var circuitTypeObj = cimsContext.CircuitTypes
                                .FirstOrDefault(ct => ct.Name == circuitType);
int? circuitTypeId = circuitTypeObj == null ? (int?)null : circuitTypeObj.Id;

Amol Bavannavar · Answer 2 · 2015-01-05T05:47:04.937

3

Try this :

int? circuitTypeId = cimsContext.CircuitTypes.Where(ct => ct.Name == circuitType).Select(p => p.Id).FirstOrDefault();

edited Jan 05 '15 at 05:47

answered Jan 05 '15 at 05:41

Amol Bavannavar

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This should be the accepted answer ;-) short and clean without unnecessary `if`s. – t3chb0t Jan 05 '15 at 07:08
8

Nope. This will return a `0` instead of a `null`. – Carter Medlin May 08 '17 at 21:10

score 3 · Answer 3 · answered May 08 '17 at 21:24

3

In C# version 6 you can simply add a ? before id to prevent the properties of null objects from being referenced.

int? circuitTypeId = cimsContext.CircuitTypes.FirstOrDefault(ct => ct.Name == circuitType)?.Id;

answered May 08 '17 at 21:24

Carter Medlin

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score 2 · Accepted Answer · answered Jan 05 '15 at 05:38

2

You should first check for null before assigning the circuitTypeId variable:

int? circuitTypeId;

var circuitType = cimsContext.CircuitTypes.FirstOrDefault(ct => ct.Name == circuitType);
if(circuitType != null)
{
    circuitTypeId = circuitType.Id;
}

answered Jan 05 '15 at 05:38

dotnetom

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score 1 · Answer 5 · answered Jan 05 '15 at 05:39

The problem is .Id is probably trying to reference a null CirctuitType.

var circuitType = cimsContext.CircuitTypes.FirstOrDefault(ct => ct.Name == circuitType);
int? circuitTypeId = circuitType.Id; // if circuitType is null, a null reference exception is thrown

Instead, you'll need to test the reference for null:

var circuitType = cimsContext.CircuitTypes.FirstOrDefault(ct => ct.Name == circuitType);
int? circuitTypeId = (circuitType == null ? (int?)null : circuitType.Id);

Can't set nullable int to LINQ query's return value?

5 Answers5