C
C#•4w ago
DaClownie

Accessing the value contained within a record struct

I have a record struct of AssessmentResponse: 
public record struct AssessmentResponse
    (
        Guid Id,
        string Name,
        int Type,
        DateTime DateStart,
        DateTime DateEnd
    );
public record struct AssessmentResponse
    (
        Guid Id,
        string Name,
        int Type,
        DateTime DateStart,
        DateTime DateEnd
    );
I understand this is an immutable object, in that once its been created it can't be modified... but how do I get access to the Id of this DTO for use in my code? 
[Parameter]
public AssessmentResponse? ParentAssessment { get; set; }

Guid assessmentId = ParentAssessment.Id;
[Parameter]
public AssessmentResponse? ParentAssessment { get; set; }

Guid assessmentId = ParentAssessment.Id;
obviously the last line doesn't work but I'm not trying to modify the record struct, I just want access to the data. I'm passing the AssessmentResponse? if it exists to the Blazor component, and want to access the Id section for the API call to update the record in my database. My AssessmentService.Update call requires an Guid, AssessmentRequest I guess alternatively I could modify the AssessmentRequest to have an Id property contained within it and allow it to be nullable? but there's got to be a way to access the Id within the record struct and assign its value to another variable for use elsewhere.
5 Replies
SleepWellPupper
SleepWellPupper•4w ago
AssessmentResponse? is syntactic sugar for Nullable<AssessmentResponse> See here on how to work with nullable value types (structs); specifically, to get the value from a Nullable<AssessmentResponse>, you would have to go through the .Value property;i.e.: ParentAssessment.Value.Id. Do note that you should check if ParentAssessment is null before accessing Value. https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-value-types
Nullable value types - C# reference
Learn about C# nullable value types and how to use them
DaClownie
DaClownieOP•4w ago
ohhhh, I kept trying to do that but in the wrong order. I was using ParentAssessment.Id.Value. Let me give that a try. I'm catching the null in another spot and shortened it to just show what i was having an issue with Give me a few and I'll report back Fantastic, that was it I'll read up more on that link you sent. Thanks! Also, that .HasValue feels like it would be a lot cleaner than always doing if (Id is not null) or some variation of that
SleepWellPupper
SleepWellPupper•4w ago
You could also do if(nullableVariable is {} variable); that will extract the underlying value and you can then use it in the body of the if statement: var id = variable.Id;
DaClownie
DaClownieOP•4w ago
Is it essentially creating a copy of it? so 
if(ParentAssessment is {} assessment);
var assessmentId = assessment.Id;
if(ParentAssessment is {} assessment);
var assessmentId = assessment.Id;
? At that point, I wouldn't need to make another copy of it to assessmentId, I could just use assessment.Id as I see fit?
SleepWellPupper
SleepWellPupper•4w ago
// ParentAssessment is of type Nullable<AssessmentResponse>
if(ParentAssessment is { } assessment)
{
  // assessment is of type AssessmentResponse
  var assessmentId = assessment.Id;
  // do stuff with id or assessment
}
// assessment is assigned to here; you can't use it outside the if statement block
// ParentAssessment is of type Nullable<AssessmentResponse>
if(ParentAssessment is { } assessment)
{
  // assessment is of type AssessmentResponse
  var assessmentId = assessment.Id;
  // do stuff with id or assessment
}
// assessment is assigned to here; you can't use it outside the if statement block
yes but your if condition in your code ends at the semicolon; that wouldn't compile Ah there might be some confusion, in my previous message "You could also do if(nullableVariable is {} variable)", the semicolon was not part of the sample code :)

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