Null Warnings Re: Student, Course Create and Edit

Question

Working on the following Contoso University Tutorial...

https://learn.microsoft.com/en-us/aspnet/core/data/ef-mvc/crud?view=aspnetcore-6.0#update-the-edit-page

The code runs successfully but has some warnings...

Errors:

Warning (active) CS8602 Dereference of a possibly null reference.

Severity Code Description Project File Line Suppression State

Warning CS8620 Argument of type 'IIncludableQueryable<Student, ICollection<Enrollment>?>' cannot be used for parameter 'source' of type 'IIncludableQueryable<Student, IEnumerable<Enrollment>>' in 'IIncludableQueryable<Student, Course?> EntityFrameworkQueryableExtensions.ThenInclude<Student, Enrollment, Course?>(IIncludableQueryable<Student, IEnumerable<Enrollment>> source, Expression<Func<Enrollment, Course?>> navigationPropertyPath)' due to differences in the nullability of reference types. ContosoUniversity C:\Users\User1\Desktop_Tech\Net_Contoso University_ContosoUniversity\ContosoUniversity\Controllers\StudentController.cs 38 Active

Project on GitHub:

https://github.com/DeanEverhart/ContosoUniversity1

Answer 1

Hi @Dean Everhart

These messages are warnings instead of errors, Your code and work well with these warnings. Here is the explanation from Microsoft Document:

• CS8602 - Dereference of a possibly null reference.
• CS8620 - Argument cannot be used for parameter due to differences in the nullability of reference types.

From descriptions you can see it is all about nullable in asp.net core, You can also refer to this Docs to learn more about Working with Nullable Reference Types.

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