possible null reference return c# linq

Question

I have this linq query. It complains with the warning message.

Warning CS8603: Possible null reference return

Code:

return await _applicationDbContext.Pies
                .Include(x => x.Portions).AsSingleQuery()
                .Include(x => x.Ingredients).AsSplitQuery()
                .SingleOrDefaultAsync(x => x.Id == id);

Further more this is making it ugly with squiggles all over.

Can anything be done about it?

Looked at the following SO posts, but could not figure out what to do.

What do you want your method to return if there is 0 or more than 1 pies? — TVOHM
– TVOHM, Commented Dec 29, 2021 at 11:33
It is not just a case of changing the method to return Task<Pie?>? — ProgrammingLlama
– ProgrammingLlama, Commented Dec 29, 2021 at 11:34

sommmen · Accepted Answer · 2023-01-23 11:10:55Z

7

SingleOrDefaultAsync() does exactly what's in the method name, it tries to find a single entry and returns the default if nothing is found.

The default for a reference type, your object Pie in this case, is null hence the warning.

You can either return Task<Pie?> or instead handle the null value in some way. One way would be to use .SingleAsync() instead, which will throw if nothing was found - but therefore it will never return null.

edited Jan 23, 2023 at 11:10

answered Dec 29, 2021 at 11:34

sommmen

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DaveShaw · Accepted Answer · 2021-12-29 11:35:13Z

5

The method returns a Task<Pie>.

The return ... has SingleOrDefaultAsync(...) at the end which means if it cannot find an item with a matching id it will return default(Pie) which will be null.

You need to decide if either:

This method can return null, then change the signature to Task<Pie?> to let calling code know that it can return null.
This method shouldn't return null, use SingleAsync(...) so that it will throw a runtime exception if no matching id is found.

answered Dec 29, 2021 at 11:35

DaveShaw

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