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Discussion on: Why null in C# is so bad

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donut87 profile image
Christian Baer

Please do not return null because your query did not find anything.
Null is the absence of information. It's the abbreviation for "I don't know what happened". Please don't put meaning to it. Do not return null in any case. Throw exceptions, return error objects or whatever, but do not return null. Null is contains zero information and has no meaning.

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peledzohar profile image
Zohar Peled • Edited

I would never suggest throwing an exception if something wasn't found in the database. that's an entirely non-exceptional situation and throwing an exception because of that would be, IMHO, a perfect example of a vexing exception.
(Even if you store information in a database that is needed for the software to run, such as configuration information - even in this case, I would rather handling the lack of critical information in code, rather then throwing an exception).

Also, Null in c# (like Nothing in Vb.Net) is not "the absence of information" - it's a reference that doesn't point to an instance. What you are referring to might be Null in the world of relational databases, where it is most accurately described as an unknown value.

To me, having a method returning null when data wasn't found makes perfect sense - because the data was not found, an instance of the return type could not have been initialized, and therefor you get back null.

This can be replaced by using something like the Maybe Monad (click here for a long but good explanation), but IMHO that's a more complicated solution to the same problem.
I mean, you'd have to check if the Maybe is none or if it contains a value anyway, so you might as well check if the reference is null - with no extra complication to your codebase.

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donut87 profile image
Christian Baer

A Reference that points to nothing is the absence of information. There is literally nothing (read: no information) behind the pointer.
For a database query neither null/Null nor an exception are the right tool. An empty List would be. If you query for exactly one Object (like with the id), null/Null can be an option. So could an Exception, as if you have an ID, there better be an object for this. This depends on the context.
Problem is: Null/null returns are also often misused. It is still dangerous and clutters code. For me it is a 'Do not use lightly'. I have to have a reason for using something so dangerous.

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peledzohar profile image
Zohar Peled

True, if you're selecting a list of object, an empty list (or an IEnumerable) would be the obvious choice of what to return when you find nothing that matches the search criteria. For a search of a single object, I see no problem with null. I guess we can simply agree to disagree.