How to read null for null-able Boolean values

Question

I am trying to read nullable values from a database. Right now my code is converting null values to false. How can I modify my code to allow for null values?

Ap1ExamTaken = dr["AP1_ExamTaken"] != DBNull.Value && Convert.ToBoolean(dr["AP1_ExamTaken"]),

I would like values that are null to be shown as null and not false.

You say you want to show the value but in the code snippet I cannot see anything, that shows it. There's just an assignment. — sticky bit, May 01 '19 at 14:51
Basically if the db value is null I want Ap1ExamTaken to equal null other wise it'll equal true/false. — smuldr, May 01 '19 at 14:52
@JeroenMostert: Is that assuming that `dr` is a `DataRow`? I'd been assuming `SqlDataReader` or similar. — Jon Skeet, May 01 '19 at 14:54
@JonSkeet: It is indeed; force of habit of seeing this exact kind of code many, many times. (More so than for a data reader, in any case.) — Jeroen Mostert, May 01 '19 at 14:56

Jon Skeet · Accepted Answer · 2019-05-01T14:59:27.373

You could use the conditional operator here, to set it to null if the value is DBNull.Value, or a non-nullable value otherwise:

Ap1ExamTaken = dr["AP1_ExamTaken"] == DBNull.Value ? null : (bool?) dr["AP1_ExamTaken"];

Note that this will throw an exception if dr["AP1_ExamTaken"] is a non-boolean, non-DBNull type, which I suspect is what you want.

You could write it more compactly as:

Ap1ExamTaken = dr["AP1_ExamTaken"] as bool?

... but then you'll end up with a null value if the value is some other type (a string, an integer etc) which I'd generally be alarmed about. (If my data doesn't have the shape I expect, I want to know ASAP.)

How to read null for null-able Boolean values

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