Which .NET exception to throw for invalid database state?

Question

I am writing some data access code and I want to check for potentially "invalid" data states in the database. For instance, I am returning a widget out of the database and I only expect one. If I get two, I want to throw an exception. Even though referential integrity should prevent this from occurring, I do not want to depend on the DBAs never changing the schema (to clarify this, if the primary key constraint is removed and I get a dupe, I want to break quickly and clearly).

I would like to use the System.IO.InvalidDataException, except that I am not dealing with a file stream so it would be misleading. I ended up going with a generic applicationexception. Anyone have a better idea?

Answer 1

InvalidDataException seems pretty reasonable to me:

• The name fits perfectly
• The description fits pretty reasonably when you consider that it's effectively a data "stream" from the database
• Nothing in the description mentions files, so I wouldn't be worried about that side of things

You're effectively deserializing data from a store. It happens to be an RDBMS, but that's relatively unimportant. The data is invalid, so InvalidDataException fits well.

To put it another way - if you were loading the data from a file, would you use InvalidDataException? Assuming you would, why should it matter where the data is coming from, in terms of the exception being thrown?