When to use custom exceptions vs. existing exceptions vs. generic exceptions

Question

I\'m trying to figure out what the correct form of exceptions to throw would be for a library I am writing. One example of what I need to handle is logging a user in to a st

Answer 1

You have two species of exceptions.

Those that are specific to your application, where it's good to avoid any existing exceptions.

Your application-specific exceptions should simplify the use cases for the folks who use your libraries. 3 of your application specific exceptions are things users can do. The fourth (badge does not exist) is clearly not procedural, but far more serious.

It looks like you have two application-specific errors: user-oriented things and administrative mistakes.

The others are part of some other piece of technology; i.e., database errors. You can -- generally -- ignore these. If the DB isn't available, the API will throw errors and you can let those bubble up through your library.

You can also "wrap" these as an application-specific exception which contains a lower-level exception. This is sometimes helpful if there is a lot of lower-level technology. In your case, it's just a database. Ignore it and let the DB errors bubble through.