What are the best practices for catching and re-throwing exceptions?

Question

Should caught exceptions be re-thrown directly, or should they be wrapped around a new exception?

That is, should I do this:

try {
  $connect = new C         


        

Answer 1

Well, it's all about maintaining the abstraction. So I'd suggest using exception chaining to throw directly. As far as why, let me explain the concept of leaky abstractions

Let's say you're building a model. The model is supposed to abstract away all of the data persistence and validation from the rest of the application. So now what happens when you get a database error? If you rethrow the DatabaseQueryException, you're leaking the abstraction. To understand why, think about the abstraction for a second. You don't care how the model stores the data, just that it does. Likewise you don't care exactly what went wrong in the underlying systems of the model, just that you know that something went wrong, and approximately what went wrong.

So by rethrowing the DatabaseQueryException, you're leaking the abstraction and requiring the calling code to understand the semantics of what's going on under the model. Instead, create a generic ModelStorageException, and wrap the caught DatabaseQueryException inside of that. That way, your calling code can still try to deal with the error semantically, but it doesn't matter the underlying technology of the Model since you're only exposing errors from that abstraction layer. Even better, since you wrapped the exception, if it bubbles all the way up and needs to be logged, you can trace to the root exception thrown (walk the chain) so you still have all the debugging information that you need!

Don't simply catch and rethrow the same exception unless you need to do some post-processing. But a block like } catch (Exception $e) { throw $e; } is pointless. But you can re-wrap the exceptions for some significant abstraction gain.