Where to handle duplicate key exceptions in multy layer application

Question

+-------------+         +--------+        +----------+
| repository  +-------->+service +------->+controller|
+-------------+         +-^------+        +------------+
+-------------+           |  +^  ++------>+controller2 |
| repository2 +-----------+  |    |       +------------+
+-------------+              |    +------>+controller3 |
+------------+               |            +------------+
| repository3+---------------+
+------------+

I want to be able to support multiple different implementations of my repository interface. I use my interface in by business service and I can select what ever implementation I want. So far so good.

When I try to insert multiple entries with the same key, db connector will throw an exception. In case of jdbcTemplate, this will be DuplicateKeyException, in case of Hibernate, this will likely be some kind of Constraint Exception. Not ideal, but still good enough.

I must be able to tell the service consumer what exactly went wrong any why, where passing the exception is not good enaugh (as in response 500). Getting muddy.

So my options are either to catch that exception in the controller, which then I have to implement in each controller (which seems muddy waters to me), or, I can throw some kind of exception in the business service (which seems better) and then handle that in the controller. I think this is better because then I'll be catching my own one of a kind exception, and I'm sure what's going on.

The problem is, most of my business service implementation is actually an existing interface implementation, which means that in order to do this, I have to override the interface I'm using with new declarations which will have exceptions. This is not what I want.

What is the proper way to handle this kind of situation? I'm using Spring but I would like a more general answer.

Answer 1

Interfaces

Aren't just about method signatures. They are also about the exceptions that can be thrown across them.

So the simple answer is that each of your repositories needs to catch their own exceptions,and then translate them into an acceptable exception to throw across the interface.

The controllers will then need to catch the translated exceptions, and because the translated exceptions will follow one convention, they need only catch a (for example) DuplicateKeyException and then respond indicating the error that occurred. So if its a simple language response, plain English (or whatever the human speaks). If its a semantic error, hopefully there is a code for Duplicate Key.