[LRUG] Rails - The Missing Parts

[Simon Coffey]

On 3 March 2014 20:38, Tom Blomfield <tomblomfield at gmail.com> wrote:
>
> I wrote a blog post on Interactors in Rails -
> http://eng.joingrouper.com/blog/2014/03/03/rails-the-missing-parts-interactors

Nice article, thanks for sharing!

To play devil's advocate, though: despite using them myself, I'm a bit
unsure about service objects/interactors/use cases.

We've got a fair few of them in our main app for things like user
registration and so forth. While they've cleaned up our controllers
somewhat, get a modest amount of reuse and are manifestly superior to
AR lifecycle callbacks, I can never escape the feeling that they're
still a bit of a junk drawer. ("Yeah, but what have you done for me
*lately*?")

Misgivings:

* non-SRP: creating DB records, sending emails, firing background jobs
* corollary: they tend to have a whole bunch of dependencies
* corollorollary: testing them is still a pain (even with DI)
* what actually *is* a UserRegistrationService instance[1]?
* why do I have a whole class with a single public "run" method?

It often feels like they're little more than high-ceremony functions.
With Interactors there's a bit of success/failure state being
maintained, but it doesn't seem to do anything that raising exceptions
wouldn't (less, really, if you've got to handle multiple failure
modes).

We've extracted genuine cross-cutting concerns into a pub-sub event
system[2], so things like email delivery are properly isolated, but
there's still a gunky residue, which is why we've still got service
objects.

So what is that residue? In our codebase it's often things that would
live in a model constructor if Rails allowed you to define
constructors for your models. But the pattern isn't consistent enough
that I can just say, "okay, this gunk compensates for Rails," which
makes me feel like service objects are still a failure of design
somehow, but I can't put my finger on what's missing.

Anyone else share these doubts, or am I just making up problems for myself?

Cheers,
Simon

[1] A ranty version of this objection:
http://me.veekun.com/blog/2013/03/03/the-controller-pattern-is-awful-and-other-oo-heresy/
[2] atrocious blogspam, sorry:
http://techblog.tribesports.com/blog/2012/08/21/pub-sub-system-events-for-post-action-tasks/