I've been playing with the Ruby community's interactor pattern and found a few issues.
The Ruby and Rails communities often use a gem (package) called interactor which aims to make logic encapsulated into self-contained pieces. After writing a few interactors myself, I came across a few problems that I thought I’d share.
Interactors are often used to wrap code that will receive an input, and return an output. Here’s an example that takes some input (
name) and returns output (
The way interactors handle this is by using a
context object that holds both inputs and outputs. I’ve found that having one object hold both inputs and outputs gets messy very quickly.
Interactors provide an
Organizer class which allows breaking apart interactors into smaller, reusable interactors. However, doing so often means the concept of “inputs” and “outputs” are a bit blurred.
RegisterUser class can be refactored into 3 sub-interactors. At this point, the inputs and outputs start to get difficult to make sense of.
I’ve found that the more organisers are used, the more
context becomes harder to manage. One way to keep track of this is making some graph that keeps track of these things. (These tables can get quite difficult to manage very quickly.)
Interactors are often touted for being useful for managing reusable pieces of logic. Here’s one example of business logic that might be useful in many places.
context.email input, and throws an error if it's not valid.
While this logic is nicely self-contained, it’s not easily reusable in an organizer that might take in a different input shape.
context.params.email, not the
context.email expected by ValidateEmail. In this case, ValidateEmail can't be re-used as-is.
Nested interactors break error handling. Because Interactor Organisers enforce the use of the same
context fields, it’s often better to call interactors directly from other interactors.
call! stop the execution when an error is encountered. However, it doesn't work that way...
Unfortunately, the code above wouldn’t work, because errors are swallowed by default even when using
call!. The fix here is to intentionally rescue Interactor errors and re-raise them using
rescue block will be needed when using
call! inside interactors. See the discussion on GitHub.
Here are a few ideas I had on how to work around these limitations with interactors.
Organisers impose strict restrictions on how code is supposed to be structured, and I feel that the restrictions don’t necessarily make for better code. It’s not worth the extra effort in my opinion, and nested interactors are a more reasonable alternative.
Gems like dry.rb allows writing runtime validation for types. Static compile-time type checking is most ideal in my opinion (eg, Ruby type signatures or Sorbet), but runtime validation is the closest alternative.
Many devs I talked to who uses interactors have written some code to fix the shortcomings of
fail! errors being swallowed. This snippet might be good to extract into somewhere easy to reuse:
fail! errors to propagate taken from this comment on GitHub.
Since it’s easy to get lost in what parts of a context is input or output, I found that it helps to document what each interactor’s inputs and outputs are.
Many scenarios involving interactors can be done using plain Ruby modules. Consider if the addition of a gem like interactor is worth it over writing service objects in a different way.