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 (email
, name
) and returns output (user
):
result = RegisterUser.call( email: 'hi@example.com', name: 'John')result.success? # => trueresult.user # => User
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.
module RegisterUser include Interactor
def call create_user create_profile track_analytics end
def create_user context.user = User.create( email: context.email, is_admin: context.is_admin || false ) end
def create_profile context.profile = Profile.create( user_id: context.user.id, name: context.name ) end
def track_analytics Analytics.track('NEW_USER', uid: context.user.id) endend
RegisterUser.call(email: 'hi@example.com', name: 'John')result.success? # => trueresult.email # => string (input)result.is_admin # => string (input)result.profile # => Profile (output)result.user # => <User> (output)
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.
module RegisterUser include Interactor::Organizer organize( CreateUserRecord, CreateProfile, TrackAnalytics )end
module CreateUserRecord include Interactor def call user = User.new(context.email, context.is_admin) # Input context.user = user # Output endend
module CreateProfile include Interactor def call profile = Profile.new(context.user, context.email) # Input context.profile = profile # Output endend
module TrackAnalytics include Interactor def call user = context.user # Input Analytics.track!(user.id) endend
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.)
Interactor | is_admin | user | profile | |
---|---|---|---|---|
RegisterUser | in | in | out | out |
… CreateUserRecord | in | in | out | |
… CreateProfile | in | out | ||
… TrackAnalytics | in |
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.
module ValidateEmail include Interactor def call email = context.email
unless EMAIL_REGEXP.match(email) context.fail! error: :invalid_format end
if User.where(email: email).count != 0 context.fail! error: :email_is_already_taken end endend
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.
module SendPageToFriend include Interactor::Organizer organize( ValidateEmail, # <-- ! not working as intended! DoSendPageToFriend )end
SendPageToFriend( params: { email: 'hello@example.com', message: 'Have a look!' })
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.
module NestedInteractor def call ValidateEmail.call!(email: context.params.email)
# Question: will an error in the line above # prevent this next line from working? do_work_after_validation endend
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 context.fail!
.
module NestedInteractor def call ValidateEmail.call!(email: context.params.email)
do_work_after_validation
rescue Interactor::Failure => e context.fail!(error: e.context.error) endend
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.
fail!
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:
module MyInteractor include Interactor
def handle_errors(&block) yield rescue Interactor::Failure => e context.fail!(error: e.context.error) endend
# Now errors can be propagated instead of being# silently swallowed:
handle_errors do MyOtherInteractor.call!end
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.
# == Inputs# [user_id] (string) The user ID# [use_defaults] (boolean, optional)## == Outputs# [categories] (Category[])module CreateUseCategories include Interactor
def call; ... endend
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.
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