Ruby interactors: a review
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? # => true
result.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)
end
end
RegisterUser.call(email: 'hi@example.com', name: 'John')
result.success? # => true
result.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, reuseble 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
end
end
module CreateProfile
include Interactor
def call
profile = Profile.new(context.user, context.email) # Input
context.profile = profile # Output
end
end
module TrackAnalytics
include Interactor
def call
user = context.user # Input
Analytics.track!(user.id)
end
end
In this example, the 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 | out | ||
… CreateProfile | in | out | ||
… TrackAnalytics | out |
Interactors are often touted for being useful for managing reuseable 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
end
end
context.email
input, and throws an error if it’s not valid.While this logic is nicely self-contained, it’s not easily reuseable 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
end
end
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)
end
end
rescue
block will be needed when using call!
inside interactors. See the discussion on GitHub.The last release of the interactor and interactor-rails gems are in 2019. There has been plans for a v4 release but those have been put on hold as of Dec 2021. There are still some open issues, such as with the use of nested interactors mentioned above.
Ruby 3.0 comes with static type checking. However, with context
being shared as both input and output, type definitions can become ambiguous. Interactors don’t support static typing yet, but consider this hypothetical example below that shows how difficult it would be to add types.
# RBS type definitions
module RegisterUser
def self.call: (context: RegisterUserContext) -> void
end
class RegisterUserContext extends Interactor::Context
email: string
is_admin: boolean | nil
user: User | nil
profile: Profile | nil
end
RegisterUserContext
will be shared across all sub-interactors. Some devs might confuse why user
is optional: is it because its an output, or because its an optional input?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:
module MyInteractor
include Interactor
def handle_errors(&block)
yield
rescue Interactor::Failure => e
context.fail!(error: e.context.error)
end
end
# 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; ... end
end
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.