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Actor

Tests

This Ruby gem lets you move your application logic into into small composable service objects. It is a lightweight framework that helps you keep your models and controllers thin.

Photo of theater seats

Contents

Installation

Add these lines to your application’s Gemfile:

# Composable service objects
gem "service_actor"

When using Rails, you can include the service_actor-rails gem:

# Composable service objects
gem "service_actor-rails"

Usage

Actors are single-purpose actions in your application that represent your business logic. They start with a verb, inherit from Actor and implement a call method.

# app/actors/send_notification.rb
class SendNotification < Actor
  def call
    # …
  end
end

Trigger them in your application with .call:

SendNotification.call # => <ServiceActor::Result…>

When called, actors return a Result. Reading and writing to this result allows actors to accept and return multiple arguments. Let’s find out how to do that and then we’ll see how to chain multiple actors togethor.

Inputs

To accept arguments, use input to create a method named after this input:

class GreetUser < Actor
  input :user

  def call
    puts "Hello #{user.name}!"
  end
end

You can now call your actor by providing the correct arguments:

GreetUser.call(user: User.first)

Outputs

An actor can return multiple arguments. Declare them using output, which adds a setter method to let you modify the result from your actor:

class BuildGreeting < Actor
  output :greeting

  def call
    self.greeting = "Have a wonderful day!"
  end
end

The result you get from calling an actor will include the outputs you set:

result = BuildGreeting.call
result.greeting # => "Have a wonderful day!"

For each output a method is generated ending with a ?, which is useful when the output is used for conditional control flow, like if-else statements.

if result.greeting?
  puts "Greetings is a non empty value"
else
  puts "Greetings is empty"
end

The generated method will return the truthy or falsey values of variables.

Defaults

Inputs can be marked as optional by providing a default:

class BuildGreeting < Actor
  input :name
  input :adjective, default: "wonderful"
  input :length_of_time, default: -> { ["day", "week", "month"].sample }

  output :greeting

  def call
    self.greeting = "Have a #{adjective} #{length_of_time} #{name}!"
  end
end

This lets you call the actor without specifying those keys:

result = BuildGreeting.call(name: "Jim")
result.greeting # => "Have a wonderful week Jim!"

If an input does not have a default, it will raise a error:

result = BuildGreeting.call
=> ServiceActor::ArgumentError: Input name on BuildGreeting is missing.

Conditions

You can ensure an input is included in a collection by using in:

class Pay < Actor
  input :currency, in: %w[EUR USD]

  # …
end

This raises an argument error if the input does not match one of the given values.

You can also add custom conditions with the name of your choice by using must:

class UpdateAdminUser < Actor
  input :user,
        must: {
          be_an_admin: ->(user) { user.admin? }
        }

  # …
end

This raises an argument error if the given lambda returns a falsey value.

Allow nil

By default inputs accept nil values. To raise an error instead:

class UpdateUser < Actor
  input :user, allow_nil: false

  # …
end

Types

Sometimes it can help to have a quick way of making sure we didn’t mess up our inputs.

For that you can use the type option and giving a class or an array of possible classes. If the input or output doesn’t match these types, an error is raised.

class UpdateUser < Actor
  input :user, type: User
  input :age, type: [Integer, Float]

  # …
end

You may also use strings instead of constants, such as type: "User".

When using a type condition, allow_nil defaults to false.

Fail

To stop the execution and mark an actor as having failed, use fail!:

class UpdateUser
  input :user
  input :attributes

  def call
    user.attributes = attributes

    fail!(error: "Invalid user") unless user.valid?

    # …
  end
end

This will raise an error in your app with the given data added to the result.

To test for the success of your actor instead of raising an exception, use .result instead of .call. You can then call success? or failure? on the result.

For example in a Rails controller:

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def create
    result = UpdateUser.result(user: user, attributes: user_attributes)
    if result.success?
      redirect_to result.user
    else
      render :new, notice: result.error
    end
  end
end

The keys you add to fail! will be added to the result, for example you could do: fail!(error_type: "validation", error_code: "uv52", …).

Play actors in a sequence

To help you create actors that are small, single-responsibility actions, an actor can use play to call other actors:

class PlaceOrder < Actor
  play CreateOrder,
       Pay,
       SendOrderConfirmation,
       NotifyAdmins
end

This creates a call method that will call every actor along the way. Inputs and outputs will go from one actor to the next, all sharing the same result set until it is finally returned.

Rollback

When using play, when an actor calls fail!, the following actors will not be called.

Instead, all the actors that succeeded will have their rollback method called in reverse order. This allows actors a chance to cleanup, for example:

class CreateOrder < Actor
  output :order

  def call
    self.order = Order.create!(…)
  end

  def rollback
    order.destroy
  end
end

Rollback is only called on the previous actors in play and is not called on the failing actor itself. Actors should be kept to a single purpose and not have anything to clean up if they call fail!.

Lambdas

You can use inline actions using lambdas. Inside these lambdas you have access to the shared result:

class Pay < Actor
  play ->(result) { result.payment_provider = "stripe" },
       CreatePayment,
       ->(result) { result.user_to_notify = result.payment.user },
       SendNotification
end

Like in this example, lambdas can be useful for small work or preparing the result for the next actors. If you want to do more work before, after or around the whole play, you can also override the call method. For example:

class Pay < Actor
  # …

  def call
    Time.with_timezone("Paris") do
      super
    end
  end
end

Play conditions

Actors in a play can be called conditionally:

class PlaceOrder < Actor
  play CreateOrder,
       Pay
  play NotifyAdmins, if: ->(result) { result.order.amount > 42 }
end

You can use this to trigger an early success.

Fail on argument error

By default, errors on inputs will raise an error, even when using .result instead of .call. If instead you want to mark the actor as failed, you can catch the exception to treat it as an actor failure:

class PlaceOrder < Actor
  fail_on ServiceActor::ArgumentError

  input :currency, in: ["EUR", "USD"]

  # …
end

Testing

In your application, add automated testing to your actors as you would do to any other part of your applications.

You will find that cutting your business logic into single purpose actors will make it easier for you to test your application.

Build your own actor

If you application already uses a class called “Actor”, you can build your own by changing the gem’s require statement:

gem "service_actor", require: "service_actor/base"

And building your own class to inherit from:

class ApplicationActor
  include ServiceActor::Base
end

Influences

This gem is heavily influenced by Interactor ♥. Some key differences make Actor unique:

  • Does not hide errors when an actor fails inside another actor.
  • Requires you to document all arguments with input and output.
  • Defaults to raising errors on failures: actor uses call and result instead of call! and call. This way, the default is to raise an error and failures are not hidden away because you forgot to use !.
  • Allows defaults, type checking, requirements and conditions on inputs.
  • Delegates methods on the context: foo vs context.foo, self.foo = vs context.foo = , fail! vs context.fail!.
  • Shorter setup syntax: inherit from < Actor vs having to include Interactor and include Interactor::Organizer.
  • Organizers allow lambdas, being called multiple times, and having conditions.
  • Allows early success with conditions inside organizers.
  • No before, after and around hooks, prefer using play with lambdas or overriding call.

Actor supports mixing actors & interactors when using play for a smooth migration.

Thanks

Thank you to @nicoolas25, @AnneSottise & @williampollet for the early thoughts and feedback on this gem.

Photo by Lloyd Dirks.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run bin/rake to run the tests and linting. You can also run bin/console for an interactive prompt.

To release a new version, update the version number in version.rb, and in the CHANGELOG.md. Update the README.md if there are missing segments, make sure tests and linting are pristine by calling bundle && bin/rake, then create a commit for this version.

You can then run rake release, which will assign a git tag, push using git, and push the gem to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub.

This project is intended to be a safe, welcoming space for collaboration, and everyone interacting in the project’s codebase and issue tracker is expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.