Actionizer

This gem is an implementation of the Interactor pattern. This pattern has also been called Ports and Adapters or Hexagonal Architecture or DCI (Data-Context-Interaction) but the ideas are pretty much the same. Its goal is to provide a simple pattern for writing truly single-purpose classes. These classes are then easy to reason about, easy to test, and easy to change. They aren't coupled to all sorts of other parts of your system; they are self-contained and perform one and only one action.

This is not remotely a new or unique idea as there have been many awesome articles and previous projects written to implement clean, modular classes. Uncle Bob even wrote a great post highlighting similarities between the big architectural ideas of the last decade or so. While you should totally go read that article, I'll summarize it here for you. Your app is not your framework. It's super effective to decouple your business logic from your framework, database, UI, and third-party APIs.

I like to think of your business logic as being the "gooey center" of your app. That's where the most critical code lives. You want to keep it isolated from the details of databases, file systems, and networks. This inner layer should be so simple as to be boring because it's crucial to get it correct, so you want to make the code clean and simple, even stupid simple. Actionizer will help you write boring, stupid simple code.

Add this line to your application's Gemfile:

gem 'actionizer'

And then run:

$ bundle install

Include Actionizer in your class and define an instance method. That instance method will be automatically invoked when you call the class method of the same name. Any Action defined with Actionizer will automatically return a hash-like result you can check for success? or failure?.

Inputs are available on the input instance variable. Use output to set any variables you want returned in the result.

class CreateUser
  include Actionizer

  def call
    # Some validation here...
    output.user = User.create(name: input.name)
  end
end

Actions are successful by default:

result = SuccessfulAction.call(id: 1234)

result.success?
#=> true
result.failure?
#=> false

You can simplify your controllers drastically having them simply check for success?

class UserController < ApplicationController

  def create
    result = CreateUser.call(name: params.fetch(:name), email: params.fetch(:email))

    if result.success?
      render :dashboard, user: result.user
    else
      redirect_to :new, error: "Couldn't create user because #{result.error_reason}"
    end
  end

end

You can immediately stop execution with the fail! method.

class DeleteAccount
  include Actionizer

  def run
    # Possibly failing code here
    fail!(error: "Nope, didn't work") if failure_condition

    # This code never runs
    output.foo = 'bar'
  end
end

When you fail an action with fail!, the result it returns will return true for failure? and false for success?.

result = FailingAction.call(id: 1234)

result.success?
#=> false
result.failure?
#=> true

The most common way to use Actionizer is to compose small pieces of functionality (which can themselves be Actions) into larger pieces of functionality to give that sequence of Actions a name and simple interface. Say you want to create a user and send them a welcome email as part of the onboarding process. Then you might do something like this:

class OnboardUser
  include Actionizer

  def call
    result = CreateUser.call(name: input.name, email: input.email)
    fail!(error: result.error) if result.failure?

    result = SendWelcomeEmail.deliver_now(name: input.name, email: input.email)
    fail!(error: result.error) if result.failure?
  end
end

This code is self-documenting because there's no wiki or comments to read about what's going on here. The code is telling you exactly what's going on.

To more explicitly document the inputs to your Actions, you can use inputs_for.

class CreateUser
  include Actionizer

  inputs_for(:call) do
    required :name
    required :email
    optional :phone_number
  end
  def call
    result = CreateUser.call(user_params)
  end

  private

  def user_params
    { name: input.name, email: input.email, phone_number: input.phone_number }.compact
  end
end

You can now also optionally specify types and nullability for your inputs. For the type: option, any ruby class can be used.

inputs_for(:call) do
  required :name, type: String, null: false
  required :email, null: false
  optional :phone_number, type: Integer
end

The action will fail immediately if any of the conditions are met:

• Any required param is not passed
• A param is passed that is not declared
• nil is passed for a param marked null: false (default is null: true)
• The class of the argument is not equal to or a subclass of the specified type

Using an inputs_for block is completely opt-in so if you don't provide it, no checking is performed.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests and rubocop -D to check for style errors. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/mikenichols/actionizer. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

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