Interaktor

DISCLAIMER: Interaktor is under active development. Feel free to use it, but until 1.0 is released, any update could break compatibility with an older version.

Interaktor is a fork of Interactor by collectiveidea. While Interactor is still used by collectiveidea internally, communication and progress has been slow in adapting to pull requests and issues. This inactivity combined with my desire to dial back on the Interactor's inherent permissivity led me to fork it and create Interaktor.

Fundamentally, Interaktor is the same as Interactor, but with the following changes:

• Required explicit definition of interaktor "attributes" which replaces the concept of the interaktor context. Attributes are defined using a schema DSL provided by dry-schema, which allows for complex validation, if desired.
• The interaktor "context" is no longer a public-facing concept, all data/attribute accessors/setters are defined as attributes
• Attributes passed to #fail! must be defined in advance
• Interaktors support early-exit functionality through the use of #success!, which functions the same as #fail! in that you must define the required success attributes on the interaktor

Getting started

Add interaktor to your Gemfile and bundle install.

gem "interaktor"

What is an interaktor?

An interaktor is a simple, single-purpose object.

Interaktors are used to encapsulate your application's business logic. Each interaktor represents one thing that your application does.

Attributes

Input attributes

Depending on its definition, an interaktor may require attributes to be passed in when it is invoked. These attributes contain everything the interaktor needs to do its work.

Attributes are defined using a schema DSL provided by the dry-schema gem. It allows the construction of schemas for validating attributes. The schema is typically provided as a block argument to the input class method as seen below.

This example is an extremely simple case, and dry-schema supports highly complex schema validation, like type checking, nested hash data validation, and more. For more information on defining an attribute schema, please see the dry-schema documentation website. This link should take you to the latest version of dry-schema, but be sure to check that the version of dry-schema in your application bundle matches the documentation you are viewing.

class CreateUser
  include Interaktor

  input do
    required(:name)
    optional(:email)
  end

  def call
    User.create!(
      name: name,
      email: email,
    )
  end
end

CreateUser.call(name: "Foo Bar")

input will also accept a Dry::Schema::Params object directly, if for some reason the schema needs to be constructed elsewhere.

A note about type checking: Type checking is cool, but Ruby is a dynamic language, and Ruby developers tend to utilize the idea of duck typing. Forcing the attributes of an interaktor to be of a certain type in order to validate might sound like a good idea, but it can often cause problems in situations where you might like to use duck typing, for example, when using stubs in tests.

Output attributes

Based on the outcome of the interaktor's work, we can require certain attributes. In the example below, we must succeed with a user_id attribute, and if we fail, we must provide an error_messages attribute.

The use of #success! allows you to early-return from an interaktor's work. If no success attribute is provided, and the call method finishes execution normally, then the interaktor is considered to be in a successful state.

class CreateUser
  include Interaktor

  input do
    required(:name).filled(:string)
  end

  success do
    required(:user_id).value(:integer)
  end

  failure do
    required(:error_messages).value(array[:string])
  end

  def call
    user = User.new(name: name)

    if user.save
      success!(user_id: user.id)
    else
      fail!(error_messages: user.errors.full_messages)
    end
  end
end

result = CreateUser.call(name: "Foo Bar")

if result.success?
  puts "The new user ID is: #{result.user_id}".
else
  puts "Creating the user failed: #{result.error_messages.join(", ")}".
end

Dealing with failure

#fail! always throws an exception of type Interaktor::Failure.

Normally, however, these exceptions are not seen. In the recommended usage, the caller invokes the interaktor using the class method .call, then checks the #success? method of the returned object. This works because the call class method swallows exceptions. When unit testing an interaktor, if calling custom business logic methods directly and bypassing call, be aware that fail! will generate such exceptions.

See Interaktors in the controller, below, for the recommended usage of .call and #success?.

Hooks

Before hooks

Sometimes an interaktor needs to prepare something before the interaktor is even run. This can be done with before hooks on the interaktor.

before do
  # Do some stuff
end

A symbol argument can also be given, rather than a block.

before :do_some_stuff

def do_some_stuff
  # Do some stuff
end

After hooks

Interaktors can also perform teardown operations after the interaktor instance is run. They are only run on success.

after do
  user.reload
end

Ensure hooks

Very similar to after hooks, but the hooks are run in an ensure block in the order they are defined.

ensure_hook do
  file.close
end

Around hooks

You can also define around hooks in the same way as before or after hooks, using either a block or a symbol method name. The difference is that an around block or method accepts a single argument. Invoking the call method on that argument will continue invocation of the interaktor. For example, with a block:

around do |interaktor|
  # Do stuff before
  interaktor.call
  # Do stuff after
end

With a method:

around :do_stuff_around

def do_stuff_around(interaktor)
  # Do stuff before
  interaktor.call
  # Do stuff after
end

If #fail! is called, any code defined in the hook after the call to the interaktor will not be run.

Hook sequence

Before hooks are invoked in the order in which they were defined while after hooks are invoked in the opposite order. Around hooks are invoked outside of any defined before and after hooks. For example:

around do |interaktor|
  puts "around before 1"
  interaktor.call
  puts "around after 1"
end

around do |interaktor|
  puts "around before 2"
  interaktor.call
  puts "around after 2"
end

before do
  puts "before 1"
end

before do
  puts "before 2"
end

after do
  puts "after 1"
end

after do
  puts "after 2"
end

will output:

around before 1
around before 2
before 1
before 2
after 2
after 1
around after 2
around after 1

Interaktor concerns

An interaktor can define multiple before/after hooks, allowing common hooks to be extracted into interaktor concerns.

module InteraktorDoStuff
  extend ActiveSupport::Concern

  included do
    around do |interaktor|
      # Do stuff before
      interaktor.call
      # Do stuff after
    end
  end
end

Kinds of interaktors

There are two kinds of interaktors built into the Interaktor library: basic interaktors and organizers.

Interaktors

A basic interaktor is a class that includes Interaktor and defines call.

class AuthenticateUser
  include Interaktor

  input do
    required(:email).filled(:string)
    required(:password).filled(:string)
  end

  success do
    required(:user)
    required(:token).filled(:string)
  end

  failure do
    required(:message).filled(:string)
  end

  def call
    if user = User.authenticate(email, password)
      success!(user: user, token: user.secret_token)
    else
      fail!(message: "authenticate_user.failure")
    end
  end
end

Basic interaktors are the building blocks. They are your application's single-purpose units of work.

Organizers

An organizer is an important variation on the basic interaktor. Its single purpose is to run other interaktors.

class PlaceOrder
  include Interaktor::Organizer

  input do
    required(:order_params).filled(:hash)
  end

  organize CreateOrder, ChargeCard, SendThankYou
end

In the controller, you can run the PlaceOrder organizer just like you would any other interaktor:

class OrdersController < ApplicationController
  def create
    result = PlaceOrder.call(order_params: order_params)

    if result.success?
      redirect_to result.order
    else
      @order = result.order
      render :new
    end
  end

  private

  def order_params
    params.require(:order).permit!
  end
end

The organizer passes any of its own defined attributes into first interaktor that it organizes. That first interaktor is then called and executed using those attributes. For the following interaktors in the organize list, each interaktor receives its attributes from the previous interaktor (both input attributes and success attributes). Any attributes which are not accepted by the next interaktor (listed as required or optional attributes) are dropped in the transition.

Rollback

If any one of the organized interaktors fails, the organizer stops. If the ChargeCard interaktor fails, SendThankYou is never called.

In addition, any interaktors that had already run are given the chance to undo themselves, in reverse order. Simply define the rollback method on your interaktors.

class CreateOrder
  include Interaktor

  input do
    required(:order_params).filled(:hash)
  end

  success do
    required(:order)
  end

  def call
    order = Order.create(order_params)

    if order.persisted?
      success!(order: order)
    else
      fail!
    end
  end

  def rollback
    order.destroy
  end
end

NOTE: The interaktor that fails is not rolled back. Because every interaktor should have a single purpose, there should be no need to clean up after any failed interaktor. This is why the rollback method above can access the order success attribute - rollback is only called on successful interaktors.

Testing interaktors

When written correctly, an interaktor is easy to test because it only does one thing. Take the following interaktor:

class AuthenticateUser
  include Interaktor

  input do
    required(:email).filled(:string)
    required(:password).filled(:string)
  end

  success do
    required(:user)
    required(:token).filled(:string)
  end

  failure do
    required(:message).filled(:string)
  end

  def call
    if user = User.authenticate(email, password)
      success!(user: user, token: user.secret_token)
    else
      fail!(message: "authenticate_user.failure")
    end
  end
end

You can test just this interaktor's single purpose and how it affects the result.

describe AuthenticateUser do
  subject(:result) { AuthenticateUser.call(email: "[email protected]", password: "secret") }

  describe ".call" do
    context "when given valid credentials" do
      let(:user) { double(:user, secret_token: "token") }

      before do
        allow(User).to receive(:authenticate).with("[email protected]", "secret").and_return(user)
      end

      it "succeeds" do
        expect(result).to be_a_success
      end

      it "provides the user" do
        expect(result.user).to eq(user)
      end

      it "provides the user's secret token" do
        expect(result.token).to eq("token")
      end
    end

    context "when given invalid credentials" do
      before do
        allow(User).to receive(:authenticate).with("[email protected]", "secret").and_return(nil)
      end

      it "fails" do
        expect(result).to be_a_failure
      end

      it "provides a failure message" do
        expect(result.message).to be_present
      end
    end
  end
end

Isolation

You may notice that we stub User.authenticate in our test rather than creating users in the database. That's because our purpose in spec/interaktors/authenticate_user_spec.rb is to test just the AuthenticateUser interaktor. The User.authenticate method is put through its own paces in spec/models/user_spec.rb.

It's a good idea to define your own interfaces to your models. Doing so makes it easy to draw a line between which responsibilities belong to the interaktor and which to the model. The User.authenticate method is a good, clear line. Imagine the interaktor otherwise:

class AuthenticateUser
  include Interaktor

  input do
    required(:email).filled(:string)
    required(:password).filled(:string)
  end

  success do
    required(:user)
  end

  failure do
    required(:message).filled(:string)
  end

  def call
    user = User.find_by(email: email)

    # Yuck!
    if user && BCrypt::Password.new(user.password_digest) == password
      success!(user: user)
    else
      fail!(message: "authenticate_user.failure")
    end
  end
end

It would be very difficult to test this interaktor in isolation and even if you did, as soon as you change your ORM or your encryption algorithm (both model concerns), your interaktors (business concerns) break.

Draw clear lines.

Integration

While it's important to test your interaktors in isolation, it's just as important to write good integration or acceptance tests.

One of the pitfalls of testing in isolation is that when you stub a method, you could be hiding the fact that the method is broken, has changed or doesn't even exist.

When you write full-stack tests that tie all of the pieces together, you can be sure that your application's individual pieces are working together as expected. That becomes even more important when you add a new layer to your code like interaktors.

Controllers

One of the advantages of using interaktors is how much they simplify controllers and their tests. Because you're testing your interaktors thoroughly in isolation as well as in integration tests (right?), you can remove your business logic from your controller tests.

class SessionsController < ApplicationController
  def create
    result = AuthenticateUser.call(session_params)

    if result.success?
      session[:user_token] = result.token
      redirect_to result.user
    else
      flash.now[:message] = t(result.message)
      render :new
    end
  end

  private

  def session_params
    params.require(:session).permit(:email, :password)
  end
end

describe SessionsController do
  describe "#create" do
    before do
      expect(AuthenticateUser).to receive(:call).once.with(email: "[email protected]", password: "secret").and_return(result)
    end

    context "when successful" do
      let(:user) { double(:user, id: 1) }
      let(:result) { double(:result, success?: true, user: user, token: "token") }

      it "saves the user's secret token in the session" do
        expect {
          post :create, session: { email: "[email protected]", password: "secret" }
        }.to change {
          session[:user_token]
        }.from(nil).to("token")
      end

      it "redirects to the homepage" do
        response = post :create, session: { email: "[email protected]", password: "secret" }

        expect(response).to redirect_to(user_path(user))
      end
    end

    context "when unsuccessful" do
      let(:result) { double(:result, success?: false, message: "message") }

      it "sets a flash message" do
        expect {
          post :create, session: { email: "[email protected]", password: "secret" }
        }.to change {
          flash[:message]
        }.from(nil).to(I18n.translate("message"))
      end

      it "renders the login form" do
        response = post :create, session: { email: "[email protected]", password: "secret" }

        expect(response).to render_template(:new)
      end
    end
  end
end

This controller test will have to change very little during the life of the application because all of the magic happens in the interaktor.

Rails

Interactor provided interactor-rails, which ensures app/interactors is included in your autoload paths, and provides generators for new interactors. I have no intention of maintaining generators but if someone feels strongly enough to submit a pull request to include the functionality in this gem (not a separate Rails one) then I will be happy to take a look. Making sure app/interaktors is included in your autoload paths is something I would like to do soon.