Interactor
Getting Started
Add Interactor to your Gemfile and bundle install
.
gem "interactor", "~> 3.0"
What is an Interactor?
An interactor is a simple, single-purpose object.
Interactors are used to encapsulate your application's business logic. Each interactor represents one thing that your application does.
Context
An interactor is given a context. The context contains everything the interactor needs to do its work.
When an interactor does its single purpose, it affects its given context.
Adding to the Context
As an interactor runs it can add information to the context.
context.user = user
Failing the Context
When something goes wrong in your interactor, you can flag the context as failed.
context.fail!
When given a hash argument, the fail!
method can also update the context. The
following are equivalent:
context.error = "Boom!"
context.fail!
context.fail!(error: "Boom!")
You can ask a context if it's a failure:
context.failure? # => false
context.fail!
context.failure? # => true
or if it's a success.
context.success? # => true
context.fail!
context.success? # => false
Dealing with Failure
context.fail!
always throws an exception of type Interactor::Failure
.
Normally, however, these exceptions are not seen. In the recommended usage, the controller invokes the interactor using the class method call
, then checks the success?
method of the context.
This works because the call
class method swallows exceptions. When unit testing an interactor, if calling custom business logic methods directly and bypassing call
, be aware that fail!
will generate such exceptions.
See Interactors in the Controller, below, for the recommended usage of call
and success?
.
Hooks
Before Hooks
Sometimes an interactor needs to prepare its context before the interactor is even run. This can be done with before hooks on the interactor.
before do
context.emails_sent = 0
end
A symbol argument can also be given, rather than a block.
before :zero_emails_sent
def zero_emails_sent
context.emails_sent = 0
end
After Hooks
Interactors can also perform teardown operations after the interactor instance is run.
after do
context.user.reload
end
NB: After hooks are only run on success. If the fail!
method is called, the interactor's after hooks are not run.
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 interactor. For example, with a block:
around do |interactor|
context.start_time = Time.now
interactor.call
context.finish_time = Time.now
end
With a method:
around :time_execution
def time_execution(interactor)
context.start_time = Time.now
interactor.call
context.finish_time = Time.now
end
NB: If the fail!
method is called, all of the interactor's around hooks cease execution, and no code after interactor.call
will 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 |interactor|
puts "around before 1"
interactor.call
puts "around after 1"
end
around do |interactor|
puts "around before 2"
interactor.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
Interactor Concerns
An interactor can define multiple before/after hooks, allowing common hooks to be extracted into interactor concerns.
module InteractorTimer
extend ActiveSupport::Concern
included do
around do |interactor|
context.start_time = Time.now
interactor.call
context.finish_time = Time.now
end
end
end
An Example Interactor
Your application could use an interactor to authenticate a user.
class AuthenticateUser
include Interactor
def call
if user = User.authenticate(context.email, context.password)
context.user = user
context.token = user.secret_token
else
context.fail!(message: "authenticate_user.failure")
end
end
end
To define an interactor, simply create a class that includes the Interactor
module and give it a call
instance method. The interactor can access its
context
from within call
.
Interactors in the Controller
Most of the time, your application will use its interactors from its controllers. The following controller:
class SessionsController < ApplicationController
def create
if user = User.authenticate(session_params[:email], session_params[:password])
session[:user_token] = user.secret_token
redirect_to user
else
flash.now[:message] = "Please try again."
render :new, status: :unprocessable_entity
end
end
private
def session_params
params.require(:session).permit(:email, :password)
end
end
can be refactored to:
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, status: :unprocessable_entity
end
end
private
def session_params
params.require(:session).permit(:email, :password)
end
end
The call
class method is the proper way to invoke an interactor. The hash
argument is converted to the interactor instance's context. The call
instance
method is invoked along with any hooks that the interactor might define.
Finally, the context (along with any changes made to it) is returned.
When to Use an Interactor
Given the user authentication example, your controller may look like:
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
For such a simple use case, using an interactor can actually require more code. So why use an interactor?
Clarity
We often use interactors right off the bat for all
of our destructive actions (POST
, PUT
and DELETE
requests) and since we
put our interactors in app/interactors
, a glance at that directory gives any
developer a quick understanding of everything the application does.
▾ app/
▸ controllers/
▸ helpers/
▾ interactors/
authenticate_user.rb
cancel_account.rb
publish_post.rb
register_user.rb
remove_post.rb
▸ mailers/
▸ models/
▸ views/
TIP: Name your interactors after your business logic, not your
implementation. CancelAccount
will serve you better than DestroyUser
as the
account cancellation interaction takes on more responsibility in the future.
The Future™
SPOILER ALERT: Your use case won't stay so simple.
In our experience, a simple task like authenticating a user will eventually take on multiple responsibilities:
- Welcoming back a user who hadn't logged in for a while
- Prompting a user to update his or her password
- Locking out a user in the case of too many failed attempts
- Sending the lock-out email notification
The list goes on, and as that list grows, so does your controller. This is how fat controllers are born.
If instead you use an interactor right away, as responsibilities are added, your controller (and its tests) change very little or not at all. Choosing the right kind of interactor can also prevent simply shifting those added responsibilities to the interactor.
Kinds of Interactors
There are two kinds of interactors built into the Interactor library: basic interactors and organizers.
Interactors
A basic interactor is a class that includes Interactor
and defines call
.
class AuthenticateUser
include Interactor
def call
if user = User.authenticate(context.email, context.password)
context.user = user
context.token = user.secret_token
else
context.fail!(message: "authenticate_user.failure")
end
end
end
Basic interactors are the building blocks. They are your application's single-purpose units of work.
Organizers
An organizer is an important variation on the basic interactor. Its single purpose is to run other interactors.
class PlaceOrder
include Interactor::Organizer
organize CreateOrder, ChargeCard, SendThankYou
end
In the controller, you can run the PlaceOrder
organizer just like you would
any other interactor:
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 its context to the interactors that it organizes, one at a time and in order. Each interactor may change that context before it's passed along to the next interactor.
Rollback
If any one of the organized interactors fails its context, the organizer stops.
If the ChargeCard
interactor fails, SendThankYou
is never called.
In addition, any interactors that had already run are given the chance to undo
themselves, in reverse order. Simply define the rollback
method on your
interactors:
class CreateOrder
include Interactor
def call
order = Order.create(order_params)
if order.persisted?
context.order = order
else
context.fail!
end
end
def rollback
context.order.destroy
end
end
NOTE: The interactor that fails is not rolled back. Because every interactor should have a single purpose, there should be no need to clean up after any failed interactor.
Testing Interactors
When written correctly, an interactor is easy to test because it only does one thing. Take the following interactor:
class AuthenticateUser
include Interactor
def call
if user = User.authenticate(context.email, context.password)
context.user = user
context.token = user.secret_token
else
context.fail!(message: "authenticate_user.failure")
end
end
end
You can test just this interactor's single purpose and how it affects the context.
describe AuthenticateUser do
subject(:context) { AuthenticateUser.call(email: "john@example.com", 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("john@example.com", "secret").and_return(user)
end
it "succeeds" do
expect(context).to be_a_success
end
it "provides the user" do
expect(context.user).to eq(user)
end
it "provides the user's secret token" do
expect(context.token).to eq("token")
end
end
context "when given invalid credentials" do
before do
allow(User).to receive(:authenticate).with("john@example.com", "secret").and_return(nil)
end
it "fails" do
expect(context).to be_a_failure
end
it "provides a failure message" do
expect(context.message).to be_present
end
end
end
end
We use RSpec but the same approach applies to any testing framework.
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/interactors/authenticate_user_spec.rb
is to test just the
AuthenticateUser
interactor. 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 interactor and
which to the model. The User.authenticate
method is a good, clear line.
Imagine the interactor otherwise:
class AuthenticateUser
include Interactor
def call
user = User.where(email: context.email).first
# Yuck!
if user && BCrypt::Password.new(user.password_digest) == context.password
context.user = user
else
context.fail!(message: "authenticate_user.failure")
end
end
end
It would be very difficult to test this interactor in isolation and even if you did, as soon as you change your ORM or your encryption algorithm (both model concerns), your interactors (business concerns) break.
Draw clear lines.
Integration
While it's important to test your interactors 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 interactors.
TIP: If you track your test coverage, try for 100% coverage before integrations tests. Then keep writing integration tests until you sleep well at night.
Controllers
One of the advantages of using interactors is how much they simplify controllers and their tests. Because you're testing your interactors 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: "john@doe.com", password: "secret").and_return(context)
end
context "when successful" do
let(:user) { double(:user, id: 1) }
let(:context) { double(:context, success?: true, user: user, token: "token") }
it "saves the user's secret token in the session" do
expect {
post :create, session: { email: "john@doe.com", password: "secret" }
}.to change {
session[:user_token]
}.from(nil).to("token")
end
it "redirects to the homepage" do
response = post :create, session: { email: "john@doe.com", password: "secret" }
expect(response).to redirect_to(user_path(user))
end
end
context "when unsuccessful" do
let(:context) { double(:context, success?: false, message: "message") }
it "sets a flash message" do
expect {
post :create, session: { email: "john@doe.com", password: "secret" }
}.to change {
flash[:message]
}.from(nil).to(I18n.translate("message"))
end
it "renders the login form" do
response = post :create, session: { email: "john@doe.com", 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 interactor.
Rails
We love Rails, and we use Interactor with Rails. We
put our interactors in app/interactors
and we name them as verbs:
AddProductToCart
AuthenticateUser
PlaceOrder
RegisterUser
RemoveProductFromCart
See: Interactor Rails
Contributions
Interactor is open source and contributions from the community are encouraged! No contribution is too small.
See Interactor's contribution guidelines for more information.
Thank You
A very special thank you to Attila Domokos for his fantastic work on LightService. Interactor is inspired heavily by the concepts put to code by Attila.
Interactor was born from a desire for a slightly simplified interface. We understand that this is a matter of personal preference, so please take a look at LightService as well!