ActiveOperation is a micro-framework for modelling business processes. It is the perfect companion for any Rails application. The main idea behind an operation is to move code that traditionally either lives in a controller or a model into a dedicated object. Multiple operations can be combined into a pipeline. This helps with structuring large business processes and aids reusability.

Add this line to your application's Gemfile:

gem 'active_operation'

And then execute:

$ bundle

Or install it manually as:

$ gem install active_operation

Run the the install generator to initialize a base operation:

rails g active_operation:install

Then generate the desired operation:

rails g active_operation:operation signup/create_user

We will first look at defining and using a single operation and then explore how to combine multiple operations into a pipeline.

To define an operation, create a new class and inherit from ActiveOperation::Base. The input arguments of an operation are defined using the input statement. These statements describe the arguments the initializer takes. All arguments are accessible through reader and writer methods. ActiveOperation uses SmartProperties to provide this feature. More information on the available configuration options can be found in the project README.

Every operation must implement the #execute method, which describes its core functionality. Additionally, operations support the following callbacks: before, around, after, succeeded, halted, error. The callback mechanism utilizes ActiveSupport::Callbacks. Thus, everything known from Rails is applicable for operation callbacks, too.

# app/operations/user/signup.rb
class User::Signup < ActiveOperation::Base
  input :email, accepts: String, type: :keyword, required: true
  input :password, accepts: String, type: :keyword, required: true

  before do
    user = User.find_by(email: email)
    halt user unless user.nil?
  end

  def execute
    User.create!(email: email, password: password)
  end

  succeeded do
    Email::SendWelcomeMail.perform(output)
  end
end

To execute an operation, instantiate it and invoke the #call method. This method will return the operation's output, which is also available through the #output method. For convenience, operations also expose a .call class method, which instantiates the operation, runs it and returns its output.

Operations go through different states during their lifecycle. After executing an operation, the state can be used for branching purposes. In the example below, the operation's state is used to decide wether to redirect to the user_path or to re-render the new page.

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def create
    signup = User::Signup.new(**signup_params)
    @user = signup.call

    if signup.succeeded?
      redirect_to user_path(@user)
    else
      flash[:error] = "Could not create user"
      render :new
    end
  end

  private

  def signup_params
    params.permit(:email, :password)
  end
end

Continuing with the example above, given the two operations, User::Signup and Email::SendWelcomeEmail, a pipeline can be defined as follows:

class OnboardUser < ActiveSupport::Pipeline
  use User::Signup
  use Email::SendWelcomeEmail
end

The pipeline derives its inputs from the first operation – in this case User::Signup. Similarly, the pipeline's output is simply the output of the last operation. All operations beyond the first operation are expected to take its predecessors output as input. In the example above, User::Signup produces a User record that Email::SendWelcomeEmail takes as input.

Pipeline themselves are operations and can therefore be invoked like any other operations.

OnboardUser.call(email: "[email protected]", password: "123456")

Furthermore, since pipelines are operations themselves, they can also be used within other pipelines.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. 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/t6d/active_operation.

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