Scoped Concerns

Scoped-Concerns is a tiny utility library to help you encapsulate responsibilities in your Ruby applications by providing a common interface and a common response object for the so called service classes or how we like to call them: concerns.

We've been playing around with this concept in a few applications and it was evolving until this point that we feel it reusable enough to become a separated library.

Install

It's a Ruby gem in rubygems.org, so is as simple as:

gem install scoped-concerns

Usage

Include Scoped::Concern in your service (concern) class, and implement your constructor and the run methods with the logic for your domain. For example

module MyApp
  module Concerns
    class ActivateUser
      include Scoped::Concern

      def initialize(params = {})
        @user_id = params[:user_id]
      end

      def run
        user = User.find(@user_id)
        return error(user: [:not_valid]) unless user

        begin
          user.activate!
          success(user: "Activated")
        rescue => e
          logger.log(e.message)
          error(update: [:not_valid])
        end
      end
    end
  end
end

Then you can use this concern in your endpoints logic, like:

on "activate/:id" do |id|
  response = MyApp::Concerns::ActivateUser.run(user_id: id)

  if response.success?
    json(message: "User has been activated")
  else
    json_error(message: [response.errors[:update], response.errors[:user]].join("\n"))
  end
end

Scoped-Concerns provides the run, error and success helper methods through Concern module and the Scoped::Response class as a standard response format.

Scoped-Concerns proposes the following conventions:

• Parameters to a concern should always be a Hash, even if you need only one parameter (see example above)
• A Concern should always return a Scoped::Response object. (success and error helper methods return this)

Response

The Scoped::Response class has the result and errors attributes, both of them must be hashes. The keys of these Hashes will depend on your application domain, but, at least, you know that you'll deal with Hashes.

The Scoped::Response class also has a success? instance utility method that is a wrapper to @errors.empty? for readability's sake.