CivilService

CivilService is a tiny framework for service objects in Rails apps. With CivilService, you can use ActiveModel validations to do pre-flight checks before the service runs, and create your own result object classes to capture the results of complex operations.

CivilService was extracted from Intercode, a web app for convention organizers and participants. It is now maintained by ActBlue.

Add this line to your application's Gemfile:

gem 'civil_service'

And then execute:

$ bundle

Or install it yourself as:

$ gem install civil_service

CivilService::Service is really a pretty tiny class. It does, however, have some opinions that create a potentially-useful abstraction for app developers:

• When called, services always return a result object that responds to (at least) #success?, #failure?, #errors, and #exception. This lets your code paths that call services be consistent and simple. (If you want to return more information as a result of running the service, it's easy to define a custom result class for your service.)
  • What's the difference between #errors and #exception? #errors is an instance of ActiveModel::Errors, whereas #exception is an instance of an exception class (it's only present if an exception was raised inside the service call). If an exception is raised, the service result will respond true to #failure?, false to #success?, and the exception's message will be added to #errors, so most of the time you can ignore #exception - but it's there in case you need to dig into the details.
• Services include ActiveModel::Validations so they can easily do pre-flight checks. That means you can call my_service.valid? and my_service.errors just like you can for a model, and it also means that the service will fail if it's not valid.
• In addition to #call, which always returns a result object, services have a #call! method, which will raise a CivilService::ServiceFailure exception if the service fails, or pass through an exception if one is raised inside the service call. This might be easier in some workflows; for example, it will cause a rollback if used inside an ActiveRecord transaction block.
• Finally, there's a third variant: #call_and_raise, which will re-raise any exceptions that occurred during the service execution, but will return a regular result object on failure.

Here's a simple service that changes a user's password in a hypothetical Rails app, and sends a notification email about it:

class PasswordChangeService < CivilService::Service
  validate :ensure_valid_password

  attr_reader :user, :new_password

  def initialize(user:, new_password:)
    @user = user
    @new_password = new_password
  end

  private

  def inner_call
    user.update!(password: new_password)
    UserMailer.password_changed(user).deliver_later
    success
  end

  def ensure_valid_password
    return if new_password.length >= 8
    errors.add(:base, "Passwords must be at least 8 characters long")
  end
end

You might call this from a controller action like this:

class UsersController < ApplicationController
  def change_password
    service = PasswordChangeService.new(user: current_user, new_password: params[:password])
    result = service.call

    if result.success?
      redirect_to root_url, notice: "Your password has been changed."
    else
      flash[:alert] = result.errors.full_messages.join(', ')
    end
  end
end

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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/actblue/civil_service.