The best service object (for us)

Service object

---

Rules

Always call service object, by call method

class Service
  def call
    puts 'hello'
  end
end

Service.new.call

---

Keep call simple and readable, describe its story by methods name

class Service
  def call
    set_as_completed or cancel
  end
end

---

Consider wrapping call methods in transactions

Sometimes when multiple steps are involved to fulfill the responsibility of a service object, it might be a good idea to wrap the steps in a transaction, so that if any of the steps fails, we can always rollback the changes made in previous steps. (2)

USE TRANSACTION ONLY FOR DB OPERATIONS

---

class Service
  def call
    ActiveRecord::Base.transaction do
      assign_line_items
      calcuate_totals
      set_as_completed or cancel
    end
  end
end

---

Return result object as struct

Result = Struct.new(:success, :value) do
  def success?
    success
  end

  def failure?
    !success
  end
end

Result.new(true, "Message sent!")

---

Always call service with params object, by call method and pass dependencies to initialize

class Service
  def initialize(facebook_adapter: FacebookAdapter.new)
    @facebook_adapter = facebook_adapter
  end
  
  def call(params)
    if @facebook_adapter.send_message(params[:user_id, params[:message])
        Result.new(true, "Message was sent")
    else
        Result.new(false, "Some error occured")
    end
  end
end

Service.new.call(123, "Please try Spree Commerce if you need good ecommerce framework")

---

Use private. Usually only initialize and call should be public.

---

Include ServiceObject module.

---

ChainIt

https://github.com/tier-tools/chainit

class UserUpdater
  def call
    ChainIt
      .chain { FindUser.call(1) }
      .chain { UpdateUser.call(email: 'user@example.com') }
      .chain { p :success}
      .result
  end
end

---

ServiceObject module

---

Concern

module ServiceObject
  extend ActiveSupport::Concern

  module ClassMethods
    def call(*args)
      new.call(*args)
    end
  end

  def call
    raise NotImplementedError
  end
end

---

Call shortcut

Service.call(args) instead of Service.new(args).call.

---

Raise exception on call if not defined

Call method is important. Really.

---

Shared examples

shared_examples_for "service object" do
  it { expect(subject.call).to_not raise_error }
end

---

Links

1. The Power of Interfaces in Ruby - Shiroyasha
2. Essential RubyOnRails patterns — part 1: Service Objects
3. A Case For Use Cases - We build Envato
4. Struct inheritance is overused - The Pug Automatic
5. The 3 Tenets of Service Objects in Ruby on Rails – Hacker Noon
6. Chain service objects like a boss – Benjamin roth – Medium