Use one service object per endpoint

Service objects can be used to share code, leading to nested service objects:

Problems 🔗

This makes service objects difficult to reason about.

Result objects also add extra complexity.

Solution 🔗

Use exactly one service object per endpoint.

Don’t nest service objects.

Use domain objects.

What is a domain object? 🔗

  1. Has data and behaviour
  2. Uses business language
  3. Can be a plain old Ruby object or an Active Record object (POROs preferred)

Where are domain objects stored? 🔗

Examples 🔗

Bad 🔗 

class SearchesController < ApplicationController
  def update
    search = Search.find(params[:id])
    if params[:action] == "back"
      result = BackSearchStepService.new.call(search:)
      updated_search = result.data[:search]
      redirect_to search_step_path(updated_search.current_step)
    elsif search.current_step.final?
      result = CompleteSearchService.new.call(search:)
      updated_search = result.data[:search]
      redirect_to search_step_path(updated_search.current_step)
    else
      result = AdvanceSearchStepService.new.call(search:)
      if result.success?
        updated_search = result.data[:search]
        redirect_to search_step_path(updated_search.current_step)
      else
        redirect_to search_step_path(params[:step_id]), alert: I18n.t(result.errors.first)
      end
    end
  end
end

Good 🔗 

class SearchesController < ApplicationController
  def update
    result = UpdateSearchService.new.call(request:)
    if result.success?
      redirect_to search_step_path(result.search.current_step)
    else
      redirect_to search_step_path(params[:step_id]), alert: I18n.t(result.errors.first)
    end
  end
end

class UpdateSearchService
  def call(request:)
    search_params = SearchParams.from_request(request)
    return ServiceObject::Error.new(["agent_finder.searches.invalid"]) if search_params.invalid?

    search = Search.find(search_params[:id])
    if search_params.back_pressed?
      search.go_back_a_step!
    elsif search.current_step.final?
      search.run!
      search.show_results!
    else
      search.advance_step!
    end
    ServiceObject::Success.new(search: search)
  end
end