Another service layer example, arguing for dynamically instantiated services rather than static class methods.

README.md

OO Service Layer Example

The revised (OO) AnalyticsService has an SRP violation. It knows:

• How to capture analytics
• When it should and shouldn't turn itself off

A more OO approach would to remove the second responsibilty and have something like the above where you have an that is object repsonsible for configuration.

I like to make use of the 'null object' pattern in these scenarios where I have a an innocuous object, in this case a service, that that doesn't do anything.

If that seems heavy weight, it is more ceremony than the typical Rails way but having the interface on services be #call we can substitute the NullAnalyticsService for a lambda, elimating the need for another object.

app.rb

AnalyticsService = Class.new do
  def initialize(dependencies)
    # you will probably need to configure something.
  end

  def call(user, event)
    # record analytics
  end
end

NullAnalyticsService = Class.new do
  def call(user, event)
    # doesn't do anything
  end
end

Application = Class.new do
  def initialize(env)
    @env = env
  end

  def buy_shoes(request)
    BuyShoesService.new(
      :analytics_service => analytics_service,
    ).call(request)
  end

  private

    attr_reader :env

    def analytics_service
      analytics_enabled? ?
        AnalyticsService.new(some_dependencies) :
        NullAnalyticsService.new
    end

    def analytics_enabled?
      !!env.fetch("ANALYTICS_ENABLED", false)
    end
end

ShoesController = Class.new(ApplicatonController) do
  def buy
    app.buy_shoes(self)
  end

  private

    def app
      Application.new(ENV)
    end
end