grit| commit

daily learnings as a ruby dev

Build Robust & Production Quality Applications - Lesson 8: Beyond MVC - Service Objects

13 Jul 2015

Service Objects

Just like we can extract domain logic into domain objects, we can extract business level logic into service objects. Currently, the below process is modeling the Credit Deduction Business Process. Let's extract that into a Service Object called CreditDeduction.

#apps/controllers/todos_controller.rb
def create
  @todo = Todo.new(params[:todo)]
  credit = Credit.new(current_user)

  if @todo.save_with_tags
    if UserLevelPoicy.new(ccurent_user).premium?
    credit = credit - 1
  else
    credit = credit - 2
  end

  credit.save

  if credit.depleted? < 0
    AppMailer.notify.insufficient_funds
  elsif credit.low_balance?
    AppMailer.notify_low_balance
  end
    redirect_to root_path
  else
    render :new
  end

Create the Service Policy called CreditDeduction

#app/services/credit_deduction.rb
Class CreditDeduction


end

Extract business process related Code

#app/services/credit_deduction.rb
Class CreditDeduction
  attr_accessor :user

  def initialize(user)
    @user = user
  end

  def deduct_credit
    if UserLevelPoicy.new(ccurent_user).premium?
      credit = credit - 1
    else
      credit = credit - 2
    end

    credit.save

    if credit.depleted? < 0
      AppMailer.notify.insufficient_funds
    elsif credit.low_balance?
      AppMailer.notify_low_balance
    end
  end
end

Update the TodoController

#apps/controllers/todos_controller
def create
  @todo = Todo.new(params[:todo)]
  credit = Credit.new(current_user)

  if @todo.save_with_tags
    CreditDeduction.new(credit, current_user).deduct_credit

    redirect_to root_path
  else
    render :new
    end
  end
end

Move instatiating a new Credit Object to your Service Policy

#app/services/credit_deduction.rb
Class CreditDeduction
  attr_accessor :credit, :user

  def initialize(credit, user)
    @credit = Credit.new(user)
    @user = user
  end

  def deduct_credit
    if UserLevelPoicy.new(ccurent_user).premium?
      credit = credit - 1
    else
      credit = credit - 2
    end

    credit.save

    if credit.depleted? < 0
      AppMailer.notify.insufficient_funds
    elsif credit.low_balance?
      AppMailer.notify_low_balance
    end
  end
end
#apps/controllers/todos_controller
def create
  @todo = Todo.new(params[:todo)]

  if @todo.save_with_tags
    CreditDeduction.new(current_user).deduct_credit

    redirect_to root_path
  else
    render :new
    end
  end
end

Related Posts