Example of a simple use of eval()

gistfile1.rb

# Goes with http://joemerante.blogspot.com/2014/07/may-tmil-touch-of-eval.html

# app/models/subscription.rb
class Subscription < ActiveRecord::Base
  belongs_to :plan
  after_create :set_expiration
  # ... 

  def expired?
    self.expiration < DateTime.now
  end

  # ....

  private

  def set_expiration
    # plan.duration is stored as "2.weeks", "3.months" etc
    self.expiration = DateTime.now + eval(plan.duration)
    save!
  end
end


# spec/models/subscription_spec.rb
require 'spec_helper'

describe Subscription do
  
  it "sets an expiration in a callback" do 
    Timecop.freeze(DateTime.now) do
      user = FactoryGirl.create(:user)
      plan = FactoryGirl.create(:plan) # duration on factory is "3.months"
      subscription = FactoryGirl.create(:subscription, user_id: user.id, plan_id: plan.id)
      expect(subscription.expiration).to eq(DateTime.now + 3.months)
    end
  end

end