乱数などを格納する列にUnique制約をかけた場合に、万が一衝突が発生したらリトライするモジュール

retry_if_collide.rb

# depends on save, save!, create, create!
module RetryIfCollide
  extend ActiveSupport::Concern

  def save(*)
    self.class._retry_if_collide { super }
  end

  def save!(*)
    self.class._retry_if_collide { super }
  end

  module ClassMethods
    def create(*)
      _retry_if_collide { super }
    end

    def create!(*)
      _retry_if_collide { super }
    end

    def _retry_if_collide
      begin
        tries ||= 3
        yield
      rescue ActiveRecord::RecordNotUnique => e
        retry if (tries -= 1) > 0
        fail "give up"
      end
    end
  end
end

CreatingWithCode

# depends on self.code
module CreatingWithCode
  extend ActiveSupport::Concern

  included do
    before_create -> { self.code = RandomString.generate unless self.code }
  end
end