interview

transaction.rb

class Finance < ActiveRecord::Base
  validate :check_amount

  def check_amount
    errors.add(:check_amount, 'quantity limit over!') if amount > 100
  end
end

first = Finance.first
second = Finance.last
# puts second.amount
# => 90

ActiveRecord::Base.transaction do
  first.update(amount: 500)
  second.update(amount: 80)
end