stack-22265345.rb

class CreatePrices < ActiveRecord::Migration
  def change
    create_table :prices do |t|
      t.integer :price
      t.integer :old_price
      t.string  :name
    end
  end
end
-----------------------------------------------

class Price < ActiveRecord::Base

  validates_presence_of :price
  validates_presence_of :old_price

  validate :price_check

  def price_check
    if self.price > 10
      self.errors.add(:price, 'price is baaad')
    end
  end

end

---------------------------------------------------
$ rails c


> p = Price.new
=> #<Price id: nil, price: nil, old_price: nil, name: nil> 

> p.price = 12
=> 12 

p.save!
   (0.2ms)  begin transaction
[deprecated] I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message.
   (0.1ms)  rollback transaction
ActiveRecord::RecordInvalid: Validation failed: Old price can't be blank, Price price is baaad

RESULT
--------
Old Price validator executed. price_check validator executed.