# 'app/models/book.rb'
class Book < ActiveRecord::Base

  has_many :book_pubhouses, :dependent => :destroy # уничтожать вместе с основным экземпляром
  has_many :pubhouses, :through => :book_pubhouses # through указывает Rails приложению зависимость двух моделей через третью, теперь мы можем использовать Book.pubhouses напрямую

  # валидация
  validates :title, :presence => true
  validates :title, :uniqueness => true
  validates :title, :length => { :maximum => 150 }
  validates :description, :length => { :maximum => 2000 }
  
end

# 'app/models/pubhouse.rb'
class Pubhouse < ActiveRecord::Base

  has_many :book_pubhouses, :dependent => :destroy
  has_many :shops, :through => :book_pubhouses
  
  validates :title, :presence => true
  validates :title, :uniqueness => true
  validates :title, :length => { :maximum => 150 }
  validates :address, :length => { :maximum => 2000 }

end

# 'app/models/book_pubhouse.rb'
class BookPubhouse < ActiveRecord::Base

  belongs_to :book
  belongs_to :pubhouse
  
  validates :book_id, :presence => true
  validates :pubhouse_id, :presence => true
  validates :pubhouse_id, :uniqueness => {:scope => :book_id}

end