alias_method_chain

role.rb

class Role < ActiveRecord::Base
  belongs_to :user
end

user.rb

class User < ActiveRecord::Base
  has_many :roles
  accepts_nested_attributes_for :roles

  # Работает!
  # [begin]
  def roles_attributes=(value)
    ActiveRecored::Base.logger.info "123"
    self.roles_attributes_without_saving=(value)
  end
  alias_method_chain :roles_attributes=, :saving
  # [end]

  # Не работает!
  # [begin]
  def roles_attributes=(value)
    ActiveRecored::Base.logger.info "123"
    super       # NoMethodError: super: no superclass method `roles_attributes=' for
  end
  # [end]
end