ruby-on-rails – 如何使用“validates：attribute”来引用父对

“Flight”对象[我使用annotate gem来显示每个属性]：

# == Schema Information
#
# Table name: flights
#
#  id                :integer         not null,primary key
#  departure         :datetime
#  arrival           :datetime
#  destination       :string(255)
#  baggage_allowance :decimal(,)
#  capacity          :integer
#  created_at        :datetime
#  updated_at        :datetime
#

class Flight < ActiveRecord::Base
  has_many :seats
end

Ant“Seat”对象：

# == Schema Information
#
# Table name: seats
#
#  id         :integer         not null,primary key
#  flight_id  :integer
#  name       :string(255)
#  baggage    :decimal(,)
#  created_at :datetime
#  updated_at :datetime
#

class Seat < ActiveRecord::Base
  belongs_to :flight
end

您可能猜测seat.baggage值应始终小于或等于seat.flight.baggage_allowance.

所以我写了这个验证器,效果很好：

class Seat < ActiveRecord::Base

  belongs_to :flight

  def validate
      if baggage > flight.baggage_allowance
      errors.add_to_base("Your have to much baggage for this flight!")
    end 
  end  
end

然后我试着用这个更漂亮的那个重构它：

validates :baggage,:numericality => { :less_than_or_equal_to => flight.baggage_allowance },:presence => true

但它导致SeatsController中的NameError：

undefined local variable or method `flight' for #<Class:0x68ac3d8>"

比我还试过“self.flight.baggage_allowance”：

validates :baggage,:numericality => { :less_than_or_equal_to => self.flight.baggage_allowance },:presence => true

但它会引发NoMethodError异常：

undefined method `flight' for #<Class:0x67e9b40>

有没有办法让更漂亮的验证器工作？

进行此类验证的最佳做法是哪种？

谢谢.

– -编辑 – –

正如毛里西奥·林哈里斯(MaurícioLinhares)此后提出的那样,问题是可以解决的：定义：bagging_allowance符号.
我想更好地了解真正需要自定义验证的地方.
这个怎么样,是否有可能将此转换为“验证”方法？为什么？

class Seat < ActiveRecord::Base
.
.
.
def validate
  if flight.capacity <= flight.seats.size
    errors.add_to_base("The flight is fully booked,no more seats available!")
  end
end

再次感谢你.