Ruby on rails Rails通过集合创建模型\u id如何防止重新关联？

假设我有两个模型

class Car < ActiveRecord::Base
  has_many :wheels
end

class Wheel < ActiveRecord::Base
  belongs_to :car
end

class-Car

将使用车轮ID为[1,2,3]的汽车创建汽车

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如何检查某个车轮是否已与另一辆车关联？

检查单个车轮

wheel = Wheel.last
wheel.car.present? # => if false then it has no association to car

检查无关联的所有车轮

wheels = Wheel.join(:car).where(:car => { :id => nil}) # => not tested yet but should work

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这个怎么样？但不知何故，我对这一点没有信心

class Car < ActiveRecord::Base

validate  :check_reassociation_wheels, on: [:create,:update]

  def check_reassociation_wheels
    wheel_ids.each do |id|
      wheel = Wheel.find(id)
      errors.add(:base, "Cannot reasociate wheel") unless (wheel.car_id.nil? || wheel.car_id == self.id)
    end  
  end
end

class-Car