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Railsで変更不可な導出カラムを設定する

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例えば、こんなモデル

Circle:円形
 - radius: 半径
 - square: 面積 # このカラムは半径から導出したいので、直接変更できないようにしたい
class Circle < ActiveRecord::Base
  def radius=(radius)
    super
    self[:square] = radius*radius*Math::PI
  end

  def square=(square)
  end
end

ポイント

  • squareのセッターメソッドを無効化
  • radiusのセッターメソッドでsquareを計算
  • squareにアクセスするにはself[:square]を用いる
unosk
東京でスタートアップのエンジニアやってます。
http://neuro-inc.jp
neuro
二次交通に特化したモビリティプラットフォームRYDEの企画運営する東京のスタートアップです。
https://ryde-inc.jp/
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