present?メソッドとpresenceメソッドの違い

present?メソッドとは

対象のオブジェクトがnil, "", " "(半角スペース), , {}(空のハッシュ)の時にfalase,それ以外の場合はtrueを返すメソッド(!blank?と同じ）。

engineer = 'aoki'
engineer.present?
=> true

engineer = nil
engineer.present?
=> false

engineer = ""
engineer.present?
=> false

presenceメソッドとは

present?の結果がtrueの時、レシーバ自身を返し、`present? の結果が false のときは nil を返すメソッド。

engineer = 'aoki'
engineer.presence
=> 'aoki'

engineer = nil
engineer.presence
=> nil

engineer = ""
engineer.presence
=> nil

参考

[ActiveSupport の便利メソッド: try, blank?, present?, presence]
(http://www.techscore.com/blog/2012/12/25/activesupport-%E3%81%AE%E4%BE%BF%E5%88%A9%E3%83%A1%E3%82%BD%E3%83%83%E3%83%89-try-blank-present-presence/)