【Rails】deviseのvalidatableを理解する

validatableモジュールのソースコード

devise/models/validatable.rb

# frozen_string_literal: true

module Devise
  module Models
    # Validatable creates all needed validations for a user email and password.
    # It's optional, given you may want to create the validations by yourself.
    # Automatically validate if the email is present, unique and its format is
    # valid. Also tests presence of password, confirmation and length.
    #
    # == Options
    #
    # Validatable adds the following options to devise_for:
    #
    #   * +email_regexp+: the regular expression used to validate e-mails;
    #   * +password_length+: a range expressing password length. Defaults to 6..128.
    #
    module Validatable
      # All validations used by this module.
      VALIDATIONS = [:validates_presence_of, :validates_uniqueness_of, :validates_format_of,
                     :validates_confirmation_of, :validates_length_of].freeze

      def self.required_fields(klass)
        []
      end

      def self.included(base)
        base.extend ClassMethods
        assert_validations_api!(base)

        base.class_eval do
          validates_presence_of   :email, if: :email_required?
          if Devise.activerecord51?
            validates_uniqueness_of :email, allow_blank: true, case_sensitive: true, if: :will_save_change_to_email?
            validates_format_of     :email, with: email_regexp, allow_blank: true, if: :will_save_change_to_email?
          else
            validates_uniqueness_of :email, allow_blank: true, if: :email_changed?
            validates_format_of     :email, with: email_regexp, allow_blank: true, if: :email_changed?
          end

          validates_presence_of     :password, if: :password_required?
          validates_confirmation_of :password, if: :password_required?
          validates_length_of       :password, within: password_length, allow_blank: true
        end
      end

      def self.assert_validations_api!(base) #:nodoc:
        unavailable_validations = VALIDATIONS.select { |v| !base.respond_to?(v) }

        unless unavailable_validations.empty?
          raise "Could not use :validatable module since #{base} does not respond " <<
                "to the following methods: #{unavailable_validations.to_sentence}."
        end
      end

    protected

      # Checks whether a password is needed or not. For validations only.
      # Passwords are always required if it's a new record, or if the password
      # or confirmation are being set somewhere.
      def password_required?
        !persisted? || !password.nil? || !password_confirmation.nil?
      end

      def email_required?
        true
      end

      module ClassMethods
        Devise::Models.config(self, :email_regexp, :password_length)
      end
    end
  end
end

インクルードされるバリデーション

フィールド	バリデーション
メールアドレス	validates_presence_of
	validates_uniqueness_of
	validates_format_of
パスワード	validates_presence_of
	validates_confirmation_of
	validates_length_of

パラメータを追加した場合

パラメータを追加したならば、いつものように手で書くのがよさそうです。

app/models/user.rb

# frozen_string_literal: true

class User < ApplicationRecord
  devise :database_authenticatable,
         :validatable,
         :registerable,
         :recoverable,
         :rememberable,
         :confirmable

  validates :screen_name,
            presence: true,
            length: { maximum: 20 },
            uniqueness: { case_sensitive: false }
end

参考

github.com