ActiveRecord でバリデーションをコンテキスト毎に分けるやつ

user.rb

class User < ActiveRecord::Base
  include ValidationContext

  with_context :first do |context|
    context.validates_presence_of :name
  end

  with_context :second do |context|
    context.validates_presence_of :email
  end
end

users_controller.rb

class UsersController < ApplicationController
  before_filter :require_user

  def first
    if @user.with_context(:first) { |u| u.update_attributes(params[:user]) }
      # do something
    else
      # do something
    end
  end

  def second
    if @user.with_context(:second) { |u| u.update_attributes(params[:user]) }
      # do something
    else
      # do something
    end
  end

  private

  def require_user
    @user = User.find(params[:id])
  end
end

validation_context.rb

module ValidationContext
  extend ActiveSupport::Concern

  included do
    before_validation :reflect_context_to_associations

    def self.with_context(*contexts, &block)
      options = contexts.last.is_a?(Hash) ? contexts.last.dup : {}
      options[:if] = Array.wrap(options[:if])
      options[:if] << ->(o) { o.context.nil? || o.context.in?(contexts) }
      with_options(options, &block)
    end
  end

  attr_reader :context

  def context=(context)
    @context = context
    reflect_context_to_associations
  end

  def reflect_context_to_associations
    self.class.reflect_on_all_associations.each do |reflection|
      association = self.association(reflection.name)
      Array.wrap(association.target).each do |record|
        if record.respond_to?(:context=)
          record.context = context
        end
      end
    end
  end

  def with_context(context, &block)
    current_context, self.context = self.context, context
    yield self
  ensure
    self.context = current_context
  end
end