Code moved out of the adapter

cronjob.rake

namespace :cron
  task :validate_models => [:environment] do
    UseCases::ValidatesPostsAndComments.new.run
  end
end

validates_posts_and_comments.rb

module UseCases
  class ValidatesPostsAndComments
    def run
      [Post, Comment].each do |klass|
        klass.all.each do |obj|
          ErrorMailer.report_errors('me@example.com', obj) unless obj.valid?
        end
      end
    end
  end
end

That's wicked!