例外処理

class LoginFailed < StandardError
end

class ApplicationController < Actioncontroller::Base
  rescue_from LoginFailed, with: :login_failed

  def login_failed
    render template: "shared/login_failed", status: 401
  end
end

class LoginController < ApplicationController
  def create
    @user = User.where(name: params[:name], password: params[:password]).find
    raise LoginFailed unless @user
    略
  end
end

begin
  （例外が起きるかもしれない処理）
  ...
rescue => e
  logger.error.e.message
  logger.error e.backtrace
end