Monkey patching Devise (or any Rails gem)

Question

I\'m using the Devise authentication gem in my Rails project, and I want to change the keys it\'s using in flash alerts. (Devise uses :notice and :alert flash keys, but I wa

Answer 1

In your initializer file :

module DeviseControllerFlashMessage
  # This method is called when this mixin is included
  def self.included klass
    # klass here is our DeviseController

    klass.class_eval do
      remove_method :set_flash_message
    end
  end

  protected 
  def set_flash_message(key, kind, options = {})
    if key == 'alert'
      key = 'error'
    elsif key == 'notice'
      key = 'success'
    end
    message = find_message(kind, options)
    flash[key] = message if message.present?
  end
end

DeviseController.send(:include, DeviseControllerFlashMessage)

This is pretty brutal but will do what you want. The mixin will delete the previous set_flash_message method forcing the subclasses to fall back to the mixin method.

Edit: self.included is called when the mixin is included in a class. The klass parameter is the Class to which the mixin has been included. In this case, klass is DeviseController, and we call remove_method on it.