Monkey patching Devise (or any Rails gem) - ruby-on-rails

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 want to change them to :success and :error so that I can display nice green/red boxes with Bootstrap.)
So I want to be able to somehow override the set_flash_message method in DeviseController.
Here's the new method:
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
But I just don't know where to put it.
UPDATE:
Based on an answer I created a config/initializers/overrides.rb file with the following code:
class DeviseController
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
But this causes an error on every Devise action:
Routing Error: undefined method 'prepend_before_filter' for
Devise::SessionsController:Class

Answer 1

If you try to reopen a class, it's the same syntax as declaring a new class:
class DeviseController
end
If this code is executed before the real class declaration, it inherits from Object instead of extending the class declared by Devise. Instead I try to use the following
DeviseController.class_eval do
# Your new methods here
end
This way, you'll get an error if DeviseController has not been declared. As a result, you'll probably end up with
require 'devise/app/controllers/devise_controller'
DeviseController.class_eval do
# Your new methods here
end

Answer 2

Using Rails 4 #aceofspades answer didn't work for me.
I kept getting require': cannot load such file -- devise/app/controllers/devise_controller (LoadError)
Instead of screwing around with load order of initializers I used the to_prepare event hook without a require statement. It ensures that the monkey patching happens before the first request. This effect is similar to after_initialize hook, but ensures that monkey patching is reapplied in development mode after a reload (in prod mode the result is identical).
Rails.application.config.to_prepare do
DeviseController.class_eval do
# Your new methods here
end
end
N.B. the rails documentation on to_prepare is still incorrect: See this Github issue

Answer 3

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.

Answer 4

What about adding in the override initializer and alias for the attributes of the flash hash, like this:
class ActionDispatch::Flash::FlashHash
alias_attribute :success, :notice
alias_attribute :error, :alert
end
This should allow your application to read flash[:notice] or flash[:success](flash.notice and flash.success)

Answer 5

You need to overwrite DeviseController while keeping around its superclass, in your initializer.
Something like:
class DeviseController < Devise.parent_controller.constantize
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

Answer 6

I know this is an old thread but this might still be helpful. You should be able to require the file from the gem directory using the engine called_from path.
require File.expand_path('../../app/helpers/devise_helper',Devise::Engine.called_from)
require File.expand_path('../../app/controllers/devise_controller',Devise::Engine.called_from)
DeviseController.class_eval do
# Your new methods here
end

Answer 7

This is the kind of thing that you will want to put on initialize rails folder, because it's a custom config for this application in particular, second you should use like so:
class DeviseController
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
then you should get the expected behavior.
hope it helps since i dont tested, of not pls give a feedback and i will help you try something diferent.