Ruby-on-rails – Use current_user in application controller

In your form are you passing in any other attributes, via mass assignment that don't belong to your user model, or any of the nested models?

If so, I believe the ActiveRecord::UnknownAttributeError is triggered in this instance.

Otherwise, I think you can just create your own controller, by generating something like this:

# app/controllers/registrations_controller.rb
class RegistrationsController < Devise::RegistrationsController
  def new
    super
  end

  def create
    # add custom create logic here
  end

  def update
    super
  end
end 

And then tell devise to use that controller instead of the default with:

# app/config/routes.rb
devise_for :users, :controllers => {:registrations => "registrations"}

As Andres says, the form calls helpers which are specified by Devise and so aren't present when you access a Devise form from a non-Devise controller.

To get around this, you need to add the following methods to the helper class of the controller you wish to display the form under. Alternatively, you can just add them to your application helper to make them available anywhere.

  def resource_name
    :user
  end

  def resource
    @resource ||= User.new
  end

  def devise_mapping
    @devise_mapping ||= Devise.mappings[:user]
  end

Source: http://pupeno.com/blog/show-a-devise-log-in-form-in-another-page/