Rails 4 How Overwrite Devise Respond Path Upon Error - ruby-on-rails

Question

I've been struggling for a while with this one. I have a Rails4/Devise 3.1 app with two users in the system:
Graduates
Employers
and one devise User who can be either a Graduate or Employer via a polymorphic :profile association. I have Graduates sign up via /graduate/sign_up path and employers via /employer/sign_up path both of which route to the same /views/devise/registrations/new.html.erb view (since their signup form is pretty much the same - email and password). Everything works fine, except when there is a validation error, RegistrationsController#create.respond_with resource always redirects both user types to /users path and I need to redirect them back to where they originally came from, e.g. /graduate/sign_up or /employer/sign_up respectively. I've tried replacing respond_with with redirect_to, but I end up loosing the resource object with associated error messages. Any idea guys on how this can be done?
These are my models:
class User < ActiveRecord::Base
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
belongs_to :profile, polymorphic: true
end
class Graduate < ActiveRecord::Base
has_one :user, as: :profile
end
class Employer < ActiveRecord::Base
has_one :user, as: :profile
end
Registrations controller:
class RegistrationsController < Devise::RegistrationsController
def create
build_resource sign_up_params
user_type = params[:user][:user_type]
# This gets set to either 'Graduate' or 'Employer'
child_class_name = user_type.downcase.camelize
resource.profile = child_class_name.constantize.new
if resource.save
if resource.active_for_authentication?
set_flash_message :notice, :signed_up if is_navigational_format?
sign_up(resource_name, resource)
respond_with resource, :location => after_sign_up_path_for(resource)
else
set_flash_message :notice, :"signed_up_but_#{resource.inactive_message}" if is_navigational_format?
expire_session_data_after_sign_in!
respond_with resource, :location => after_inactive_sign_up_path_for(resource)
end
else
clean_up_passwords(resource)
respond_with resource
end
end
end
Registration view (same for both, graduates and employers):
<h2>Sign up</h2>
<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
<%= devise_error_messages! %>
<div><%= f.label :email %><br />
<%= f.email_field :email, :autofocus => true %></div>
<div><%= f.label :password %><br />
<%= f.password_field :password %></div>
<div><%= f.label :password_confirmation %><br />
<%= f.password_field :password_confirmation %></div>
<%= hidden_field resource_name, :user_type, value: params[:user][:user_type] %>
<div><%= f.submit "Sign up" %></div>
<% end %>
<%= render "devise/shared/links" %>
These are my routes:
devise_for :users, :controllers => { :registrations => 'registrations' }
devise_scope :user do
match 'graduate/sign_up', to: 'registrations#new', user: { user_type: 'graduate' }, via: [:get]
match 'employer/sign_up', to: 'registrations#new', user: { user_type: 'employer' }, via: [:get]
end
root to: 'home#index'
Output of rake routes;
$ rake routes
Prefix Verb URI Pattern Controller#Action
new_user_session GET /users/sign_in(.:format) devise/sessions#new
user_session POST /users/sign_in(.:format) devise/sessions#create
destroy_user_session DELETE /users/sign_out(.:format) devise/sessions#destroy
user_password POST /users/password(.:format) devise/passwords#create
new_user_password GET /users/password/new(.:format) devise/passwords#new
edit_user_password GET /users/password/edit(.:format) devise/passwords#edit
PATCH /users/password(.:format) devise/passwords#update
PUT /users/password(.:format) devise/passwords#update
cancel_user_registration GET /users/cancel(.:format) registrations#cancel
user_registration POST /users(.:format) registrations#create
new_user_registration GET /users/sign_up(.:format) registrations#new
edit_user_registration GET /users/edit(.:format) registrations#edit
PATCH /users(.:format) registrations#update
PUT /users(.:format) registrations#update
DELETE /users(.:format) registrations#destroy
graduate_sign_up GET /graduate/sign_up(.:format) registrations#new {:user=>{:user_type=>"graduate"}}
employer_sign_up GET /employer/sign_up(.:format) registrations#new {:user=>{:user_type=>"employer"}}
root GET /

Answer 1

Apparently, the :location parameter is ignored if you have an existing template called, well, in this case, #index. I still don't understand why Devise redirects to #index or #show when the resource has errors on it.
I'll update this answer as I find out more.

Answer 2

Calling respond_with will render the default action of that resource. This I believe is the index action (/users/) and thus the cause for the redirect.
I think what you want to do is render the new action instead. Try the following:
if resource.save
...
else
clean_up_passwords(resource)
render :action => 'new'
end

Answer 3

In case of respond_with, for an html response - if the request method is get, an exception is raised but for other requests such as post the response depends on whether the resource has any validation errors (i.e. assuming that an attempt has been made to save the resource, e.g. by a create action) -
If there are no errors, i.e. the resource was saved successfully, the
response redirect's to the resource i.e. its show action.
If there are validation errors, the response renders a default action,
which is :new for a post request or :edit for patch or put.
source: http://apidock.com/rails/v4.1.8/ActionController/MimeResponds/respond_with
For your case, something like render 'view_path' in place of respond_with block should work.