Setting Devise Login to be root page

I am using the following code for my routes:

devise_for :user, 
  :as => '', 
  :path_names => { 
    :sign_in => "", 
    :sign_out => "logout", 
    :sign_up => "register" 
  }

But when I'm logged out and I goto /logout I get the following error:

> No route matches {:action=>"new", > :controller=>"devise/sessions"}

How do I setup the root path to be to :sign_in action?

To follow on from the people who are asking about the error Could not find devise mapping for path "/" there is a workaround.

You'll find that there is a clue in your logs which will probably say:

[Devise] Could not find devise mapping for path "/".
This may happen for two reasons:

1) You forgot to wrap your route inside the scope block. For example:

  devise_scope :user do
    match "/some/route" => "some_devise_controller"
  end

2) You are testing a Devise controller bypassing the router.
   If so, you can explicitly tell Devise which mapping to use:
   
   @request.env["devise.mapping"] = Devise.mappings[:user]

So I retried the approach but instead wrapping it (as @miccet suggets) inside a scope block:

devise_scope :user do
  root to: "devise/sessions#new"
end

This worked fine for me

devise_for :users

devise_scope :user do
  authenticated :user do
    root 'home#index', as: :authenticated_root
  end

  unauthenticated do
    root 'devise/sessions#new', as: :unauthenticated_root
  end
end

Just like this, tested on Rails Rails 4.1.0.rc1.

root :to => "devise/sessions#new"

I needed to set the default home root. I felt like I had tried this all night last night (prior to posting the question), but it's working now. If you're logged out, Devise attempts to redirect you to the root path which I had undefined.

_{(This was posted as a suggested edit, but should have been an answer of its own. I don't know if it makes sense or not. Dear anonymous editor: feel free to repost this answer as your own, and leave me a comment so I'll delete this copy.)}

root :to => redirect("/users/login")

I got this to work with @VvDPzZ answer. But I had to modify it slightly

  devise_scope :business_owner do
    authenticated  do
      root to: 'pages#dashboard'
    end

    unauthenticated do
      root to: 'devise/sessions#new', as: 'unauthenticated_root'
    end
  end  

I had to ad to: in the root path declaration. I also removed the as: :authenticated_root because I already had some places in my application referencing root_path in links. By leaving out the as: :authenticated_root part I didn't have to change any of my existing links.

I guess you have different user roles. If you do you have to add a scope like this to the users resource:

  devise_scope :user do
    get "/logout" => "devise/sessions#destroy"
  end

You can read more about overriding devise routes here: https://github.com/plataformatec/devise/wiki/How-To:-Change-the-default-sign_in-and-sign_out-routes

Some of these solutions are way too complex. Just use Rails:

Add 'get' 'users/root', to: 'users#root' to config/routes.rb.

In UsersController do something like:

def root
  if user_signed_in?
    redirect_to root_for_signed_in_user_path (or whatever)
  else
    redirect_to new_user_session_path
  end
end

Using rails 3.2 and devise 3.2.3 I manage to setup my home page "home#index" (controller#action) as the login page making the following changes.

#1 Added the login form to the home page:

<%= simple_form_for(resource, as: resource_name, url: session_path(resource_name)) do |f| %>
    <%= f.input :email %>
    <%= f.input :password %>
    <%= f.button :submit %>
<% end %>

#2 Added methods resource_name, resource and devise_mapping to app/heldpers/application_helper.rb:

def resource_name
  :user
end

def resource
  @resource ||= User.new
end

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

#3 Created a custom sessions controller app/controllers/users/sessions_controller.rb:

class Users::SessionsController < Devise::SessionsController
    
   protected

   # This method tell sessions#create method to redirect to home#index when login fails.
   def auth_options
      { scope: resource_name, recall: 'home#index' }
   end
    
end

#4 Skip the session routes and setup the custom sessions controller in config/routes.rb:

devise_for :users, path: 'auth', skip: [:sessions],
           controllers: {
               sessions: 'users/sessions'
           }

as :user do
  get 'auth/sign_in' => 'home#index', as: :new_user_session
  post 'auth/sign_in' => 'users/sessions#create', as: :user_session
  delete 'auth/sign_out' => 'users/sessions#destroy', as: :destroy_user_session
end

I'm new on rails and I didn't know your 'device_scope' name have to be different to your 'device_for' name. Notice my example.

I tried this a hundred times a this is why it didn't work jajaja

  devise_for :user_devises, path: 'user_devises'

  devise_scope :user_devise do
    authenticated :user_devise do
      root 'home#index', as: :authenticated_root
    end
  
    unauthenticated do
      root 'devise/sessions#new', as: :unauthenticated_root
    end
  end