devise installation

gem install devise
rails generate devise:install
rails generate devise User

In your routes file
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    root :to => "home#index"

In your development environment file 
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   config.action_mailer.default_url_options = { :host => 'localhost:3000' }

In your user model, I have added first_name attr_accessible 
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   class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :first_name, :email, :password, :password_confirmation, :remember_me
end


Default route setup
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devise_for :users do
    get "sign_in", :to => "devise/sessions#new"
end

now point to your browser
http://localhost:3000/sign_in



In migration file add column
====================================================================================================
  class DeviseCreateUsers < ActiveRecord::Migration
  def self.up
    create_table(:users) do |t|
      t.database_authenticatable :null => false
      t.recoverable
      t.rememberable
      t.trackable
      t.column :first_name, :string
      # t.encryptable
      # t.confirmable
      # t.lockable :lock_strategy => :failed_attempts, :unlock_strategy => :both
      # t.token_authenticatable


      t.timestamps
    end

    add_index :users, :email,                :unique => true
    add_index :users, :reset_password_token, :unique => true
    # add_index :users, :confirmation_token,   :unique => true
    # add_index :users, :unlock_token,         :unique => true
    # add_index :users, :authentication_token, :unique => true
  end

  def self.down
    drop_table :users
  end
end

**rails generate devise:views users
  It will copy view file to your view folder.

inside “config/initializers/devise.rb”
**  config.scoped_views = true” 


**device controller specific core written like
http://stackoverflow.com/questions/3546289/override-devise-registrations-controller

after write your code in controller, you have to modify your application.rb file
    config/application.rb

    paths.app.views << "app/views/devise"



Default route setup
==================================================================================================
devise_for :users do
    get "sign_in", :to => "devise/sessions#new"
end

now point to your browser
http://localhost:3000/sign_in


=====================================================================================================

 :path => allows you to setup path name that will be used, as rails routes does.
   the following route configuration would setup your route as /accounts instead of /users:
   
devise_for :users, :path => "account"






*** routes
 rake routes

**
http://localhost:3000/users/sign_in
http://localhost:3000/users/password/new
http://localhost:3000/users/sign_in
 

# how to recover undefined method `database_authenticatable' for #<ActiveRecord::ConnectionAdapters::TableDefinition:0x9faa9fc>
A. update your devise gem.
   gem devise, '2.1.1' 
   bundle install
   rails generate devise install
   rake db:migrate
   ra