9_devise_learning.rb

## << Devise::RegistrationController

### Build an user (resource) object from temporary
build_resource(sign_up_params.select{|k,v| v.present?})
# > #<User id: nil, created_at: nil, updated_at: nil, email: "a@b.c", encrypted_password: "$2a$10$HufMLSGEoWzbwhVO.IRztuvE8NKTrQgaXNZthem3wid...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 0, current_sign_in_at: nil, last_sign_in_at: nil, current_sign_in_ip: nil, last_sign_in_ip: nil>

### :validatable module in devise. (took me three hours)
# http://stackoverflow.com/questions/21103138/handle-activerecordrecordnotunique-in-devise-registrations-controller/29792359#29792359
# ActiveRecord::RecordNotUnique in Users::RegistrationsController#create
# PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "index_users_on_email" DETAIL: Key (email)=() already exists. : INSERT INTO "users" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "id"
## To solve this error, just add :validatable in user.rb
class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, 
  			 :registerable,
         :recoverable,
         :rememberable, 
         :trackable
end