Rails migrate with different databases

Question

I need use Devise with a existing user table in another database, so I config my database.yml:

development:
  adapter: postgresql
  encoding: unicode
  database: almoxarifado
  pool: 5
  timeout: 5000
  username: user
  password: pass
  host: localhost

users_development:
  adapter: postgresql
  encoding: unicode
  database: portal 
  pool: 5
  timeout: 5000
  username: user
  password: pass
  host: localhost
  schema_search_path: users  

In my model I wrote this code:

class User < ActiveRecord::Base
  establish_connection "users_#{Rails.env}"
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable
end

When I run Rails c and call model class this work very well.

A migration file:

class AddDeviseToUsers < ActiveRecord::Migration
  def self.up
    ActiveRecord::Base.establish_connection "users_#{Rails.env}"
    change_table(:users) do |t|
      ## Database authenticatable
      t.string :email,              :null => false, :default => ""
      t.string :encrypted_password, :null => false, :default => ""

      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at

      ## Rememberable
      t.datetime :remember_created_at

      ## Trackable
      t.integer  :sign_in_count, :default => 0, :null => false
      t.datetime :current_sign_in_at
      t.datetime :last_sign_in_at
      t.string   :current_sign_in_ip
      t.string   :last_sign_in_ip

      ## Confirmable
      # t.string   :confirmation_token
      # t.datetime :confirmed_at
      # t.datetime :confirmation_sent_at
      # t.string   :unconfirmed_email # Only if using reconfirmable

      ## Lockable
      # t.integer  :failed_attempts, :default => 0, :null => false # Only if lock strategy is :failed_attempts
      # t.string   :unlock_token # Only if unlock strategy is :email or :both
      # t.datetime :locked_at


      # Uncomment below if timestamps were not included in your original model.
      # 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
    ActiveRecord::Base.establish_connection "#{Rails.env}"
  end

  def self.down
    # By default, we don't want to make any assumption about how to roll back a migration when your
    # model already existed. Please edit below which fields you would like to remove in this migration.
    raise ActiveRecord::IrreversibleMigration
  end
end

But rake db:migrate return this error:

==  AddDeviseToUsers: migrating =======================================
-- change_table(:users)
rake aborted!
An error has occurred, this and all later migrations canceled:

undefined method `rollback' for #<ActiveRecord::ConnectionAdapters::ClosedTransaction:0xbb06767c>
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

Answer 1

=================================UPDATE=================================

I find a nice article talking about it: http://www.thegreatcodeadventure.com/managing-multiple-databases-in-a-single-rails-application/

=================================UPDATE=================================

I just put establish_connection out of a migrate class.

ActiveRecord::Base.establish_connection "users_#{Rails.env}"
class AddDeviseToUsers < ActiveRecord::Migration
  def self.up

    change_table(:users) do |t|
      ## Database authenticatable
      t.string :email,              :null => false, :default => ""
      t.string :encrypted_password, :null => false, :default => ""

      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at

      ## Rememberable
      t.datetime :remember_created_at

      ## Trackable
      t.integer  :sign_in_count, :default => 0, :null => false
      t.datetime :current_sign_in_at
      t.datetime :last_sign_in_at
      t.string   :current_sign_in_ip
      t.string   :last_sign_in_ip

      ## Confirmable
      # t.string   :confirmation_token
      # t.datetime :confirmed_at
      # t.datetime :confirmation_sent_at
      # t.string   :unconfirmed_email # Only if using reconfirmable

      ## Lockable
      # t.integer  :failed_attempts, :default => 0, :null => false # Only if lock strategy is :failed_attempts
      # t.string   :unlock_token # Only if unlock strategy is :email or :both
      # t.datetime :locked_at


      # Uncomment below if timestamps were not included in your original model.
      # 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
  end

  def self.down
    # By default, we don't want to make any assumption about how to roll back a migration when your
    # model already existed. Please edit below which fields you would like to remove in this migration.
    raise ActiveRecord::IrreversibleMigration
  end
end