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

Answer 2

Used a bit simpler approach and it worked for me on Rails 6.

class AddDimensionsToReportRecords < ActiveRecord::Migration[6.0]
  def change
    add_column :report_records, :sample_length, :decimal
    add_column :report_records, :sample_height, :decimal
    add_column :report_records, :sample_width, :decimal
  end

  def connection
    ReportRecord.connection
  end
end

And the model...

class ReportRecord < ApplicationRecord
  connects_to database: { writing: :reports_db, reading: :reports_db_replica }
end

Answer 3

Since I spent a lot of time trying with all alternatives in this and other posts, without success, here the solution that works to me

database.yml

external_database:
  adapter: postgresql
  database: <%= ENV['DATABASE_NAME'] %>
  username: <%= ENV['DATABASE_USERNAME'] %>
  password: <%= ENV['DATABASE_PASSWORD'] %>
  host: <%= ENV['DATABASE_HOST'] %>
  port: <%= ENV['DATABASE_PORT'] || 5432 %>

models/yourmodel.rb

class YourModel < ActiveRecord::Base
  establish_connection :external_database
end

your migration

class YourMigration < ActiveRecord::Migration
  def self.up
    YourModel.connection.enable_extension "plpgsql"
    YourModel.connection.create_table :your_table_name, id: :uuid do |t|
      t.text :title
      ...
    end
  end

  def self.down
    YourModel.connection.drop_table :your_table_name
  end
end

Explanation: Since the ActiveRecord::Base.establish_connection closes the connection, I'm using the connection from the model directly. Also, since I'm using UUID with the method uuid_generate_v4() as default, I enabled the extension using the same connection

Answer 4

Create a method in your migration class

def self.connection ActiveRecord::Base.establish_connection("#{Rails.env}_yourcustomenv").connection end

took me some time to realize a method declared with self was needed. This worked on Rails 4.0

Answer 5

In your config/database.yml :

development_custom_db:
  database: almoxarifado
  username: user
  password: pass
  host: localhost

Create a file contain this , in the path config/initializers/ :

module Custom
  class Base < ActiveRecord::Base
    self.abstract_class = true

    connection_name = "#{Rails.env}_custom_db"
    if Rails.application.config.database_configuration.has_key?(connection_name)
      establish_connection connection_name.to_sym
    end
  end

  class Migration < ActiveRecord::Migration
    def connection
      @_connection ||= Custom::Base.connection
    end
  end
end

Then inherit it at your migration file:

class AddDeviseToUsers < Custom::Migration
 def up
   change_table(:users) do |t|

   end
 end
end

Answer 6

You were almost at the solution. Just had to do User.connection instead of ActiveRecord::Base.establish_connection.

Take a look at the solution here: https://stackoverflow.com/a/34292909/2499227

The ActiveRecord::Base.establish_connection way always gave me issues with schema_migrations and/or connection closing, but the Model connection runs smoothly.